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

Abstract

A bacterium isolated from soil as an alginate lyase producer shows characteristic morphological and taxonomical properties consistent with being classified in the genus Sphingomonas. The bacterium utilizes high molecular weight (HMW)-alginate for growth by depolymerization of the polymer with intracellular alginate lyases, which are generated from a common precursor protein through autoregulated post-translational modifications. Electron microscopic observations of the cell surface and of thin sections of cells grown on HMW-alginate revealed dynamic changes in both cell surface and membrane structures. The most remarkable change is recognized in the formation of mouthlike pits which open and close depending on the presence or absence of HMW-alginate. Enzymatic and genetic analyses of HMW-alginate incorporation processes confirmed the presence of a pit-dependent and macromoleculespecific ABC transporter system in cells of Sphingomonas species A1. This is the first description of a bacterium with a pit on the cell surface and a pit-dependent endocytosic uptake system for macromolecules.