Bacterial Exopolysaccharides: Insight into Their Role in Plant Abiotic Stress Tolerance

Abstract

Abiotic stresses like drought, salinity, heavy metals, and high or low temperature are major constraints to crop production by being detrimental to the physical, metabolic, and growth development of plants [1]. Plants are often subjected to multiple stresses which are aggravated by climatic changes, use of chemical fertilizers, pesticides and environmental pollution. This situation is more alarming with the increase in world population which is expected to reach around 10 billion by 2050 [2]. There is an urgent need to increase food production by 70% to meet the demand [2]. It is also imperative to find ways to implement new agricultural strategies to protect crops from these multiple abiotic stressors [3].Currently, there are several approaches that enhance plant tolerance to abiotic stress. These include waterconserving irrigation strategies, traditional methods of breeding, and genetic engineering of transgenic plants with abiotic stress tolerance [4]. Plant growth-promoting rhizosphere microorganisms are also now being widely used for restoring soil fertility, remediation of chemical pollutants and to sustain plant growth [5]. They are a proven, effective alternative to conventional methods and a promising strategy for mitigating abiotic stresses. The use of plant growth-promoting microorganisms is a simple alternative approach to genetic engineering and breeding methods for crop improvement since these procedures are time-consuming, expensive, and laborious [6]. These microorganisms improve the root and shoot growth, thus enhancing the water and nutrient absorption from soil [7]. Different types of plant metabolites, such as HCN, 2,4-diacetylphloroglucinol (DAPG) [8], antibiotics, e.g., phenazine [9], and volatile compounds [10] help to enhance plant growth [11][12][13]. Exopolysaccharides, are produced by an array of microorganisms like bacteria, cyanobacteria, microalgae, yeasts, and fungi [14]. These exopolysaccharides impart defense against a wide range of environmental stresses like drought [15], metals [16], salt [17], and temperature [18]. Additionally, EPS facilitate microbe-microbe and microbe-plant interaction, provide antioxidants, store carbon, and supply nutrients to support plant growth [6,19]. Diverse bacterial species like Pseudomonas aeruginosa, Azotobacter vinelandii, Sphingomonas paucimobilis, Azotobacter, Paenibacillus, Klebsiella, Bacillus, and Pseudomonas spp. produce EPS and play an important role in sustaining plant growth in abiotic stress environments [20]. The root microbiome, specifically rhizospheric microbes produce phytohormones, 1-aminociclopropane-1-carboxylase (ACC) deaminase, and EPS to sustain Various abiotic stressors like drought, salinity, temperature, and heavy metals are major environmental stresses that affect agricultural productivity and crop yields all over the world. Continuous changes in climatic conditions put selective pressure on the microbial ecosystem to produce exopolysaccharides. Apart from soil aggregation, exopolysaccharide (EPS) production also helps i...

Mycobacterial Adhesion: From Hydrophobic to Receptor-Ligand Interactions

“…Although some of these lipids were also reported to be constituents of the biofilm extracellular matrix, it has been proposed that their major participation in biofilm formation is more likely to be in direct interbacterial adhesion and involves their hydrophobicity (at least in the case of the less amphiphilic ones) [59]. While exopolysaccharides are abundant in the extracellular matrices of many microbes [60][61][62][63][64], evidence of these complex carbohydrates in mycobacterial biofilms have been lacking. Very recently, a rapidly inducible surface-attached in vitro biofilm model was devised for M. tuberculosis [47,65].…”

Microbial Derived Compounds Are a Promising Approach to Mitigating Salinity Stress in Agricultural Crops

“…Microbial exopolysaccharides are diverse, varying in function and structure and differ across microbial species. The concentration of EPS produced also differs across species (Bhagat et al, 2021). Their structure is complex, comprising biomolecules such polysaccharides, structural proteins, enzymes, amino sugars, nucleic acids, lipids, pyruvates, glycoproteins, etc.…”

“…(Mishra and Jha, 2013). PGPM produce exopolysaccharides for reasons such as, aiding microbial attachment to plant roots and formation of biofilms (Ruppel et al, 2013;Qin et al, 2016;Liu et al, 2017b;Bhagat et al, 2021). EPS bind with cations, such as Na + , lowering their bioavailable ions and hence, plant uptake, creating osmotic balance and stabilizing the soil ionic balance, thus, mitigating osmotic and oxidative stress in plants (Kumar et al, 2020;Lopes et al, 2021).…”

The Regulatory Functions of σ54 Factor in Phytopathogenic Bacteria

“…They contain organic macromolecules, such as polysaccharides, proteins, and phospholipids in addition to some non-polymeric molecules [ 119 , 120 ]. They are microbial biopolymers produced under stress in harsh environments and nutrition-deprived conditions [ 121 ]. Therefore, EPS production is one of the strategies of bacteria to fight against biotic and abiotic stresses.…”