Fine Structure of Strictly Anaerobic,Non-Spore-Forming,Gram-Negative Bacilli

The fine structure of a strain of Bacteroides insolitus has been studied by ultrathin sectioning and electron microscopy. Logarithmically growing cells were fixed both by osmic acid and potassium permanganate, and embedded in Epon. Thin sections were stained with uranyl acetate and examined. The periphery of the cell was composed of a wavy three-layered outer membrane (ca. 80 A), an intermediate layer (50–200 A), and three layered cytoplasmic membrane (ca. 80 A). Single or double bridges which connected the outer membrane with the cytoplasmic membrane were observed. Invagination of the cytoplasmic membrane was observed in no occasion. Independent, distinct, and uniform particles were not the main component of the cytoplasm. The cytoplasm was filled with more or less beaded reticulum-like structures. The nucleoplasm with fine fibrils was mainly dispersed continuously in rather regular cubic masses in an intermediate region between the center and the periphery of the cell. Contacts of the nucleoplasm with the cytoplasmic membrane were occasionally observed.