Improved conditions for studying the growth, morphology and ultrastructure of Mycoplasma hominis (ATCC 14027) have been developed. Electron microscopy of whole cells, which had been fixed "in situ", indicated that M. hominis replicated by binary fission during exponential growth. Upon further incubation pleomorphic forms appeared. Four other strains of M. hominis showed similar behaviour. The pleomorphic populations contained cells within the size range of mycoplasma "elementary bodies". These were isolated by sequential filtration using gravity - after pronase treatment had dispersed aggregates. Only a negligible number of the cells passing the membrane of 220 nm pore size were viable, indicating that these were not essential reproductive units but probably involution forms. Examination of thin-sections of cells from logarithmic phase growth revealed structures not heretofore reported: intracellular, spherical, virus-like particles of 31 nm diameter; "septa" formation prior to cell division; and, possibly, on internal network of fibrils.

Gill, P. (Supervisor)