, Volume 134, Issue 1, pp 80-85

Metabolic and energetic aspects of the growth of Klebsiella aerogenes NCTC 418 on glucose in anaerobic chemostat culture

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Abstract

Klebsiella aerogenes NCTC 418 was cultured anaerobically in chemostat cultures (pH 6.8; 35° C) under carbon, phosphate-, ammonia-, sulphate- and potassium-limited conditions with glucose as the sole carbon- and energy source. The rates of uptake of glucose and excretion of fermentation products were quantitatively determined and carbon, hydrogen- and oxygen balances were constructed with recoveries better than 90%.

It was found that under glucose-limited conditions the utilization of the carbon source was the most efficient. Under these conditions the highest Y GLU was obtained whilst virtually all glucose was fermented to acetate and ethanol and formate plus carbon dioxide. Under all glucose-sufficient conditions a branched fermentation was observed with acetate, ethanol, formate plus carbon dioxide, D-lactate, succinate and 2,3-butanediol as end-products. The lower Y GLU values for these cultures appeared to be a consequence of both a decreased Y ATP and a decreased efficiency of ATP synthesis from the dissimilation of glucose. In contrast to aerobic cultures, significant differences in fermentation patterns were not observed between the various glucose-sufficient cultures.

The fermentation patterns of glucose-sufficient cultures appeared to be influenced by the specific growth rate. For all these cultures a lowering of the dilution rate resulted in a smaller fraction of glucose being fermented to acetate and a greater fraction being fermented to 2,3-butanediol. Relatively much glucose was fermented to D-lactate when the organisms were grown at a low dilution rate under sulphate-limited conditions.

Anaerobic, glucose-limited cultures were found to be able to increase their specific uptake rate of glucose instantaneously when pulsed with glucose. The extra glucose taken up was fermented mainly to D-lactate whilst no increase in the specific production rate of acetate and ethanol occurred. The excreted D-lactate probably was not formed from pyruvate, by the NADH-linked lactate dehydrogenase, but via the methylglyoxal bypass. It is suggested that by invoking this bypass reaction K. aerogenes can metabolically uncouple ATP synthesis from glucose dissimilation, and herein may lie the physiological significance of this reaction sequence.