Pseudomonas aeruginosa is considered as the most potent bacterial strain for solving heavy metals pollution problems. Pollution is the most of problems in our world which causing a lot of risks to human, animal, plant and ecosystem. Heavy metals pollution is an ever-increasing problem in developing nations. Release of heavy metals into the environment has increased in the recent years at an alarming rate. To remove heavy metals from environment, there are different methods such as physical, chemical and biological. The biological method includes microorganisms and plant which recorded high heavy metals removal, safe and low-cost method. Microorganisms remove heavy metals from environment by different mechanisms according to their types. Thus, microbes are used as potential candidates of bioremediation that can adapt quickly to the changing noxious environment and be utilized for toxic metal remediation. In bacterial uptake and tolerance to heavy metals, Pseudomonas aeruginosa recorded potential role in bioremediation of different heavy metals with high removal percentage comparison with other bacterial strains. Chapter discusses the roles and trends of Pseudomonas aeruginosa in heavy metals tolerance and uptake as potential bacterial strain.
- Pseudomonas aeruginosa
- heavy metals
- plasmid and resistant genes
Heavy metals are wide distribution elements in environment have a high density, atomic weight and multiple applications in different fields . Heavy metal pollution causes environmental problems to human, animal, plant and ecosystem . This pollution resulted in accumulation of different heavy metals in to soil and water. Different heavy metals such as copper, cadmium, nickel, lead, chrome and mercury, etc. released into natural sources and recorded high accumulation then have toxic effects on human health and biological system .
To remove of this heavy metals, there are different biotechnological methods were done such as bio-mineralization, bio-sorption, phyto-stabilization, hyper-accumulation, bio-stimulation, rhizo-remediation, myco-remediation, cyano-remediation and geno-remediation .
In nature, microorganisms play a potential role for a recycling and degradation of accumulated heavy metals which decrease their toxicity. This microorganisms as fungi, bacteria and algae were recognized . Also, bioremediation of heavy metals by microorganisms is an economic and effective strategy because of its high efficiency, low cost and eco-friendly nature. Additionally, microbial bioremediation is done by interaction of microbe-metal for accumulation and detoxification of heavy metals .
Subsequently, some of bacterial strains can remove heavy metals from polluted soils as
2. Problems and risks of heavy metals on environment
2.1 Heavy metals pollution sources
Firstly, pollution of environment is a huge problem in the world because of increasing of industrial activities resulting the toxic compounds which lead to contamination of soils and clean water . Toxic heavy metals pollution is a wide distribution throughout world countries along with progress of different industries which chromium, copper, nickel cadmium and mercury were observed as the most common heavy metals that widespread and used causing environmental pollution . Increased industrial activity and demand for heavy metals like arsenic, nickel, chrome, copper, lead, mercury, manganese, zinc cadmium and many more has recorded increasing in amounts of heavy metals at polluted wastewater . Additionally, metallurgical and mining industries are generated high amounts of heavy metals in wastewaters and accumulate in soil and water. . Also, agricultural activities using pesticides, fertilizers and crop preservatives which participate in releasing of heavy metals in to the environment .
2.2 Heavy metals effects on living organisms
Heavy metals are any inorganic metallic compound that can exert their toxicity via binding to the thiol group of the enzyme and the disulfide bond that contribute the stability of the enzyme. The metals have high affinity to the disulfide bridge between two cysteine residues in any protein compound. Heavy metals are very dangerous to living organisms especially human as certain of them cause DNA damage and their carcinogenic effects in animals and man are probably causally related to their abilities to cause mutation . Also, heavy metals divided into nonessential metals (lead, cadmium, mercury and nickel) and essential metals (zinc, copper, iron and manganese). Because of their high toxicity, lead and cadmium represented the major heavy metals pollutants. Cadmium is released to ecosystem during electroplating, effluents from textile, mine tailing, tannery, leather, and galvanizing industries (cadmium batteries) . Due to their high prevalence as contaminants, heavy metals have an excellent concern to environmental problems in soluble type that area unit terribly venomous to biological systems causing cancer . Also, heavy metal compounds in soluble forms might be harmful for living organisms of ecosystem by entering of the food chain .
In 2015, ATSDR prepared the priority list of hazardous substances and the results recorded that cadmium and lead were in the seventh position and second position, respectively. Also, The International Agency for Research on Cancer classified cadmium and cadmium compounds as a group (1) carcinogen and lead compounds as group (2) carcinogens . Additionally, cadmium cause renal dysfunction especially in the proximal tubular cells which considered as the main site accumulation of cadmium. Also, cadmium cause demineralization of bone either indirectly, as a result of renal dysfunction or directly by the bones damaging. Furthermore, nickel has carcinogenic, neurotoxic, hemato-toxic, reproductive toxic, immune-toxic, genotoxic, nephrotoxic, pulmonary toxic and hepatotoxic effects . On the other hand, mercury cause risks effects as neurotoxic substance because it accumulates and increase its content in food chains .
Subsequently, if plants exposure to excess copper concentrations, it generates oxidative stress causing damage to macromolecules and metabolic pathways disturbance. Also, excessive manganese accumulates in leaves and causing photosynthetic rate reduction . Plants can uptake high concentration of heavy metals that present in causing adversely effect of symbiosis, the growth and consequently effects on the crops yields .
In addition, chromium (hexavalent form) is the most toxic chromium species which used in some industries as leather processing. Chromium is a carcinogenic substance especially in case of the lung and enter through inhalation. Chromium toxicity comes from its potentiality to cause allergic reactions and be corrosive .
Furthermore, heavy metals effect on microorganisms and induced physiological and morphological changes in microbial populations . When microorganisms exposed to heavy metal stress, they produce antioxidant enzymes under toxic conditions and tolerance of this stress such as some resistant bacterial strains . In naturally, microbes response to toxicity of heavy metals depends on high concentration and its resistance and tolerance mechanisms .
3. Bioremediation of heavy metals by microorganisms
Bioremediation meaning use of microbial metabolism to remove of pollutants. It can occur on its own and this called intrinsic bioremediation or can be done by addition of fertilizers to stimulate of microbial bioavailability inside medium and this called bio stimulation. Also, in some cases the addition of other microbial strains into medium to enhance the resident microbial population’s and increase their ability to remove of heavy metals. Microorganisms that used to perform this function of bioremediation known as bio-remediators . These microorganisms have developed unique resistance mechanisms which allowing to survive and remove high concentrations of heavy metals from environments . Subsequently, bioremediation considered as alternative to chemical techniques by using microorganisms for biodegrading and detoxify of heavy metals from polluted soils and wasted groundwater .
In addition, biosorption defined as the use of biomass to remove heavy metals from environment by using microorganisms as (bacterial strains, fungal strains and algae) or plant extracts. It represents as a low-cost method and environmentally friendly for bioremediation of heavy metals and management of resource . The need for an efficient and inexpensive method has interested in case of bio-sorption and bio-accumulation processes using microorganisms as profit systems for removing of heavy metal .
Fungal and bacterial strains have been reported to remove high concentrations of heavy metals from polluted environment using biosorption and bioaccumulation techniques . Bioaccumulation is a process which involves two aspects; active metal uptake and passive metal uptake and may be carried out by any living organism with the ability to withstand the toxic effects of a particular metal ion . Additionally, utilization of potential microbial populations in biosorption process to transform or adsorb heavy metals either by live and dead biomass or by their products have produced to for detoxify of heavy metals forms whether in particulates or as soluble form. Negative charged of microbial cell surface as a result of the presence of different functional groups such as hydroxyl, amines, carboxylic and phenolics give microorganisms an ability for binding with different cationic heavy metals .
As above, microbial strains have different mechanisms for reducing the toxicity of heavy metals through its intracellular and extracellular precipitation, binding of elements to cell wall, adsorption on polysaccharides or by export via various transporters . Also, in wide variety of bacterial strains especially in genus “
Pseudomonas aeruginosaas the most potent bacterial strain for tolerating and uptake heavy metals
4.1 Bacterial community and
Bacteria are microorganism play important role in living world. It represents approximately 108 g of the total living world biomass. They used as bio sorbent because their ubiquity, small size, and ability to grow under different conditions such as
4.2 Tolerance and resistance mechanisms by
4.3 Calculation of removal percentage by
In addition, the results of the study show the potential for the isolated
Also, bacterial strains isolated from the drainage of Kakuri characterized and subjected to the salt concentration of various heavy metals and limited its ability to carry heavy metal and recorded minimally inhibitory concentrations (MIC). This demonstrates their ability to tolerate and live in an atmosphere with high metal salts. Eight (8) heavy metals were examined and included; ZnSO4, CdCl2, CoCl2, K2Cr2O7, CuSO4, HgCl2, NiCl2 and PbCl2 .
Furthermore, other study showed that 90.4% of mercury biosorption was observed on combinations of cultures
In a test in which the removal of heavy metals from waste water is an important target, heavy metals biosorption on biomass of
In another study,
In addition, another study was investigated for biosorption of ionic cadmium by
Additionally, it has been found that the adsorption of heavy metals by
4.4 Plasmid mediated heavy metals in
In addition, genes are set for the degradation of environmental pollution, such as heavy metals, toluene, acids, and pesticides, Halogen and this toxic waste. So, plasmids are required for each compound. It is not that one plasmid reduces all toxic compounds from other groups .
In bioremediation of chromium, bacterial strains show chromosome plasmid resistance and reduced enzyme coordination. In molecular engineering, it can now extract stress by improving even under stress conditions . Also, it has been reported that the plasmid resistance gene is determined in pathogenic bacteria of the genus
4.5 Evaluation of resistant genes in
Firstly, metals-microbial interactions might have several environmental implications. Main resistance mechanisms for some heavy metals as (Cu+, Zn+ and Ni2+) were active efflux transporters. Also, in bacterial strains, molecular basis of zinc resistance determined by presence of znt-related genes. In addition, it investigates adaptation of
Subsequently, the ncc, czc, mer and chr genes responsible for heavy metals resistance to different heavy metals as Cr, Zn, Hg and Ni and which the genes have high homology to the chrB, czcD, mer and nccA genes .
Finally, conjugative plasmid (pUM505) isolated from
Heavy metals pollution cause problems and effect on soil, water, plant, animal, human and ecosystem. Heavy metals cause health risks to human lead to cancer. Also, the highest removal percentage of heavy metals from environment is recorded by microorganisms and plants. Microbial community recorded high tolerance and uptake to different heavy metals such as bacteria, fungi and algae.
Finally, I wish to thank my Mother, Brother, sisters, wife, sons (Khalid and Mohammed) and everyone in my family for their continual guidance.
Conflict of interest
The author declares no conflict of interest.
|MIC||minimum inhibitory concentration|