Variations in enzyme activities of Butyrivibrio fibrisolvens and Ruminococcus albus grown in continuous culture

One strain each of Butyrivibrio fibrisolvens and of Ruminococcus albus were grown in continuous culture under glucose limitation at three dilution rates. The activities of several intermediary enzymes were determined in cell-free extracts. In both organisms, the coefficients of variation of enzyme activities were, with few exceptions, much larger than those of the dry-weight concentration of cells and of glucose uptake from the medium. In B. fibrisolvens, the coefficients of variation of all enzyme activities per milliliter of culture were much greater at a dilution rate (D) of 0.5 h−1 than at D = 0.12 and 0.2 h−1. In R. albus, on the other hand, the coefficients of variation were greater at D = 0.1 h−1 than at D = 0.2 and 0.43 h−1. Cell counts made at short intervals over a period covering three doubling times of a R. albus culture growing under steady-state conditions provided no evidence of synchrony of cell divisions that might account for the fluctuations in enzyme activities. The results indicate the importance of determining the extent of variations in enzyme activities in cells growing at a particular growth rate under steady-state conditions before attempting to compare the effect of different growth rates on enzyme activities. The implications of these findings are discussed in relation to an earlier study on changes in enzyme activities in extracts of the mixed microbial population of an experimental anaerobic digester during adaptation to a synthetic substrate and after prolonged operation on this substrate.