Flow microfluorometry study of saccharomyces cerevisiae



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The glucose-limited aerobic growth of the yeast Saccharomyces cerevisiae was studied for both batch and continuous operation. Flow microfluorometry (FMF) was used to measure the protein, RNA, and DMA distributions of the culture. These distributions have been determined at different times during batch culture and at steady state for two dilution rates during continuous cultivation. Populations of S. cerevisiae are heterogeneous, i.e. the cells differ in composition and morphology. Certain subpopulations can be identified, however, with respect to the eucaryotic cell cycle phases or certain morphological types. The composition distribution obtained from FMF is a summation of the contributions from these individual subpopulations. This total distribution was mathematically decomposed by a nonlinear least squares fit to yield information on the yeast subpopulations. Protein and RNA subpopulations have been categorized based on morphology. Four subpopulations were identified: small singles, large singles, budding cells, and doubles and pleomorphic cell types. The four subpopulations based on DNA content which were observed have been related to phases of the cell cycle: first gap (Gl), synthesis (S), second gap and mitosis (G2 + M), and greater than (G2 + M). The overall results agree with literature reports and independent classical analyses, both chemical and microscopic. In addition, the FMF results indicate a good correlation between metabolic events and subpopulation trends. The relationship between protein content and morphology is demonstrated. RNA content is shown to portray a similar morphological relationship in most cases, but there are deviations. The analysis of the subpopulations based on DNA content provides information on the cell cycle in these asynchronous populations. Due to the complexity of microbial growth as evidenced here, it is obvious that more detailed and. descriptive modelling is required. It is proposed that information of the type provided herein by FMF will yield data necessary for such models.