Cell volume distribution patterns were used to characterize the status of physiologically heterogeneous monospecific populations of bacteria. Such physiologically structured populations typically consist of subpopulations of cells in different metabolic and regulatory states. During recovery from starvation the differentiation of active (growing, proliferating) and quiescent (nonproliferating) subpopulations becomes detectable. Since cell volume distributions may be distorted by background noise or debris, we developed a method to extrapolate size distributions from a reduced set of reliable data. The extrapolation procedure is based upon a lognormal distribution of cell sizes. By the same approach we were able to differentiate between subpopulations even when their size ranges overlapped. The analyses of size distributions were also used, partly in combination with fluorescence microscopy, to investigate the population dynamics of Pseudomonas fluorescens and Nitrosomonas europaea during recovery from energy deprivation.Key words: physiologically heterogeneous populations, cell volume distribution, population dynamics, Pseudomonas fluorescens, Nitrosomonas europaea.

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