Some Quantitative Relationships in Bacterial Population Cycles

Abstract

The growth cycles of 4 common saprophytic bacteria (Escherichia coli (2 strains), Aerobacter aerogenes, Serratia marcescens and Chromobacterium violaceum) were determined in nutrient broth at 22, 27, 32, 37 and 42[degree]C. Enumeration of cells was by plate count, using 5 plates of a suitable dilution of pooled, duplicate cultures, counts being made at 2-hr, intervals. The growth curves were sigmoid, but not symmetrical about the point of inflection. The temp, quotient, Q10, of the rate of reproduction varied inversely with temp. With one exception, the maximum rate of reproduction at a given temp, was the same whether the culture used for inoculation was first acclimatized to that temp, or to room temp. (22[degree]C). At any temp, up to the optimum, the ratio of minimum generation time (in minutes) to length of logarithmic phase (in hrs.) at the same temp. was approximately constant (5:1), both for the same organism at different temps. and for different organisms at the same temp.