Structural studies on bacterial system used in the recognition and uptake of the macromolecule alginate

Alginate is an acidic heteropolysaccharide produced by brown seaweed and certain kinds of bacteria. The cells of Sphingomonas sp. strain A1, a gram-negative bacterium, have several alginate-degrading enzymes in their cytoplasm and efficiently utilize this polymer for their growth. Sphingomonas sp. strain A1 cells can directly incorporate alginate into their cytoplasm through a transport system consisting of a "pit" on their cell surface, substrate-binding proteins in their periplasm, and an ATP-binding cassette transporter in their inner membrane. This review deals with the structural and functional aspects of bacterial systems necessary for the recognition and uptake of alginate. An overall picture of alginate import and depolymerization systems of Sphingomonas sp. strain A1.