ELECTRON MICROSCOPY OF ULTRA-THIN SECTIONS OF BACTERIA

Abstract

In the course of cytological studies of a few selected species of bacteria by the techniques of ultra-thin sectioning and electron microscopy, some new and si8nificant information has been obtained concerning cellular division in Bacillus cereus. The cytoloqg of bacterial cellular division inYneS--a_ number of structures aiid ev-ts which are beyond the resolution limit of the light microscope. The complexity of these structures and -the psi'bl1e variatiow whfch differences in species, age of culture, and growth conditions may introduce have made it impos-sible to make reliable interpretations by indirect methods. This has led to considerable confuwsion as is apparent from any review of the literature. It is hoped that some of the observations made in the present investigation will remove a little of that confusion and point the way to much greater contributions of the method in the future. MATEIUALS AND METHODS A rough variant of B. cereus, obtained from Dr. F. H. Johnson, was used in this study. The bacteria were grown in brain-heart infusion medium (Difco) in 75 ml broth tubes aerated by means of a Thiberg aerator. Seven hour cultures were transferred to centrifuge tubes and the organisms sedimented by a moderate centri-fugation for three minutes. Most of the superna-tant broth was decanted, and the sedimented bacteria were resuspended in the remainder. To the 1 ml (approximately) suspension of bacteria which resulted, 5 ml of a 2 per cent OsO4 solution with 0.8 per cent NaCl were added. The tube was stoppered and put aside for 16 hours. The fixed bacteria were washed several times with