Assimilation efficiency and energy contents of prototrophic bacteria

Abstract

AbstractWhen the assimilation efficiency in batch culture of a variety of heterotrophic bacteria was tested in media containing progressively smaller concentrations of carbon substrate, two groups emerged. Those in the first group assimilated carbon progressively more efficiently as the initial concentration in the culture medium was lowered below 2 mg C/ml; some displaying efficiencies exceeding 80%. Those in the second group assimilated carbon at rates that changed little, if at all, with changes in the initial concentrations of carbon substrate. Members of the second group differed from the first in their metabolic versatility as evidenced by the ability of each to catabolize hydrocarbons. The energy content (heat of combustion) of the cells of the species tested varied little with changes in cultured conditions, and values for all fell close to the average for bacteria (5411 cal/g ash‐free dry wt). In continuous aerobic culture on glucose‐minimal medium, the carbon assimilation and energy assimilation efficiencies were simultaneously maximal for Enterobacter aerogenes when the input carbon concentration was 0.2004 mg/ml and the dilution rate was 0.57. An equation for predicting heat of combustion of cells from knowledge of their C,H,N, and O ratios was devised and tested. Precision ranged from +6% to −16%.