Rhizobial exopolysaccharides: A novel biopolymer for Legume-Rhizobia symbiosis and environmental monitoring

Abstract

Extracellular polymeric substances produced by microorganisms are a complex mixture of biopolymers mainly consisting of polysaccharides along with fewer amounts of proteins, nucleic acids, uronic acids, lipids, and humic substances. Biopolymers secreted by microorganisms are considered as a potential alternative over conventional chemical polymers because of their easy biodegradability, nontoxicity, and renewable nature. Exopolysaccharides (EPSs) released by rhizobia play a pivotal role in both establishment of effective symbiosis with leguminous plants and adaptation to environmental stresses. Moreover, low-molecular-weight fraction of this polysaccharide acts as a signal molecule in the symbiotic dialogue. Besides these, EPSs extracted from different microbes have been recognized as a sustainable flocculant for their application in different types of wastewater treatment. EPS has also been considered as a good bioemulsifier for different hydrocarbons. Microbial EPSs have also been found useful in removal of pollutants from contaminated sites. In this chapter, the role of rhizobial EPS in developing effective legume-rhizobia symbiosis is discussed. Also, the role of EPS secreted by root-nodulating bacteria in remediation of heavy metals and hydrocarbon degradation has been highlighted.