Oxidation-reduction processes in cultures of bacteria II. Anaerobic growth of Bact. lactis aerogenes

Abstract

A survey is made of the carbon sources which will support anaerobic growth of Bact. lactis aerogenes . In all cases where it occurs this is slower than aerobic growth, and entails a greater consumption of the substrate (Pasteur effect). A special study has been made of the phenomena attending the transition from aerobic to anaerobic growth and vice versa. The former transition is accompanied by marked discontinuities. During arrested multiplication there is an enhancement of reducing power, which returns approximately to the original (aerobic) value if anaerobic growth supervenes. In glucose cultures the production of acid now increases several times. The adjustments which these effects indicate require the presence of a nitrogen source for their completion. On the other hand, little adjustment is required for the reverse transition, and the cells apparently retain unimpaired the ability to consume molecular oxygen at the optimum rate as soon as it is again offered. The fermentative production of acid is immediately cut by aeration, even in the absence of any nitrogen source. The various detailed observations are interpreted in the light of the hypothesis that the major adjustment in the transition to anaerobic conditions is the development of a new mechanism for the re-oxidation of reduced hydrogen carriers previously dealt with by the molecular oxygen system. This new process involves extra wasteful consumption of substrate. Its development requires enzymatic adjustments. On the other hand, re-aeration cuts down the fermentative processes by simple lowering of the concentrations of the reduced hydrogen carriers involved.