SPORE STRUCTURE AS REVEALED BY THIN SECTIONS

Abstract

Sections, 0.3 _ 0.4 [mu] thick, of resting spores of Bacillus cereus and B. megaterium were examined in the light microscope after Giemsa staining. Unstained sections were studied in an electron microscope. In B. megaterium spores, a thin, poorly stainable cortex, transparent in electron-micrographs, occurs immediately beneath the spore coat. It cannot be detected with certainty in B. cereus spores. The core of the spores of both spp. consists of basiphil matter which is remarkably dense and homogeneous in electron-micrographs. After extraction of most of the basiphil matter by hydrolysis with [image]/HCl at 60[degree], or treatment with [image]/1 HClO4 or digestion with ribonuclease (the method of choice) a crescent or ring of nuclear elements can be stained at the surface of, but within, the core. The arrangement of the nuclear matter in resting spores is similar to the nuclear ring configurations which ordinary methods have revealed previously in whole spores fixed early during germination. No evidence has been obtained for an extra-cytoplasmic nucleus whose existence in resting spores had been postulated by the writer. Electron-micrographs of B. megaterium spores sectioned after treatment with [image]/1 HNO3 reveal an outward flow of the nuclear material through a gap in the cortex and the inner sporecoat. The eccentric and protruding nuclei which Feulgen-hydrolysis and similar procedures invariably reveal in whole spores, must now be regarded as unavoidable artefacts, characteristic of the resting stage. Observations by Dr. P. C. Fitz-James on spores cracked open by shaking them with minute glass beads give very similar results.