PLOIDY STUDIES ON THE LARGE CELLS OF MICROCOCCUS AUREUS

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Abstract
The large cells of the apparent life cycle of M. aureus were investigated, and conditions determined under which a large percentage of such cells formed. Cytological studies with various stains and with phase microscopy did not reveal the precise origin of the large cells, but observation suggested an intracellular nuclear fusion to yield a diploid or polyploid nucleus which then underwent meiosis with resulting normal haploid cells. The diploid nature of the large cells was substantiated by radiobiological studies. In these, the dose-survivor relationship was exponential in the normal cells with both X-ray or UV radiations. This single-hit type response can be interpreted as a criterion of haploidy. The dose-survivor curve of the large cells when irradiated by X-ray or UV light was sigmoidal, showing a hit- multiplicity of 2 or more[long dash]thus indicating the diploid or polyploid nature of these cells. Factors of clumping, multi-nuclearity, and "multicellularity" were investigated in order to validate ploidy interpretations of the radiobiological responses. It was found that UV light and certain chemicals would cause an increased incidence of large cells. In many cases the large cells thus produced were indistinguishable from those occurring naturally, but some of the chemicals tested caused atypical large cells to form. The appearance of the large cells was found to be a fairly generalized phenomenon, since they were found in most of the coccus cultures which were tested. Thus the existence of a simple life cycle involving a ploidy change may be common in the bacteria.

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