| Abstract: | An experimental procedure for rapidly obtaining cell populations of Rhodopseudomonas sphaeroides which exhibit reproducible patterns of division and genomic synchrony has been developed. Specifically, the procedure capitalizes upon the cellular metabolic responses displayed by phototrophically growing cells of R. sphaeroides that have been subjected to an immediate decrease in the light intensity employed for growth. Following an abrupt transition of high light (500 ft-c.) adapted, asynchronously dividing cell populations of R. sphaeroides to growth at a low light intensity (50 ft-c.), an immediate cessation of increases in culture turbidity, total cell number and net accumulations of culture DNA and phospholipid occurs. Cellular carotenoids and bacteriochlorophyll continue to be produced, although at a reduced rate. Total cell number remains constant for 2.5 hrs following the transition to growth at low light; at which time, it undergoes a sharp increase (≃38%). This increase in total cell number occurs in the absence of net increases in the accumulation of culture DNA and phospholipid and is accompanied by only a negligible increase in culture turbidity. Reinitiation of high light growth 1 hr subsequent to this increase in total cell number results in a cell population possessing a high degree of division and genomic synchrony. Freeze fracture electron microscopy studies have revealed that this cell division occurs without septation but rather by invagination of preexisting membrane. |
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