TEMPERATURE SYNCHRONIZATION OF NUCLEAR AND CELLULAR DIVISION IN BACILLUS MEGATERIUM ,

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Abstract
In actively growing cells of Bacillus megaterium (34[degree]C). the nuclei become highly stainable masses made up of contracted chromosomes and associated with distinct centriole-like granules, as a result of a short exposure to the suboptimal temperature of 10 to 15[degree]C. Practically all observed nuclei appear in this metaphase-like configuration. Reincubation at 34[degree]C results in resumed multiplications, synchronous for all the cells and nuclei as ascertained by viable count and cytological studies. Following a 40-minute lag period, the number of bacteria increases in stepwise fashion, each cycle corresponding to one bacterial generation. Nuclear reduplication precedes cellular division. Sister chromosomes separate within 5 to 15 minutes after transfer to 34[degree]C. The nuclear components become progressively more filamentous. Accumulations of condensed metaphase-like nuclei occur in the short intervals coinciding with the onset of the stationary phase of each cellular duplication cycle. Nuclear division in cells thus phased resembles the mitotic cycle in higher organisms. The most obvious effect of decrease in temperature is on the rate of some chemical or physical reaction causing the final separation of sister chromosomes. The use of dilute, liquid cultures necessitated a process for rapid concentration of the cells. Almost instantaneous filtration on "Millipore" filters was followed by fixation in OsO4 vapors, HC1 hydrolysis, staining with thionin and mounting in a solution of "Abopon".