Transversion of cell polarity from bi- to multipolarity is the mechanism determining multiple spore formation in Anaerobacter polyendosporus PS-1^T

Abstract

The number of spores formed in a single cell of Anaerobacter polyendosporus PS-1^T is significantly influenced by the composition of nutrient media. Depending on carbohydrate concentration in synthetic medium, the number of spores may vary from one or two to as many as five to seven. Investigation of spore formation process by fluorescence and electron microscopy revealed that on media with 0.5–1.0% glucose or galactose most of vegetative cells remained rod-shaped after cessation of cell division in the culture. The nucleoids of these cells were localized at cell poles close to the polar site of the cytoplasmic membrane. Fore-spores were formed at one or both of these poles. A satellite nucleoid (operator) was observed close to each forespore. In the variant with bipolar organization of mother cells, only one or two spores per cell were formed. In the second variant of culture development, when the cells were grown at low galactose concentrations (0.1–0.3%), most of vegetative cells increased in volume and became oval or spherical after cessation of cell division in the culture. Epifluorescence microscopy with nucleic acid-specific fluorochromes (DAPI and acridine orange) revealed the presence of multiple (six to nine) nucleoids in these cells. The nucleoids were located at the cell periphery in close contact with the cytoplasmic membrane. These nucleoids became the centers (poles) for forespore formation. Thus, in the early stationary phase transversion from bipolar to multipolar cells occurred. Cessation of cell division combined with continuing replication of the nucleoids resulted in formation on multinuclear cells. The multiplicity of nucleoides and multipolarity of these cells were prerequisites determining endogenous polysporogenesis, occurring as synchronous formation of three to seven twin spores in many of the oval and spherical cells.