Special cell surface structure, and novel macromolecule transport/depolymerization system of Sphingomonas sp A1

A bacterium isolated from soil as an alginate lyase producer shows characte ristic morphological and taxonomical properties consistent with being class ified in the genus Sphingomonas. The bacterium utilizes high molecular weig ht (HMW)-alginate for growth by depolymerization of the polymer with intrac ellular alginate lyases, which are generated from a common precursor protei n through autoregulated post-translational modifications. Electron microsco pic observations of the cell surface and of thin sections of cells grown on HMW-alginate revealed dynamic changes in both cell surface and membrane st ructures, The most remarkable change is recognized in the formation of mout h-like pits which open and close depending on the presence or absence of HM W-alginate. Enzymatic and genetic analyses of HMW-alginate incorporation pr ocesses confirmed the presence of a pit-dependent and macromolecule-specifi c ABC transporter system in cells of Sphingomonas species A1. This is the f irst description of a bacterium with a pit on the cell surface and a pit-de pendent endocytosic uptake system for macromolecules.