An Electron Microscope Study of Sporulation and Protein Crystal Formation in Bacillus cereus var. alesti

SUMMARY: Ultra-thin sectioning techniques showed that spores and crystals were formed together in vegetative B. cereus var. alesti, and that the crystals developed in close proximity to nuclear elements. The exosporium which surrounds the mature spore is not a remnant of the vegetative cell wall, which disintegrates, but arises as a discrete membrane within the cell and does not, at any stage, enclose the crystal. Carbon replicas confirmed what has hitherto been only speculation —namely, that the periodicity seen on the crystal is a true feature of the surface topography. Resolution in two dimensions was occasionally possible and its implications with regard to crystal structure are discussed.