Bioenergetic aspects of aerobic growth of Klebsiella aerogenes NCTC 418 in carbon-limited and carbon-sufficient chemostat culture.

Carbon-limited chemostat cultures of Klebsiella aerogenes NCTC 418 consumed more oxygen per unit of cell synthesis when growing on mannitol or glycerol than when growing on glucose; and since the "maintenance" requirements were similar, this suggested that the extra reducing equivalents present in these compounds were oxidized wastefully. By comparison with carbon-limited cultures, carbon-sufficient cultures that were ammonia-, sulphate- or phosphate-limited generally consumed considerably more oxygen per unit of cell synthesis, particularly at low growth rates. Thus, according to the theory of Pirt, these carbon-sufficient cultures had a greatly increased "maintenance energy" requirement but nevertheless used the remaining energy with a much increased efficiency compared with carbon-limited cultures. This, we suggest, is a false conclusion which stems from the basic assumption that the maintenance requirement does not change with growth rate.