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 producer of aglinate lyase was a Gram negative rod with a G+C content of 63 mol%, 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 showed the presence of a region where the cell membrane sinks into the cytosol. The pit and its neighborhood on cells grown in the presence of alginate were specifically stained with ruthenium red. On the basis of these results, we propose, for the first time, the existence of a direct uptake mechanism for polysaccharides through a mouth-like pit on the bacterial cell surface. This finding may provide a new insight into the transport of macromolecules in microbial cell systems.