Microbial Exopolysaccharides
Microbial polysaccharides are produced in two forms, capsular polysaccharide (CPS) and exopolysaccharide (EPS). EPSs of microbial origin are ubiquitous in nature, have unique properties, and can be isolated from the bacteria in fresh water, marine environ
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Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179 Sources of Exopolymers Producing Bacteria . . . . . . . . . . . . . . 180 Biosynthesis and Genetic Regulation . . . . . . . . . . . . . . . . . . . . . . 181 EPS Composition and Analytical Techniques/Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182 Common Exopolysaccharides: Property and Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187 Future Prospects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189
Abstract Microbial polysaccharides are produced in two forms, capsular polysaccharide (CPS) and exopolysaccharide (EPS). EPSs of microbial origin are ubiquitous in nature, have unique properties, and can be isolated from the bacteria in fresh water, marine environment, extreme conditions, and soil ecosystem. Exopolysaccharides are comprised of repeated units of sugar moieties, attached to a carrier lipid, and can be associated with proteins, lipids, organic and inorganic compounds, metal ions, and DNA. Specific functions and precise role of EPSs depend on structural units and ecological niches of the host microorganisms. EPSs produced by bacteria have great potential, and physicochemical characteristics of EPS decide its possible commercial application ranging from pharmaceutical to foodprocessing, extended to detoxification, bioremediation, paints, biotechnology, and petrochemicals. Exploitation of microbial exopolysaccharides is relatively unexplored and research interest is constantly increasing toward isolation, characterization, and applications of novel exopolysaccharides as renewable resources. Downstream processing and genetic engineering for enhanced biosynthesis of EPS require further emphasis.
Introduction Extracellular polymeric substances are metabolic products. Their production by selected microorganisms was first reported in the 1880s (Whitfield 1988). Extracellular polysaccharides (EPSs) accumulate on the microbial cell surface and provide protection to the cells by stabilizing membrane structure against the harsh external environment. EPSs also serve as carbon and energy reserves. EPSs are a heterogeneous matrix of polymers
comprised of polysaccharides, proteins, nucleic acids, and (phospho) lipids (McSwain et al. 2005). Generally, EPSs have often been reported in bacteria and cyanobacteria (De Philippis et al. 2001; Parikh and Madamwar 2006; Chi et al. 2007); however, they have also been reported in the marine microalga Chroomonas sp. (Bermu´dez et al. 2004), Dunaliella salina (Mishra and Jha 2009), the medicinal mushroom Phellinus linteus (Zou et al. 2006), yeast (Duan et al. 2008), basidiomycetes (Manzoni and Rollini 2001; Chi and Zhao 2003), and marine microorganisms (Satpute et al. 2010). EPS-producing microorganisms have been isolated from different natural sources of both aquatic and terrestrial environments, like freshwater, marine water, wastewater,
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