[Electron microscopy of the surfaces of bacillary spores]

The surface structures of the spores of Bacillus. cereus, B. thuringiensis, and Brevibacillus laterosporus were studied by transmission and scanning electron microscopy. Platinum deposition and negative staining with uranyl acetate revealed appendages and exosporium in B. thuringiensis and B. cereus. The exosporium structure was visualized by negative staining and ultrathin sectioning. For staining the exosporium polysaccharide, Alcian blue was used during fixation. The results obtained show the differences in structural organization of appendages and exosporium in different strains. Canoe-shaped inclusions were revealed in all Br. laterosporus strains, while strain IGM16-92 had a fibrillar capsule as well. Electron microscopy using a dual beam scanning electron microscope Quanta 200 3D provided the information of the spore surface relief without sample treatment (fixation and dehydration). The spores of Br. laterosporus strains had folded surface, unlike the smooth surface of B. cereus and B. thuringiensis spores. Diversity of external spore structures was shown within a species, which may be used for detection of bacteria at the strain level. Optimized procedures for visualization of spore surface by different electron microscopic techniques were discussed.