[Submicroscopic organization and spore formation of Desulfotomaculum nigrificans]

Abstract

The submicroscopic organization and spore formation were studied in two strains of Desulfotomaculum nigrificans, 435 and 781. Cross-sections of cells fixed with osmic acid and contrasted with uranyl acetate and lead citrate revealed a cell wall devoid of the outer lipoprotein membrane, which was typical of gram-positive bacteria. The cell wall consisted of three electron-dense layers and two layers of lower electron density. A layer of a microcapsule having fibrillar structure and a thickness of 23-33 nm was detected on the surface of the cell wall. The cytoplasmic membrane and intracellular membrane structures were represented by the Robertson membrane about 9 nm thick. The cytoplasm contained electron-dense polyribosomal granules and inclusions having fine-granular structure. The nucleoid was located in the central part of the cell as an electron-transparent zone penetrated with electron-dense DNA threads 2.5 nm thick. The paper presents microphotographs of the main stages of spore formation which follows the mechanism described for bacteria of the Bacillus genus. The poles of spindle-like cells have electron-dense disk-shaped formations covered with a three-layer membrane and containing electron-dense granules, apparently, corresponding to polyribosomes.