Studies on Cell Arrangement in Bacterial Colonies by Scanning Electron Microscopy

Application of CO₂ Critical-Point Drying Technique

Abstract

Scanning electron microscopy was proved to be useful for observation on the cell arrangement in bacterial colonies. Satisfactory results were obtained by employing such preparative procedures as cultivation on the cellulose dialysis membrane and the CO₂ critical-point drying technique. The double fixation with osmic acid vapor and 3% glutaraldehyde on colonies was also effective, although optimal fixation time varied from one species to another.
Studies were made on several species of the genera Lactobacillus, Bacillus, Corynebacterium, and Salmonella. It was concluded that there was an intimate relationship between the macroscopic appearance of colonies, especially the regular or irregular outer edge and the smooth or rough surface, and scanning electron microscopic findings, such as regular or irregular cell arrangement, and the chain formation and angular apposition of daughter cells after cell division within colonies.