DIRECT UPTAKE OF ALGINATE MOLECULES THROUGH A PIT ON THE BACTERIAL-CELL SURFACE - A NOVEL MECHANISM FOR THE UPTAKE OF MACROMOLECULES

A yellow-pigmented bacterium isolated from a ditch as a potent produce r of aglinate lyase was a Gram negative rod with a G+C content of 63 m ol%, and was classified in the genus Sphingomonas. Electron microscopy revealed that the bacterial cell surfaces were covered by many large plaits. When grown in a medium containing alginate, a pit of 0.02-0.2 mu m in diameter was formed on the cell surface, and a thin section sh owed the presence of a region where the cell membrane sinks into the c ytosol. The pit and its neighborhood on cells grown in the presence of alginate were specifically stained with ruthenium red. On the basis o f these results, we propose, for the first time, the existence of a di rect uptake mechanism for polysaccharides through a mouth-like pit on the bacterial cell surface. This finding may provide a new insight int o the transport of macromolecules in microbial cell systems.