Unusual morphology of Agromonas oligotrophica and the effect of NaCl and organic nutrient on its fine structure.

Fine structure of an oligotrophic bacterium, Agromonas oligotrophica, was studied by electron microscopic observation of thin-sectioned cells. Cells grown in 0.01% (w/v) each of peptone and meat extract (1/100PM) showed the following three remarkable features: (1) Cytoplasm is divided into several compartments which are surrounded by cytoplasmic membrane. (2) Several electron-dense cores are visible in each cell which are stained by DAPI (4, 6-diamidino-2-phenylindole). (3) The organism divides not by the usual septum formation but by irregular budding and/or elongation and pinching off. The process is independent of the cytoplasmic compartmentalization. Cells grown in 1/100PM supplemented with 0.4% (w/v) NaCl or those grown in medium including 0.1% (w/v) each of peptone and meat extract (1/10PM) are characterized by abnormal morphological features; deformed cell shape, incomplete development of cytoplasmic membrane, incomplete compartmentalization of cytoplasm and the hollow space between the outer layer and cytoplasmic membrane. The abnormal morphological appearance may relate to the halo and organo sensitivities of this organism.