Abstract
With the advancements in agriculture, farming community less or more started to rely on synthetic chemicals to increase the crop production and protection. But the negative impact of these chemicals on environment and cropping system urges the scientists to discover some new ways to combat with crop disease. By keeping in view, garlic is a well-known economically important vegetable throughout the world and recognized as reservoir for a number of bioactive compounds to treat various diseases; scientists have developed a strategy to identify and isolate antimicrobial genes from garlic. By using B. subtilis expression systems, a total of 48 antimicrobial genes, including AsR 416, were identified with the potential to significantly retard the growth of economically important fungal and bacterial pathogens. Furthermore, these antimicrobial genes exhibited the thermal stability along with nontoxic effects on mammalian blood cells, which indicate its potential use in the development of human medicines. These genes can revolutionize the way to treat with pathogens and also give a new wave of knowledge to explore the other organisms for the search of antimicrobial genes. This will also help to search the other cost-effective ways for the treatment of plant and human diseases.
Keywords
- Allium sativum L.
- antimicrobial peptide
- Bacillus subtilis
- resistance gene
1. Introduction
Garlic (
During the past few decades, antimicrobial resistance has become one of the most serious and challenging threat for the prevention and treatment of the infectious diseases [9, 10]. Nowadays, much of the attention has been paid to search some new and natural therapeutic agents, which can be used to treat human diseases with high efficacy and minimum adverse effects [11, 12]. Recent advances in research have revealed that there are several natural products with the potential to eliminate or alleviate several serious human diseases, especially cardiovascular, neurodegeneration, cancer, and several other important diseases [13, 14, 15]. A large number of researches have elaborated several herbs with the ability to produce antimicrobial compounds as their defense response against the number of different stresses including microbes [16, 17].
With the advancements in agriculture, farming community started to rely more on synthetic chemicals, which have been considered as an important source for crop production and protection. But, hazardous effects of these synthetic chemicals to environment and cropping system make their use questionable [18, 19]. Besides, pathogens also tended to increase their resistance against these synthetic chemicals and threaten the agriculture sustainability [20, 21]. By keeping these challenges in view, the need of identifying new strategies as an alternative source is increasing interestingly. Recently, scientists are trying to understand the chemistry of secondary metabolites from plants, as studies have revealed these secondary metabolites important in several ways, especially allelopathy, biological control, and biofertilizers, and also some compounds have been identified as biostimulants [22, 23, 24]. Consequently, understanding the mechanism of these secondary metabolites/bioactive compounds from plants can be useful for agricultural community.
2. Antimicrobial potential of Allium species
A number of
2.1 Antibacterial potential
Extracts from the garlic are reported to exhibit the effective results against saprobic and pathogenic bacteria, which are resistant to various drugs [29]. Garlic along with ciprofloxacin exhibits the pronounced inhibition of
Studies have reported that oils and sulfides from elephant (
2.2 Antifungal potential
It is reported in different studies that oils and sulfides from the
Another study has also reported that sterilized/autoclaved garlic and its active compounds exhibit significant antifungal activities than that of antibacterial. Further analysis of garlic antimicrobial products revealed that these products are the heterocyclic sulfides [38], allyl alcohol [39], and 3-(allyltrisulfanyl)-2-aminopropanoic acid [40]. For bacteria and yeasts, minimum inhibitory concentrations (MICs) of heterocyclic sulfides are more than 100 and 1–6 ppm [38], respectively, while for the allyl alcohol, 4% and 55–140 ppm MICs are recorded for bacteria and yeasts [39], respectively. In the case of 3-(allyltrisulfanyl)-2-aminopropanoic acid, 100 ppm and less than 50 ppm MICs are observed for bacteria and yeasts [40], respectively. In previous studies, it was mistakenly stated that autoclaved garlic exhibit less antimicrobial activities than fresh garlic. For this statement, the only reason was that they tested autoclaved garlic against bacteria, which was already very less sensitive than yeasts against garlic [41]. Recent studies have explored the germicidal potential of sterilized/autoclaved garlic.
2.3 Antiviral activity
Diallyl polysulfides, as transformation product of allicin, and ajoene exhibit the antiviral activities. From all the reported
2.4 Antiparasitic potential
A number of parasites, including
From the above discussed literature, it is clear that garlic has a certain pool of antimicrobial genes which can be isolated and studied further to explore their mechanisms. It will provide some new directions for antimicrobial research. Now we will discuss some techniques to isolate and study the antimicrobial genes from garlic.
3. Systems for the isolation of antimicrobial genes from garlic
3.1 Bacillus subtilis and Escherichia coli expression systems
An experiment was designed to study the antimicrobial genes from the garlic. For this purpose, cDNA libraries from garlic were constructed by using two different vectors, pBE-s and pET22 (b), and then transformed into expression systems,
For the screening of libraries, it was considered that because of the toxicity of protein products of cDNA libraries,
3.2 Antimicrobial potential of genes from A. sativum
Antimicrobial potential of
Genes | |||
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+ | |||
+ | |||
+ | |||
Table 1.
Antimicrobial potential of
Gram-negative bacteria | ||||
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Genes | ||||
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+ | ||||
+ | ||||
+ | ||||
+ | ||||
+ | ||||
+ | ||||
+ | ||||
+ | ||||
+ | ||||
+ | ||||
+ |
Table 2.
Antimicrobial potential of
Gram-positive bacteria | |||||||
---|---|---|---|---|---|---|---|
Genes | |||||||
+ | + | + | |||||
+ | + | + | + | + | + | + | |
+ | + | + | + | + | + | + | |
+ | + | + | + | + | + | + | |
+ | + | + | + | + | + | + | |
+ | + | + | + | + | + | + | |
+ | + | + | + | + | + | ||
+ | + | + | + | + | + | ||
+ | + | + | + | + | + | + | |
+ | + | + | + | + | + | + | |
+ | + | + | + | + | + | ||
+ | + | + | + | + | + | + |
Table 3.
Antimicrobial potential of
3.3 Action mechanism of antimicrobial proteins
A study was designed to explore the action mechanism of antimicrobial peptides. In this study,
3.4 Thermal stability and safety analysis of antimicrobial proteins
Proteins from
4. Conclusion
It is an adverse need of modern agriculture to search cost-effective ways to treat the crop diseases, as the potential use of synthetic chemicals also increases the resistance in pathogens. Garlic is a famous vegetable for its potential to treat various kinds of diseases. So, it is obvious that antimicrobial genes from garlic are the best source to incorporate resistance in plants without affecting the other environmental factors. This way of introducing resistance can also help to understand the mechanisms of plant biology to further explore the new strategies.
Acknowledgments
This work was supported by the National Major Project for Transgenic Organism Breeding (2011ZX08003-001 and 2016ZX08003-001) and the Hubei Provincial Technology Innovation Program (2016ABA093).