Exosporium and spore coat formation in Bacillus cereus T

Abstract

The exosporium of B. cereus T was first observed as a small lamella in the cytoplasm in proximity to the outer forespore membrane (OFSM) near the middle of the sporangium. Serial sections, various staining methods, and enzyme treatments failed to show any connections between the small lamella and the OFSM. The advancing edge of the exosporium moved toward the polar end of the cell until the spore was completely enveloped. The middle coat was formed between the exosporium and the OFSM from a 3 layered single plate or 'belt', consisting of 2 electron dense layers separated by an electron transparent layer. This 'belt', usually first observed toward the center of the sporangium, developed without changing thickness or appearance over the surface of the forespore. Between the middle coat and the OFSM, a layer of cytoplasm about 50 nm thick was enclosed by the developing coat; this became the inner coat. Electron dense material was deposited on the outer surface of the middle coat to form the outer coat.