Bacterial degradation of algal polysaccharides in marine ecosystem

Abstract

Complex polysaccharides (CPs) such as agar, alginates, carrageenan, etc., are largely present as component of cell wall of seaweeds, promoting structural integrity and shielding the host from pathogens or predators. Marine bacteria-degrading CPs are ubiquitous and have been isolated from diverse sources such as costal water, sediments, and deep sea, as well as from the surface of seaweeds and crustaceans. Polysaccharide-degrading enzymes (carbohydrases) such as agarase, alginate lyase, and carrageenase are produced by CP-degrading bacteria that aid in depolymerizing agar, alginate, and carrageenan, respectively. The resultant oligosaccharides are subsequently degraded to various intermediates that are further channelized to energy conversion pathways. Several of these carbohydrases have been purified, and study of their biochemical properties such as molecular weight, substrate specificity, pH, and temperature range for optimal activity indicates a vast diversity. Recently, several multiple CP-degrading bacteria (epiphytic/free form) have been isolated. Saccharophagus degradans and Microbulbifer species are the dominant groups of multiple polysaccharide-degrading bacteria and play a significant role in recycling of carbon from CPs. In natural marine ecosystem, the cell wall of seaweeds comprises an array of CPs in mixed proportion. The production of diverse carbohydrases by CP-degrading bacteria enables it to decompose seaweeds into single cell detritus as well as generate reducing sugars from degraded polysaccharides. Thus, CP-degrading bacteria are potential candidates for eco-friendly degradation of algal waste.