Open access peer-reviewed chapter

Xanthobacter autotrophicus an Endophytic Beneficial Bacterium for Wheat and Other Plants: A Short Review

Written By

Juan Manuel Sánchez-Yañez

Submitted: 07 October 2021 Reviewed: 17 December 2021 Published: 23 March 2022

DOI: 10.5772/intechopen.102066

From the Edited Volume

Current Trends in Wheat Research

Edited by Mahmood-ur-Rahman Ansari

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The endophytic genus plant growth promoting bacteria (EPGPB) known as Xanthobacter autrotrophicus is one of the most interesting option to apply on the production of wheat (Triticum aestivum), and other domestic crops lettuce (Lactuca sativa), tomato (Solanum lycopersicum) rice (Oriza sativa) maize (Zea mays): under all types of agriculture systems: open field, protecting one or either organic sustainable type. The aims of this review is to analyze the qualities of X. autotrophicus as useful EPGPB for sustainable production of wheat and other crops regarding its capacity as able to fix molecular nitrogen (N2) as well as by transforming plant metabolic compounds in phytohormons, including phosphatase enzyme for solubilizing phosphate to solve different soil problems related with its fertility also some phytopathological like to stop of growing weed as Arabidopsis thaliana which are competing with health growth of domestic plants. Beside the potencial of X. autotrophicus for bioremediation of environmental polluted by chemicals.


  • soil proprieties
  • cereals
  • vegetables and green nitrogen fertilizer
  • endophytic plant growth promoting bacteria
  • health

1. Introduction

The well know endophytic plant growth promoting bacterium Xanthobacter autotrophicus, was described as Corynebacterium autotrophicus due its specific genetic qualities to grow under chemolithoautotrophically and for being able to fix molecular nitrogen (N2) as nitrogen source [1]: X. autotrophicus are rods, according to growth condition show pleomorphism depends on the species and the carbon and nitrogen source on which they are grown. X. autotrophicus is a Gram-type negative rods with high concentrations of polyphosphate granule belongs phylogenetically to the family Hyphomicrobiaceae in the class Alphaproteobacterial, grow heterotrophically under aerobic or microaerophilic conditions with acids, alcohols, and selectively with some carbohydrates as energy and carbon source like: fructose, galactose, mannose and sucrose [2, 3, 4, 5, 6, 7].

The endophyte plant growth promoting bacteria: X. autotrophicus can fix dinitrogen under heterotrophic and thioautotrophic conditions is able to grow with H2 plus O2 or H2 + Na2S2O3 as energy source and with CO2 as only inorganic carbon source [8, 9, 10] at reduced O2 tension [11, 12] in the absence of organic or inorganic nitrogen (N) compounds as aminoamides, peptides, proteins, nucleotides, well known sources as NH4+ (ammonia) or NO3 (nitrate) at the soil [13] and culture artificial media [14]. On the basis of their numbers, X. autotrophicus should be regarded as an associative symbiosis diazotroph due although entering roots of wheat (Triticum aestivum), bean (Phaseolus vulgaris), root beet (Beta vulgaris), rice (Oriza sativa) [15] tomato (Solanum lycopersicum), lettuce (Lactuca sativa) [16, 17] does not form nodules the way do symbiotic N2-fixing bacteria in legume as Bradyrhizobium japonicum does. The special position of X. autotrophicus among the chemolithoautotrophic and other the N2-fixing aerobic bacteria [1, 11], X. autotrophicus is able to grow with H2/CO2/O2 or to have high hydrogenase activity [10, 18], beside reaction of nitrogenase as the other well-known genera: Azotobacter, Derxia, Bradyrhizobium and Rhizobium [19, 20]. Originally, one key taxonomic property for discriminating X. autotrophicus from other genera yellow pigmented zeaxanthin dirhamnoside bacteria, including diazotrophs [2]. Xanthobacter strains can be isolated easily if certain conditions are applied: no other or very limiting sources of nitrogen other than N2 or H2/CO2/O2/N2 [9, 11] as gas phase providing an electron donor, a carbon source, electron acceptors, in liquid media; yellow colonies are showed on nutrient agar plates [1, 6]. Because its metabolic diversity Xanthobacter species are widespread in natural habitats [21] as is showed in Table 1.

Biochemical characteristics1.2.3.
Cell morphology: rods
Morphology as rod on free carbon and nitrogen media+++
Slime production+++
Zeaxanthine dirhamnoside (yellow)+++
Zeaxanthine (orange, pinkish)
Motility under autotrophic growth conditionsddd
Vitamins required for growth+++
Sensitivity to chloramphenicol
Under autotrophic growth at 35°C+++
Utilization of hexoses+++
Growth on nutrient broth+++
Growth on glutamine as carbon source+++
Growth on citrate+++
Degradation of aromatic compounds+++
Degradation of cyclohexene (and derivatives)+++
Utilization of methanol+++
Utilization of hydrocarbons+++

Table 1.

Main biochemical characteristics among some species of the genus Xanthobacter.a

1 = X. autotrophicus in the reference; 2 = X. autotrophicus; 3 = X. autotrophicus repetitions.

Lime production in glucose.

Pale yellow indicating low concentration [6, 22, 23, 24, 25, 26].

Symbols and abbreviations: +, positive; (+), positive except for some unusual strains; −, negative; (−), negative except for some unusual strains; +/− not determined; TCA = tricarboxylic acid.


2. Phylogeny and taxonomy of Xanthobacter spp

The phylogenetic position of Xanthobacter based on 16S rRNA sequence analysis published in Bergey’s Manual of Systematic Bacteriology, showed that genus Xanthobacter is part of phylum Proteobacteria, class Alpha proteobacteria order Rhizobiales family Xanthobacteraceae. However, using phylogenetic trees constructed on the basis of 16S rRNA sequence comparisons, the type strains of Aquabacter spiritensis and Azorhizobium caulinodans are intermingled with the otherwise well-defined genus cluster Xanthobacter, Aquabacter and Azorhizobium (both single species genera are recognized as separate genera V and VI within the same family Hyphomicrobiaceae, some of the key properties described for the type species X. autotrophicus it is suggested to keep the separate genera names despite the 16S rRNA sequence similarity [22]. The 16S rRNA sequence is more than 98% similar to those of X. flavus and X. autotrophicus strains as is showed in Figure 1 [26, 8, 23, 27]. The morphology and some of the physiological proprieties are different to separate species, supported by the low below 50% DNA-DNA hybridization data as well as tricarboxylic acid or TCA cycle intermediate; (1) synthesis of the water insoluble zeaxanthin dirhamnoside, showed by the yellow colonies; (2) normally to grow chemolithoautotrophically; and (3) able to fix dinitrogen under microaerophilic chemolithoautotrophic or heterotrophic conditions [1, 28]. Other characteristics are given in Table 1, Xanthobacter is free-living in soil and water as well as root-associated but never noduling, exhibits acetylene reduction as an indirect technique for nitrogen fixing capacity. Other features of Xanthobacter a are the h i g h G+C related with some flavobacteria and Cytophaga spp: (1) antibiotic pattern sensitivity [17] (2) positive reaction for catalase, oxidase and phosphatase acid and alkaline types; (3) negative reaction for methyl red, gas from carbohydrates, and the Voges-Proskauer test; and (4) containing ubiquinones Q10 and Q8 like is in Beijerinckia, and Azotobacter, are important for truly identification of these species, demonstration of the pigment zeaxanthin dirhamnoside and acquisition of the 16S rDNA sequence are important [2, 6, 21].

Figure 1.

Photographs of X. autotrophicus (a) macroscopic morphology in a mineral medium without sucrose either ammonium nitrate (MMWSA) under autotrophic conditions after 30 h incubation at 35°C, (b) and (c) microscopic morphology of X. autotrophicus according at Gram negative in MMWSA under the same incubation condition (photos from Environmental Laboratory-UMSNH, Sánchez-Yañez et al., 2020).


3. Taxonomy

The most identifications of environmental isolates are done by 16S rRNA sequence analysis, in a first common identification step, diagnostic taxonomic properties are: (1) yellow, “fried egg” shaped colonies with several amounts of slime production under cultivation media specific conditions; (2) rods, some species have strong polymorphic, branched, twisted cell morphology growing on nutrient agar with larger amounts of polyphosphate granula, can lead to the false impression of a Gram-positive staining reaction; however all Xanthobacter stain are truly Gram negative when is using a counterstain in polyphosphate-free cells of X. autotrophicus [2, 22, 24].


4. Isolation cultivation and axenic culture

Selective enrichment cultures. For isolation purposes, the use of free carbon and nitrogen agar medium as a selective medium is recommended for recovering Xanthobacter from; soil, upper layers of marine or freshwater sediments, lake water, steam and root of aal types of plants. Because of slime formation by X. autotrophicus of agar plates free carbon and nitrogen source. Frequently, other oligotrophic organisms grow as contaminants in the slimy colonies of Xanthobacter easy to separate in nutrient agar the following basal medium can be used for autotrophic as well as heterotrophic growth except when urea is used as nitrogen source. No vitamins or additions of yeast extract as growth factor are required for most X. autotrophicus, enrichment 100 mg of yeast extract per liter to the mineral medium can reduce an extended lag time for autotrophic growth under free carbon and nitrogen-fixing. In order to demostrate its capacity for fixing N2 is important not to add any inorganic or organic nitrogen source. During isolation, a vitamin solution any mixture containing biotin can enrichment to stimulate is growth, absence of ammonium, or amino acids, peptide, protein as any organic nitrogen source [29, 30]. For heterotrophic growth, common carbon sources are used: 0.5% sugars, 0.3% (v/v) alcohols or 0.4–0.8% organic acids. For growth under non-N2-fixing conditions, 0.1% of ammonium chloride or sulfate is common. The exact composition of this medium is not critical, and good results have been obtained with free sucrose and nitrogen agar medium, for storge sterile soil is one the easy and best one to preserve viability for relative long period of time. X. autotrophicus, studied in more detail, most of the strains tested grow at pH 5.0–8.5 while pH recommend is about 6.8–7.2 and its temperature 30–37°C. The morphological features of Xanthobacter can be used initially for identification. Colony morphology depends on the type of carbon and nitrogen source and growth conditions. On most carbohydrates, the colonies of main species are large from 1 to 5 mm in diameter, smooth, convex, circular, filiform, opaque, and typically egg-yolk yellow color due to zeaxanthin dirhamnoside (see Figure 2a). The colonies become less yellow and less opaque as the amount of slime increases. The production of slime on nutrient agar plates frequently results in colonies resembling fried eggs [15]. Zeaxanthin dirhamnoside is water-insoluble, in contrast to the reddish/pinkish/brown pigment or to the yellow-green diffusing pigments with fluorescence of Beijerinckia and Derxia the other yellowish diazotroph isolated with well-known methods. The latter fact also makes it easy to distinguish Xanthobacter from Derxia colonies, which turn brown with age besides other morphological and biochemistry characteristics [5, 31]. Xanthobacter strains are sensitive to wide range of antibiotics, but the response depends on the method applied broth cultures or the use of Difco (Dispense-O-Disk minifilters). X. autotrophicus was sensitive to ampicillin, penicillin, chloramphenicol, erythromycin, novobiocin, and polymyxin B, but they were resistant to erythromycin and bacitracin. Few strains can grow on violet red-bile medium (Oxoid), deoxycholate medium (Oxoid), tellurate agar (Difco), and mineral medium supplemented with crystal violet red colonies [6, 32, 33].

Figure 2.

Phylogeny and taxonomy of Xanthobacter spp.

4.1 Methods of storage

Xanthobacter cultures are grown on chemolithoautotrophic agar slants stored 1.5 years at 4°C after sealing the tubes tightly with parafilm. Also, liquid cultures grown under chemolithoautotrophic conditions mineral medium with 0.02% (w/v) yeast extract have been kept for more than 15 months at 4°C and, of course if glycerol is used as suspended solution at 40–60% (v/v) final, at –20°C and –75°C for more than 8 years. For long-term storage, cultures should be lyophilized on skim milk at 10% now sterile soil is an easy and safe technique [34, 35].


5. Autotrophy and nitrogen fixation capability

X. autotrophicus can use H2 from thiosulfate as source of energy for CO2 fixation, when grown heterotrophically in the presence of gas mixture, Xanthobacter species fix CO2 mainly via the ribulose-biphosphate pathway but phosphoenolpyruvate carboxylase activity also has been reported. Have shown that the fixation of CO2 plays an important role in the degradation of aliphatic epoxides and ketones by novel carboxylases [5, 8, 10, 24]. X. autotrophicus fixes N2 under heterotrophic growth conditions with sucrose as a carbon source; however, N2 fixation was showed for several strains of X. autotrophicus with 15N2 incorporation into cell protein [12, 18]. The biochemical studies on the enzyme and its relationship to oxygen have been restricted to X. autotrophicus. The nitrogenase in these two strains is similar to that in other aerobic diazotrophs [2, 6, 36, 37]. There is strong variation among the strains in respect to the optimal O2 concentration for growth under N2-fixing conditions, for X. autotrophicus. The optimal partial pressures of O2 for acetylene reduction are 5 and 2.5 kPa to 0.36 kPa. However, the alternative vanadium nitrogenase system could not yet be shown through substantial ethane synthesis or improving its growth when vanadium is added to molybdenum deprived medium [1, 14, 38].


6. Natural habitats

The known habitats of Xanthobacter are depending on its physiological properties, underline its catabolic versatility [39]. The sources for isolated strains include oil-contaminated soil and sludge from Japan [5], marine sediments, water and sediment samples from fresh- water lakes, soil of flooded rice fields, rhizosphere of wetland street ditches and wet meadow soil and garden soil from Europe, South Africa, North America, and Asia, sewage samples [3, 13, 40] and tree leaves [2041]. Xanthobacter is ubiquitous in microaerophilic environments with decaying organic material or matter [19] containing sufficient concentrations of H2 and CO2 and other metabolic compounds products of anaerobic microbial activity, such as organic acids and alcohols. Xanthobacter species are important in the microaerophilic interface between the anaerobic and aerobic habitats. Therefore, it is very likely that Xanthobacter, and possibly also other N2-fixing Knallgas bacteria, can be found in habitats other not yet known [42, 43]. According to literature, no thermophilic, psychrophilic, or halophilic strains have been isolated [44]. Furthermore, it is not clear whether Xanthobacter contributes significantly as an associative bacterium to the nitrogen cycle in agriculture issues, even though in greenhouse experiments [17, 45, 46], X. autotrophicus strains isolated from several environmental samples have been shown to stimulate and growth yields of rice, tomato and lettuce at reduced dose of nitrogen or phosphate fertilizer [1, 17, 38, 47].

6.1 Ecological interactions with other domestic plants

In Japan was reported a survey of N2-fixing bacteria from roots of rice, with strains called group 2 were X. autotrophicus and other isolated Xanthobacter-like of group 5, which could be a new genus [22, 31, 48, 49]. Some of these isolations were identified as a X. flavus on the basis of morphological and physiological properties. Up to 25% of the nitrogen fixed by soil bacteria was incorporated into rice plants and other reported. In one soil like soils of Kasakh, Armenia Xanthobacter was up 40–70% were N2-fixing population they may contribute to N balance in the soil of paddy rice. Also was demonstrated that strains close to X. autotrophicus could be found in the sediment of patty rice fields in Arkansas, United States, with more than 105 cells per g dry weight of roots in the rhizosphere of rice clearly as an endophyte [50]. A positive interaction among Xanthobacter and some domestic crops due to enhance biomass of plant as well as nitrogen content compared to those crops without Xanthobacter at limited dose of nitrogen fertilizer [17, 40]. Therefore, Xanthobacter can be classified as an associative diazotroph [19, 38, 44, 51, 52]. The possible role of Xanthobacter as a contributor of fixed N2, a growth factor stimulant on bean [45] lettuce, tomato, rice, rootbeet, wheat, plants, and an associative N2 fixer through either the phyllosphere or even stems nodules if in the future Azorhizobium is incorporated into the genus Xanthobacter needs to be investigate [20, 41, 53]. These studies should examine: (1) the role of the slime produced by Xanthobacter in its adherence to the rhizosphere and phyllosphere an involvement of slime in adherence processes was shown for various anaerobic bacteria; (2) the possible role of the polyglutamine polymer produced under high-nitrogen conditions directly after nitrogen fertilization [7, 38, 54] and (3) the role of plant growth stimulant formation by root and stem-associated Xanthobacter cells [13, 28, 55, 56, 57]. It has been reported than cultures of X. autotrophicus are producing indoleacetic acid when grown in medium with tryptophan [3]. Until now there are no reports about Xanthobacter isolated associated with any plant disease [18].

6.2 Biofertilizer application of endophytic plant growth promoting bacteria in modern sustainable agriculture

Biofertilizer is key action of organic farming and a main element for the economy in general modern agricultural production on a world scale [55, 56, 58, 59]. The biofertilizers play an important role in improving the fertility of the soil [60, 61]. In addition, their application in soil improves the structure of the soil minimizes the sole application of chemical fertilizer. Grain yield and harvest index also increase with use of biofertilizers. Inoculation with Azotobacter + Rhizobium + mycorrhizae gave the highest increase in straw and grain yield of wheat plants with rock phosphate as a P fertilizer. Azolla is inexpensive, economical, friendly, which provide benefit in terms of carbon and nitrogen enrichment of soil [62]. Some commercially available biofertilizers are also used for the crop. Raj [63] recorded that microorganism: B. subtilis, Thiobacillus thioxidans, and Saccharomyces) can be used as bio-fertilizers for solubilization of fixed micronutrients like Zn (zinc). As well for biological control, a modern approach of disease management a key role in sustainable agriculture [64, 65, 66]. Biofertilizers can be defined as carriers that contain living endophytic plant growth promoting bacteria (EPGPB) and/or microorganisms (EPGPM); when they are applied to seeds, plant surfaces, to soil, or to hydroponic agricultural system, they colonize the root system or interior of the plant, and to stimulate plant growth by increasing the demanding or availability of macro or micro minerals: nitrogen (N), phosphorus (P), potassium (K), cupper (Cu), iron (Fe), etc., to the host plant [67, 68]. According to Mishra et al. [69], biofertilizer could be mixture of active or latent microbial cell for several important mechanisms to improve plant growth and yield as the well-known: nitrogen fixing, phosphate solubilizing, or cellulolytic microorganisms for applications to soil, seed, roots, or composting involving any microbial process with the aims for enhancing plant growth, augment the availability of nutrients that can then be easily absorbed by the plants, as well as for biological control of plant pathogenic agents. Malusá and Vassilev [70] proposed that a biofertilizer is the formulated product containing one or more microorganisms that enhance the mineral availability for health growth and yield profitable performance of the plants by either replacing soil nutrients and/or by making nutrients more available to plants and/or by increasing plant availability to basic minerals [66, 71].

Biofertilizer products are usually based on the EPGPB or PGPM can be classified into three main types of microorganisms: arbuscular mycorrhizal fungi or AMF [72], plant growth promoting rhizobacteria or PGPR [73], and nitrogen fixing rhizobia and free nitrogen fixing bacteria for non-leguminous plant [74, 75] which are applied and approved as beneficial for domestic crops growth based in mineral nutritional, underline reported that PGPR are recommend worldwide as biofertilizers, contributing to maintain profitable yield without soil deterioration and preventing environmental pollution. Hence, with the potential contribution of the PGPR, to sustainable agriculture and forestry when pandemic condition of COVID 19 caused economic world depress [76, 77]. Sufficient densities of PGPR and/or EPGPB like X. autotrophicus in biofertilizer provide a beneficial role in creating a proper rhizosphere for plant growth and converting nutritionally important elements through biological process, for example increasing the availability of N, P, K, as well as inhibiting pathogens growth [67, 71].

The increasing availability of N, P, and K is enhancing soil fertility, to improve antagonistic capacity of PGPR or EPGPB to biocontrol of plant pathogens agents [58] as well as the survival time in all types of soil [78]. Previous studies show that a biofertilizer prepared by mixing all types of PGPR with composts or carriers could enhance growth- promoting effects and biocontrol of plants [79]. Bacillus spp [80] and Pseudomonas spp [81] are two PGPR that have been reported to effective biocontrol agents. Among these bacteria species, Bacillus subtilis, B. amyloliquefacients, and B. cereus are the most effective species for controlling plant diseases in domestic crops by several mechanisms [82]. Due endospores of the genus and species of Bacillus are tolerant to adverse environmental conditions allows PGPR, to survive and even to grow in a wide range of soils, thus facilitating the effective formulation of biofertilizer [83]. Based in this biochemicals qualities as well as the biorestauration of hyper fertilized or deteriorated soil [43, 74, 84, 85]. However, X. autotrophicus has many biological mechanisms to avoid environmental stress without any specific resistance structure a quality of this genus and specie [3, 21, 35] that has been useful to treat environments contaminated by chemical agents [86].

6.2.1 Biofertilizer (X. autotrophicus) for bioremediation of environment polluted by chemical agents

In that sense EPGPB (likes PGPM or/and PGPR can be classified as biofertilizers when they sustainable options to plant nourishment and enrichment source that would useful for bioremediation and/or phytoremediation (double actions plants and biofertilizer) for soil contaminated by chemical agents [87, 88]. There for X. autotrophicus is has been applied in bioaugmentation trials for cleaning up any environmental impacted by chemical agents [86] which due to powerful genetic capacity is able to degradate a wide range of chemical agents under several environmental conditions either soil and or water in that sense it been reported that X. autotrophicus is able to biodegradate of 1,2- dichloroethane (DCE) one of the largest chlorinated industrial chemical, most of it being used for synthesis of vinyl chloride and smaller amounts for ethylene diamine and other chemicals. It was also used as a solvent. Groundwater contamination is mainly due to leakages and improper waste disposal. X. autotrophicus can attack DCE by using some specific enzimes under oxic conditions was investigated in the 1980s [89, 90] required for prolonged groundwater bioremediation polluted by DCE. Such systems are operated under non-sterile conditions, and long-term survival of enzymes would require separate enzyme production and a process allowing for physical separation of the biocatalyst from groundwater. There may be attractive application opportunities if biotransformation of synthetic chemicals in waste streams leads to products that can be recycled, e.g., when a wastewater product can cleaning up. This issue that received attention during the development of strains of X. autotrophicus growing on 1,2,3-trichloropropane (TCP) and another xenobiotic compound that polluted wastewater [86, 90, 91, 92].

A bioformulation is not effective until it does not have an impact in field conditions, market existence and reliability and cost effectiveness [93]. Production of bioformulation is not only dependent on the detailed knowledge of microbial as well as plant physiology, but a number of technological challenges are also involved such as fermentation process, formulation type, population of microbe, and delivery systems [94]. Barea [59] has published that in order to get better bioformulation for any domestic crops is important to understand the interaction among EPGPB or PGPM. To reproduce those microorganisms is important the chemical composition of broth media as well as the main and best conditions for each microorganisms need to get enough amount of them for bioformulation applying in open agriculture [95]. Including legal and ecological permission for safe crops production. A key quality of any bioformulation has to be water soluble to make sure a positive effect on any domestic crop Himel et al. [96] and Bateman [97] underline for those bioformulation which are applying in in aerosol based on a droplet size that is sufficient to inoculate seeds and plants with excellent results. For bioformulations applied foliarly, it is important to consider all environmental factors: solar radiation, high temperatures, ultraviolet light, etc. that limit the survival of beneficial plant microorganisms [98]. In this sense, the type of bioformulations must be appropriate to the form and vehicle that transport the beneficial plant microorganisms according to the recommended application directly to the soil, to the seeds or plants so that the forecast of the result favors agricultural production or control of some disease or pest [99]. Therefore, it is important research for the innovation of bioformulation suitable for agricultural crops [58] that comply with the quality and legality standards to satisfy the world market demand for safe food without risk of environmental damage [100]. A fundamental aspect for the world market of biological inoculants has been the necessary implementation of microbiological quality controls with reliable protocols that are endorsed by laws in the world that protect those farmers who, when applying them, have the confidence that they will have positive results in production. agriculture, due in part to the unfortunate experience of bioformulations without microbiological or legal quality that have caused a rejection of some sectors involved in sustainable agricultural production, an aspect that has not yet been resolved in the world [68]. In an integral sense that the biotechnology of the formulation of inoculants requires solid research for the best selection of microorganisms that promote plant growth, as well as the protocols of legal and ethical microbiological quality in the generation of bioformulations that give confidence to be used in the world for a sustainable and harmless agricultural production in harmony with the environment [85].


7. Effect of Xanthobacter autotrophicus on the growth of Triticum aestivum and other domestic plants

Triticum aestivum is the main cereal consumed by the human population of the world, around 51% of human demand intake of calories and proteins. The annual production of this crop is ~630 million tons, being the major grown cereal worldwide with ~740 million ha harvested annually [101]. It is reported that the dynamics of colonization of endophytic genus plant growth promoting bacteria (EPGPB) like X. autotrophicus on the sphermosphere/rhizosphere in gramineae is reported, based in other genera and species different than Xanthobacter [49, 102, 103]. In that sense the response of domestic plants to X. autotrophicus is scarce [18] so research in progress indicates [16, 17, 45, 46] that it may be an excellent option for the sustainable production of domestic crops [67, 104, 105, 106] however it is believed that it may be similar to other genera and species of EPGB, of the known like Azospirillum, Azotobacter, Bacillus which are able to move from outside to into the root system [18, 107]. In the case of T. aestivum has a positive response to X. autotrophicus since can invade the interior of the root system where it transforms organic compounds derived from photosynthesis into phytohormons, to optimize the reduced dose of nitrogen fertilizer [46]. It has been showed that can invade the root of T. aestivum including other types of domestic crops [17, 45, 60]. This biochemical characteristic of X. autotrophicus was confirmed by its growth dependent on the nutritional richness of the rhizosphere of T. aestivum, attributable to certain organic acids, amino acids including other organic compounds from the photosynthesis in gramineae [42, 108]. Hence, the importance of the chemical composition of root, sphermosphere and rhizosphere, as inducers of colonization by X. autotrophycus in gramineae, is key for other EPGPB to be closely associated with its root, sphermosphere, rhizosphere system [60, 105, 109]; in part this also explains the nutritional requirement of X. autotrophicus for wheat as a distinctive characteristic of this species, which is not reported in X. autotrophicus this was verified when was inoculated in the soil without roots, this coupled with the competition and predation of the native soil microorganisms, antagonistic to the species of Xanthobacter, which prevented its persistence in that environment [20, 47]. In the literature it is reported that the positive response of T. aestivum to inoculation with X. autotrophicus and fed with NH4NO3 depends on fast they colonized exclusively the germination zone of the seed, as well as to invade inside the roots when they have developed [41, 109, 110]. This explains why, in the case of the test described, X. autotrophicus was detected during seed germination, in the period of root development, and even inside mature roots of wheat. This suggests that X. autotrophicus was not dependent on wheat’s sphermosphere/rhizosphere [17, 108, 109], it is reported that slowly used its energy reserve to prolong its persistence in unsterilized soil, a physiological characteristic in X. autotrophicus [111, 112]. These results support that T. aestivum were attractive for X. autotrophicus used according to the type of root growth observed with T. aestivum, compared to the appearance of the root system in the coronary part and by the density of secondary roots detected uninoculated wheat [37, 46, 47, 113, 114].

Related to phosphorus a key mineral for plant nutrition as phosphates normally applied to soil as fertilizer it is reported that concentration in average soils is about 0.05% (w/w) of which only 0.1% is available to plants [115]. There is evidence that the phosphate fertilizer applied as phosphate has a limited impact on plant nutrition, especially because, due to the solubilization constant (Ksp), of this phosphate anion is generally little available for plant roots [116]. It is calculated in the soil the concentration of phosphorus as phosphates is equal to or less than 0.02ppm, which drastically limits plant growth [117, 118]. In nature, the strategy that plants use for the absorption of the forms of phosphates necessary for plant metabolism are the solubilization actions of phosphates by genera and species of microorganisms that promote plant growth, such as mycorrhizae and bacteria that also mineralize organic compounds containing phosphates [119, 120]. In the last few years, the development of microbial inoculum containing phosphate-solubilizing microbes (PSM) gained attention of agriculturists [17].

Figure 3 shows the positive response of T. aestivum to X. autotrophicus fed at 50% of NH4NO3 and 100% phosphate fertilizer. Figure 3c shows that T. aestivum reached a greater number of leaves and a dense root system, as well as T. aestivum with X. autotrophicus fed with 100% nitrogen fertilizer and 50% phosphate fertilizer (Figure 3d) and T. aestivum with X. autotrophicus fed with 50% nitrogen and phosphate fertilizer (Figure 3e), compared to T. aestivum not inoculated irrigated with water (Figure 3a) and T. aestivum not inoculated fed with 100% nitrogen and phosphate fertilizer (Figure 3b). These facts indicates that X. autotrophicus transformed the organic compounds from photosynthesis of T. aestivum into root system to improve root absorption and optimize the reduced dose of nitrogen fertilizer without risk to plant health growth [17, 18, 38, 42, 43, 121, 122]. At the same time the synthesis of acid and mainly alkaline phosphatases improved the solubilization and absorption of soil phosphates and phosphate fertilizer apply [17, 123, 124] to enhance growth plant (data not showed). In Figure 1 it was evident that X. autotrophicus is an excellent option for the sustainable production of T. aestivum since it is not only capable of optimizing nitrogen fertilizer to avoid soil deterioration and environmental contamination due to nitrogen hyperfertilization [36, 54, 121, 125, 126]. While T. aestivum inoculated with X. autotrophicus simultaneously absorbs the immobilized phosphate from the soil and optimizes the effective application from the inside of its roots by avoiding competition with the native microorganisms [13, 40, 53] with a high prognosis of achieving healthy growth and profitable yield [43, 122]. In that sense Khalid et al. [127] reported that seed inoculation with 30 bacterial strains isolated from rhizospheric soils of wheat plants cultivated at different sites significantly increased length and weight of wheat roots and shoots. Linear positive correlation between in vitro auxin production by these bacteria and increases in the measured growth parameters was observed. Abd El-Azeem et al. [128] reported a highly significant positive linear correlation between the in vitro auxin production by the tested PGPR strains and each of grain yield, straw and total yield (grain plus straw) as well as the number of tillers of wheat plants. Auxin or indole acetic acid (IAA) production is considered a way in which X. autotrophicus promotes plant growth by stimulating enzymological reactions [125, 129]. IAA influences plant processes, such as initiation of cell division and promotes vascular differentiation [130, 131]. Besides its hormonal functions, IAA is involved in the stimulation of ethylene synthesis, which is produced, by plants and microorganisms [47]. Ethylene plays several active roles in plants including germination of root and shoot and the response of plants to stress [43]. There is an evidence that X. autotrophicus that solubilize phosphate in soil and promote its uptake by plants are referred as phosphate solubilizing bacteria (PSB) or phosphobacteria and are included within EPGPB [132]. Plant growth promoting rhizobacteria increase the efficiency of fertilizers while reducing nitrogen loss. Their counts in the rhizosphere comprise a considerable share of the rhizospheric microorganisms and vary depending on the soil location and type as well as the cultivated plants [133]. Inoculating the soil or seeds with PSB individually or in combination with other microorganisms, especially the nitrogen-fixing bacteria increased the availability of P, Fe, Mn, Zn and Cu for plants and consequently increased crop yield [114, 134, 135].

Figure 3.

Response of Triticum aestivum to Xanthobacter autotrophicus at different levels of nitrogen and phosphate fertilizer at seedling stage 30 days after sowing. (a) Absolute control: T. aestivum not inoculated irrigated only with water; (b) relative control: T. aestivum not inoculated fed at 100% nitrogen and phosphate fertilizer; (c) T. aestivum with X. autotrophicus fed with 50% of nitrogen fertilizer and 100% phosphate fertilizer; (d) T. aestivum with X. autotrophicus fed with 100% nitrogen fertilizer and 50% phosphate fertilizer; (e) T. aestivum with X. autotrophicus fed with 50% nitrogen and phosphate fertilizer.

Figure 4 shows the positive response of Z. mays to X. autotrophicus fed with 50% nitrogen fertilizer and 100% phosphate fertilizer (Figure 4c), had the highest number of leaves, plant height and the highest root density, as well as Z. mays with X. autotrophicus fed with 100% nitrogen fertilizer and 50% phosphate fertilizer (Figure 4d) and Z. mays with X. autotrophicus fed with 50% nitrogen and phosphate fertilizer (Figure 4e), compared to Z. mays not inoculated irrigated only with water (Figure 4a) and Z. mays not inoculated fed with 100% nitrogen and phosphate fertilizer (Figure 4b). Figure 2 shows the effect of X. autotrophicus on the healthy growth of Z. mays at different doses of nitrogen and phosphorous fertilizer, supporting that X. autotrophicus from the interior of the root system of Z. mays had the ability to convert compounds generated from photosynthesis in phytohormones for the optimization of the fertilizer reduced to 50%, simultaneously with an increase in the acid and alkaline phosphatase activity for the solubilization of the immobile phosphates of the soil and the optimization of the phosphate fertilizer also reduced 50% [17, 44, 45, 47, 106, 131] compared to the limited growth of Z. mays without inoculation with X. autotrophicus where the absence of this endophytic bacterium that promotes plant growth shows that Z. mays that none of these fertilizers is efficiently absorbed, causing loss of soil fertility and a possible environmental contamination [43].

Figure 4.

Response of Zea mays to Xanthobacter autotrophicus at different levels of nitrogen and phosphate fertilizer at seedling stage 15 days after sowing. (a) absolute control: Z. mays not inoculated irrigated with water; (b) relative control: Z. mays not inoculated fed with 100% nitrogen and phosphate fertilizer; (c) Z. mays with X. autotrophicus fed with 50% nitrogen fertilizer and 100% phosphate fertilizer; (d) Z. mays with X. autotrophicus fed with 100% nitrogen fertilizer and 50% phosphate fertilizer; (e) Z. mays with X. autotrophicus fed with 50% nitrogen and phosphate fertilizer.

In Figure 5, showed the response of O. sativa to X. autotrophicus by the root length and plant height of O. sativa at 50% nitrogen fertilizer as NH4NO3 and 100% phosphorous fertilizer as K2HPO4/KH2PO4 (Figure 5c), in comparation to O. sativa with the maximum dose of nitrogen and phosphorous fertilizer but without X. autotrophicus (Figure 5b), as well as O. sativa with X. autotrophicus fed with 50% nitrogen and phosphate fertilizer (Figure 5e). This support that X. autotrophicus h is able to transform organic compounds from photosynthesis into phytohormons like auxins to increase root soil exploration for optimizing uptake of nitrogen fertilizer reduced to 50% [18, 45, 46, 106]. There is evidence that to support that X. autotrophicus in wheat, as well as in, oats, corn, sorghum, and other types of plants the way do other genus and species of growth plant promoting bacteria. While inside the roots of O. sativa; X. autotrophicus synthesizes acid and alkaline phosphatases for the solubilization and absorption of insoluble phosphate from the soil, as well as optimizing the phosphate fertilizer applied to the soil at a reduced dose without affecting the healthy growth of O. sativa compared to the response of O. sativa without inoculating with X. autotrophicus fed with the recommended dose of nitrogen and phosphate fertilizer, which shows that without the help of X. autotrophicus, O. sativa has growth limitations, therefore it is advisable to apply it to the sowing of the seed [119, 120, 123, 124, 126]. While inside the roots of O. sativa; X. autotrophicus synthesizes acid and alkaline phosphatases for the solubilization and absorption of insoluble phosphate from the soil, as well as optimizing the phosphate fertilizer applied to the soil at a reduced dose without affecting the healthy growth of O. sativa compared to the response of O. sativa without inoculating with X. autotrophicus fed with the recommended dose of nitrogen and phosphate fertilizer, which shows that without the help of X. autotrophicus; O. sativa has growth limitations, therefore it is advisable to apply it to the sowing of the seed [46, 106, 136].

Figure 5.

Positive response of Oryza sativa to Xanthobacter autotrophicus at different levels of nitrogen and phosphate fertilizer at seedling stage 15 days after sowing. (a) Absolute control: O. sativa not inoculated irrigated with water; (b) relative control: O. sativa not inoculated fed with 100% nitrogen and phosphate fertilizer; (c) O. sativa with X. autotrophicus fed with 50% nitrogen fertilizer and 100% phosphate fertilizer; (d) O. sativa with X. autotrophicus fed with 100% nitrogen fertilizer and 50% phosphate fertilizer; (e) O. sativa with X. autotrophicus fed with 50% nitrogen and phosphate fertilizer.

In Figure 6, L. sativa inoculated with X. autotrophicus fed with 25% nitrogen and phosphate fertilizer (Figure 6e), as well as L. sativa with X. autotrophicus fed with 25% nitrogen fertilizer and 100% phosphate fertilizer (Figure 6d), had the highest number of leaves, plant height and the highest root density, compared with L. sativa not inoculated fed with 100% nitrogen and phosphate fertilizer (Figure 6b). It is reported that X. autotrophicus stimulated the proliferation of root hairs in wheat, as has been observed in other plants [17, 41, 44, 137, 138] and this increased the area of exploration of the root to capture the nitrogen and phosphate fertilizer [42], as reported in other works on X. autotrophycus inoculation: in corn [46, 106], in wheat and in rice [43, 139].

Figure 6.

Response of Lactuca sativa to Xanthobacter autotrophicus at different levels of nitrogen and phosphate fertilizer at flowering stage 120 days after sowing. (a) Absolute control: L. sativa not inoculated irrigated with water; (b) relative control: L. sativa not inoculated fed with 100% nitrogen and phosphate fertilizer; (c) L. sativa with X. autotrophicus fed with 100% nitrogen fertilizer and 25% phosphate fertilizer; (d) L. sativa withX. autotrophicus fed with 25% nitrogen fertilizer and 100% phosphate fertilizer; (e) L. sativa with X. autotrophicus fed with 25% nitrogen and phosphate fertilizer; (f) L. sativa with X. autotrophicus fed with 0% nitrogen and phosphate fertilizer.

Figure 6 shows the effect of X. autotrophicus on the growth of L. sativa at different doses of nitrogen and phosphate fertilizer, where it was evident that X. autotrophicus can optimize the reduced dose of both fertilizers, in relation to nitrogen fertilizer by means of a conversion of metabolites released during photosynthesis [10, 17, 138], that reach the root to maximize the absorption of NH4NO3 while X. autotrophicus from inside the roots generates acid and especially alkaline phosphatases to solubilize the immobile phosphate of the soil, as well as optimize phosphate applied during the growth of L. sativa [140], in this trial it was demonstrated that these were the main mechanisms of X. autotrophicus when both fertilizers were applied in variable doses or in similar concentration, but not when in the absence of both [18, 120, 123, 124].

The possible synthesis of phytohormons by X. autotrophicus was supported by the test shown in Figure 7, in which it is evidenced by inoculation of S. lycopersicum with X. autotrophicus fed with 25% nitrogen and phosphate fertilizer (Figure 7e), had the highest number of leaves, fruits, plant height and the highest root density, compared to S. lycopersicum not inoculated fed with 100% nitrogen and phosphate fertilizer (Figure 7b). The positive growth of S. lycopersicum was due to the fact that X. autotrophicus had a growth promoter effect, which was detected from the beginning of wheat germination from its seed, reported to be maintained in the early stages of wheat root development [20, 41, 50], as observed in this experiment and which was similar to what was observed in root system when X. autotrophicus it colonizes and influences the growth of roots of beans [45, 54]. In that sense Figure 7 shows the effect of X. autotrophicus on S. lycopersicum at different doses of nitrogen (NH4NO3) and phosphate (KH2PO4/K2HPO4) fertilizer, the growth of S. lycopersicum shows that the ability of X. autotrophicus to invade the interior of the radical system to transform compounds derived from photosynthesis into phytohormons improves the absorption and optimization of the reduced doses of NH4NO3 [13, 14, 15, 126] as well as of phosphorous fertilizer, and even when none of them were applied to the crop is reported that N demand was supplied by biological N2 fixation due to X. autotrophicus [18, 36, 52] it was also detected that it synthesized acid and alkaline phosphatase to solubilize the immobile of the soil, so that S. lycopersicum had a healthy growth with early formation of fruits [16, 17, 120, 135, 140] compared to S. lycopersicum without inoculating fed with the recommended doses both fertilizer.

Figure 7.

Response of Solanum lycopersicum to Xanthobacter autotrophicus at different levels of nitrogen and phosphate fertilizer at maturity stage 180 days after sowing. (a) Absolute control: S. lycopersicum not inoculated irrigated with water; (b) Relative control: S. lycopersicum not inoculated fed with 100% nitrogen and phosphate fertilizer; (c) S. lycopersicum with X. autotrophicus fed with 100% nitrogen fertilizer and 25% phosphate fertilizer; (d) S. lycopersicum with X. autotrophicus fed with 25% nitrogen fertilizer and 100% phosphate fertilizer; (e) S. lycopersicum with X. autotrophicus fed with 25% nitrogen and phosphate fertilizer; (f) S. lycopersicum with X. autotrophicus fed with 0% nitrogen and phosphate fertilizer.

Table 2 shows the acid and alkaline phosphatase activity of X. autotrophicus, measured indirectly by the amount of p-nitrophenol generated when measured in the stem and roots of S. lycopersicum (as it is a genus and endophytic growth plant promoting species) with nitrogen and phosphorous fertilizers at 25%, of the recommended dose, there it is observed that the values of the higher and lower acid phosphatase of the alkaline support that the healthy growth of the vegetable was due to the activity of the phosphatases synthesized by X. autotrophicus not only the interior of the stem and better in the root, also when this strain of X. autotrophicus recovered from the stem as well as from the root results suggest the importance of soil phosphorus availability in altering the interactions between leading to soil invasion by S. lycopersicum by X. autotrophicus. Overall, applying high amounts of available nutrients may reduce and increase the abundance plant-beneficial microbes and pathobiome in soil, respectively, which in return, could affect soil and plant health. This work greatly advances the mechanistic understanding why X. autotrophicus is a genus with high competitive capacity within the broad group of growth-promoting endophytes that synthesize acid and/or alkaline phosphatases in the absence of available phosphates and even when soluble phosphates fertilizer is applied to soil in agricultural production [141], that issue could be important for researchers working in the field of environmental microbiology, microbial ecology, plant-microbe interactions, soil health, and plant protection [16, 17, 18, 123, 142] in comparison with the activity of both phosphatases of S. lycopersicum without inoculation with X. autotrophicus, where the poor activity of both phosphatases explains that the growth of this vegetable was not as vigorous as observed in S. lycopersicum inoculated with X. autotrophicus [120, 136]. Similar results of a high acid and alkaline phosphatase activity of X. autotrophcius inside the roots: Beta vulgaris, Hordeum vulgare, Pinus leiophylla, T. aestivum, Sorhgum bicolor. Z. mays, grown in soil with insoluble phosphate problems [124, 135, 137, 143] or precipitation of the phosphate fertilizer at a lower dose than recommended (data no shown).

S. lycopersicum (tomato)*p-nitrophenol released (μg/ mL)
Saline solution (absolute control)Acid
Without inoculating stemAcid0.45f**
Without inoculating rootAcid1.49e
X. autotrophicus on the stemAcid140.22c
X. autotrophicus on the rootAcid222.48a
X. autotrophicus isolated from the stemAcid139.77c

Table 2.

Activity of acid and alkaline phosphatases of Solanum lycopersicum at flowering stage 120 days after sowing at 25% of nitrogen and phosphate fertilizer with and without inoculating with Xanthobacter autotrophicus.

n = 3.

Values with different letter are stadistically distint according to ANOVA-Tukey (P < 0.05).

Figure 8 shows that fruit of S. lycopersicum with X. autotrophicus fed with 100% nitrogen fertilizer and 25% phosphate fertilizer had the largest size and red coloration (Figure 8) while S. lycopersicum not inoculated irrigated fed with 100% nitrogen and phosphate fertilizer had a smaller size, in addition to a green coloration which means that vegetative life cycle was shorter than the fruit from not inoculate S. lycopersicum (Figure 8a). These results demonstrate the importance of X. autotrophicus for healthy growing plants, with a reduced dose of nitrogen and phosphorous fertilizer [54, 120, 144, 145]. Figure 8 shows the effect of X. autotrophicus on the fruit of S. lycopersicum at a recommended dose of nitrogen fertilizer such as NH4NO3 with 25% of the phosphate fertilizer, in that sense X. autotrophicus is able to solubilize phosphate in soil and promote its uptake by plants are referred as phosphate solubilizing bacteria (PSB) or phosphobacteria and are included within PGPR [143]. Their counts in the rhizosphere comprise a considerable share of the rhizospheric microorganisms and vary depending on the soil location and type as well as the cultivated plants [133, 142, 146]. The results support that X. autotrophicus transformed organic compounds derived from photosynthesis in the inside the roots of S. lycopersicum in phytohormons for an efficient absorption of NH4NO3 while to optimize the phosphate fertilizer, X. autotrophicus by means of acid phosphatases, mainly alkaline phosphates solubilized the soil phosphates [123, 124, 142, 143, 145] and quickly absorbed the one applied consequently the fruit of the S. lycopersicum reached a larger size and ripened earlier in comparison with the size of the S. lycopersicum without inoculation fed with the recommended dose of both fertilizers [14, 16, 17, 38, 43, 50, 144].

Figure 8.

Fruit of Solanum lycopersicum with Xanthobacter autotrophicus at different levels of nitrogen and phosphate fertilizer at maturity stage 180 days after sowing. (a) Relative control: S. lycopersicum not inoculated fed with 100% nitrogen and phosphate fertilizer; (b) S. lycopersicum with X. autotrophicus fed with 100% nitrogen fertilizer and 25% phosphate fertilizer.

Figure 9 shows that A. thaliana with X. autotrophicus fed with 100% NH4NO3 (Figure 9d), as well as A. thaliana with X. autotrophicus fed with 50% NH4NO3, (Figure 9h) and A. thaliana with X. autotrophicus irrigated with only water (Figure 9l) had root growth inhibition, its suggested due over synthesis of phytohormons not depending of NH4NO3 concentration [20, 79, 99, 131, 147] compared to A. thaliana with B. vietnamiensis 2 fed with 100% NH4NO3 (Figure 9c), as well as A. thaliana not inoculated fed with 50% NH4NO3 (Figure 9e) and A. thaliana not inoculated irrigated with water (Figure 9i).

Figure 9.

Response of Arabidopsis thaliana to Burkholderia vietnamiensis and Xanthobacter autotrophicus on the germination of seed and first step of growth at seedlings stage at different dose of NH4NO3 under artificial culture media. (a) A. thaliana not inoculated fed with 100% NH4NO3; (b) A. thaliana with B. vietnamiensis 1 fed with 100% NH4NO3; (c) A. thaliana with B. vietnamiensis 2 fed with 100% NH4NO3; (d) A. thaliana with X. autotrophicus fed with 100% NH4NO3; (e) A. thaliana not inoculated fed with 50% NH4NO3; (f) A. thaliana with B. vietnamiensis 1 fed with 50% NH4NO3; (g) A. thaliana with B. vietnamiensis 2 fed with 50% NH4NO3; (h) A. thaliana with X. autotrophicus fed with 50% NH4NO3; (i) A. thaliana not inoculated irrigated with water; (j) A. thaliana with B. vietnamiensis 1 irrigated with only water; (k) A. thaliana with B. vietnamiensis 2 irrigated with water; (l) A. thaliana with X. autotrophicus irrigated with only water.

Figure 10 shows that A. thaliana with X. autotrophicus fed with 100% NH4NO3 (Figure 10d), as well as A. thaliana with X. autotrophicus fed with50% NH4NO3, (Figure 8h) and A. thaliana with X. autotrophicus irrigated with water (Figure 10l) had root growth inhibition, compared to A. thaliana with B. vietnamiensis 1 fed with 100% NH4NO3 (Figure 10b), as well as A. thaliana with B. vietnamiensis 1 fed with 50% NH4NO3 (Figure 10f) and A. thaliana with B. vietnamiensis 1 irrigated with water (Figure 10j). Figures 9 and 10 show the response of the seed and stem primordia and root of A. thalina inoculated with B. vietnamiensis compared to X. autotrophicus at doses 100, 50 and 0% of the nitrogen fertilizer as NH4NO3 where it was evident that while a positive effect of B. vietnamiensis strains on A. thaliana was dependent on the concentration of NH4NO3, [41, 110, 129, 148] X. autotrophicus inhibited seed germination and practically stem and root primordium, both effects were positive by B. vietnamiensis well-known plant beneficial bacteria for a domestic vegetal [149]. In opposite way X. autotrophicus can distinguish between a domestic plant and a weed planted in agricultural soil by stimulating the growth of the former and inhibiting the germination and growth of the latter [150]. A genetic capacity that few genera and species such as X. autotrophicus of growth-promoting endophytic bacteria possess and can be used to improve the growth of domestic plants and prevent the germination of weeds underline when they are dependent on the synthesis of phytohormons from compounds releasing of the seed and roots of A. thaliana [46, 47, 59, 79, 131, 147].

Figure 10.

Effect of Burkholderia vietnamiensis and Xanthobacter autotrophicus on the germination of seed and first step of growth of Arabidopsis thaliana seeds directly sown in inoculated in artificial culture media at different dose of nitrogen fertilizer as NH4NO3. (a) A. thaliana not inoculated fed with 100% NH4NO3; (b) A. thaliana with B. vietnamiensis 1 fed with 100% NH4NO3; (c) A. thaliana with B. vietnamiensis 2 fed with 100% NH4NO3; (d) A. thaliana with X. autotrophicus fed with 100% NH4NO3; (e) A. thaliana not inoculated fed with 50% NH4NO3; (f) A. thaliana with B. vietnamiensis 1 fed with 50% NH4NO3; (g) A. thaliana with B. vietnamiensis 2 fed with 50% NH4NO3; (h) A. thaliana with X. autotrophicus fed with 50% NH4NO3; (i) A. thaliana not inoculated irrigated with water; (j) A. thaliana with B. vietnamiensis 1 irrigated with water; (k) A. thaliana with B. vietnamiensis 2 irrigated with water; (l) A. thaliana with X. autotrophicus irrigated with water.


8. Conclusions

The plant growth promoting endophytic bacteria well known as X. autotrophicus is an exceptional genus and species of procaryote due to the ability it has to simultaneously fix CO2 and N2, it can exist in water, soil and in association with a wide variety of plant species, specifically because by invading the root tissue it influences positively in the absorbing both nitrogen and phosphorous regulated forms of fertilization by the synthesis of acid and alkaline phosphatases in soil with phosphate availability problems or where the application of the phosphate fertilizer precipitates. Whereas by converting seed exudates and derivates and photosynthesis inside the root’s plants in phytohormons have an interesting potential as a biofertilizer. As well as for the biological control of weeds that compete with the cultivation of domestic plants, it can contribute to sustainable agricultural production that reduces the effects of contamination by unregulated fertilization and application of chemical herbicides. Besides that X. autotrophicus is has been reported as useful biological tool for bioremediation of water and soil polluted by chemical agents. Easy to growth in simple culture media low cost to reproduce to industrial level, a friendly genus and bacterial species for humans, animals, plants and the environment.



The support of project 2.7 (2021-2022) of the Coordination of Scientific Research of the UMSNH, Morelia, Michoacan, Mexico is appreciated. As well as the project: “Field Test of a Living Biofertilizer for Crop Growth in Mexico” from Harvard University, Cambridge, Ma, USA with funding from the Rockefeller Foundation (2019–2022). To Jeaneth Caicedo Rengifo for her help working in this project. To Juan Luis Ignacio de la Cruz, MSc Blanca Celeste Saucedo Martinez and J Alberto Castro-Villaseñor for their technical support.


Conflict of interest

The authors declare no conflict of interest.


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Written By

Juan Manuel Sánchez-Yañez

Submitted: 07 October 2021 Reviewed: 17 December 2021 Published: 23 March 2022