Studies of population development in cultures of Escherichia coli
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The bacterial growth curve, or more precisely, the bacterial population curve, ie generally considered to consist of eight distinct phases. These are: (1) the Initial Stationary Phase, in which no multiplication occurs but the cells may enlarge while adjusting to the new environment; (2) the Lag Phase, where reproduction occurs at an increasing rate; (3) the Logarithmic Growth Phase, in which the logarithm of the number of cells increases linearly with time and the generation time is constant and the shortest found in the curve; (4) the Negative Acceleration Phase, in which the reproduction rate slows down and the generation time increases: (5) the Maximum Stationary Phase, where the maximum population is reached and the reproduction rate just balances the death rate; (6) the Accelerated Death Phase, consisting of an increasing death rate; (7) the Logarithmic Death Phase, which is the inverse of the third phase with the cells dying at a maximum and constant rate: and (8) the Decreasing Death Phase, in which a few survivors may be present almost indefinitely. Most of the study of the population curve to date has dealt with the first three phases, in which the bacterial culture is most active both reproductively and physiologically. The present research is concerned primarily with the problems of the Maximum Stationary Phase (MSP). Working with Escherichia coli, Dr. Robert F. Brooks, Department of Botany, University of Missouri, had noted what were apparently fluctuations in the MSP. It was brought to the attention of the writer that perhaps these fluctuations could be correlated in some manner either with the age of the culture per se or with a certain period of elapsed time after the onset of the MSP. The purpose of the investigation here reported was to determine any fluctuation which might exist in the MSP of E. coli and, if any were found, whether this phenomenon could be predicted. Also, in conjunction with the primary goal, different methods of culture aeration which might affect the population curve were compared.
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