Summary: Growth of 12 strains in a broth medium with and without aeration was compared. In general, the aerated cultures grew faster and produced more biomass, at the expense of glucose and other sugars, than unaerated cultures. The more efficient growth correlated well with the production of acetate rather than ethanol as an end-product of metabolism in aerated cultures; unaerated cultures produced little or no acetate.

Mutants of X2 were isolated that had lost the capacity to be stimulated by aeration; they were completely deficient in NAD(P)H oxidase activity and did not accumulate acetate in aerobic cultures. Without NAD(P)H oxidase the mutants rely on the ethanol branch of the heterolactate pathway to regenerate NAD(P) from NAD(P)H, irrespective of the presence or absence of O. The presence of NAD(P)H oxidase in parental cultures allows them to utilize O as a terminal electron acceptor and produce more ATP per mol of sugar utilized when O is available than when it is limiting.


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