Storage Polysaccharides in Prokaryotes: Glycogen, Granulose, and Starch-Like Granules

Homopolymers of D-glucose represent the most successful and abundant polysaccharides found in nature. In this chapter, we will focus on α-glucan polysaccharides in particular glycogen and its derivatives (i.e., granulose, starch) that define probably one of the oldest forms of carbon storage among prokaryotes. They are made of linear chains of glucosyl units joined by α-1,4 glycosidic bonds and hooked to each other by α-1,6 glycosidic bonds, referred to as branching points. The glucan chains are organized in such manner that α-glucan polysaccharides appear mostly in the form of tiny hydrosoluble or insoluble water particles in the cytosol of bacteria. Because “Nothing in biology makes sense except in the light of evolution” to quote Dobzhansky, this chapter aims to emphasize the importance of structure-function relationship that determines the physicochemical and biochemical properties of storage polysaccharides in microorganisms.