Cells of Candida utilis were grown under carbon limitation in phased culture at a doubling time of 4 h. The phosphorus contents of four (lipid, cold water extractable, RNA, and DNA) fractions, obtained empirically by serial extraction of the cells, were determined at [Formula: see text]-h intervals during the cell cycle and post-cycle periods. The results showed that the phosphorus composition of the cells was changing throughout both cell cycle and postcycle periods.Each phosphorus fraction doubled during the cell cycle; for the major fractions (cold water extractable P and RNA-P) this occurred as a gradual increase spread over the cell cycle period, but for the minor fractions (lipid-P and DNA-P) the increase was restricted to the latter half of the cell cycle period. Expressed as proportions of the total phosphorus content, the phosphorus contents of the major fractions remained constant, but the minor ones changed during the cell cycle. Other, different, changes were observed between the various fractions during the postcycle period.
Abstract. Changes in phosphorus metabolism were studied by examining the incorporation of a2p and aap into cells of Candida utilis growing in phased culture during a 6 h cell cycle and a post-cycle period of 6 h. Three different chemically defined media were used; these were phosphorus, nitrogen and carbon limited. The patterns of incorporation of phosphorus into RNA, DNA, lipid and cold water extractable phosphate fractions showed a non-uniform behaviour during both cell cycle and post-cycle periods. The patterns were different in all three types of media. The results showed that a cell can grow and develop at a fixed growth rate in different ways: so that the pattern of behaviour during a cell cycle is not stereotyped for a given doubling time, but largely depends upon the nutrient environment in which the cell exists.During the last 25 years an increasing awareness of the fundamental importance of the individual unit--the microbe, rather than the cell population, has developed in relation to the study of microbial growth and metabolism, so that new perspectives are becoming apparent within the discipline of microbiology (Dawson and Phillips, 1974). Nevertheless, our knowledge of such matters is still rudimentary.For a long time, the population in a batch culture has demonstrated the potential range and variability of microbial growth activity by the transient changes occurring within the sequence of its growth curve. Such studies restricted to the overall behaviour of the cell population ignores the microbe as an entity and limits information to the crude level of the mean performance of the cell population that changes as development proceeds in the closed system of culture (Herbert, 1961).With the advent of the open system of continuous flow culture, growth can be stabilised in a condition of equilibrium and, in a chemostat, examined as a steady state at any chosen growth rate.
Incorporation of 33P and 32P into different fractions of continuous phased (synchronized) cultures of Candida utilis was studied. Two different growth conditions (on C-limited and N-limited media) were used at a doubling time of 6 h. Incorporation of 33P and 32P into four fractions (lipid, cold-water ex-tractable, RNA and DNA) showed a variable, nonuniform, behavior during the cell cycle. Different patterns of incorporation between cells on the two media were observed.
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