INFLUENCE OF DILUTION RATE ON NAD(P) AND NAD(P)H CONCENTRATIONS AND RATIOS IN A PSEUDOMONAS SP GROWN IN CONTINUOUS CULTURE

A freshwater Pseudomonas sp. was grown in continuous culture under steady-state conditions in L-lactate-, succinate-, glucose- or ammonium-limited media. Under C limitation, the NAD(H) (i.e., NAD + NADH) concentration of the organisms increased exponentially from approximately 2 to 7 .mu.mol/g dry wt as the culture dilution rate (D) was decreased from 0.5 to 0.02 h-1. Organisms grown at a given D in any of the C-limited media possessed very similar levels of NAD(H). Under these conditions, cellular NAD(H) was only a function of the culture D and was independent of the nature of the culture C source. D had no influence on the NAD(H) content of cells grown under ammonium limitation. Cellular NADH concentration was not influenced by D in C- or ammonium-limited media. In L-lactate-limited medium, bacteria possessed 0.14 .mu.mol NADH/g dry wt: very similar levels were found in organisms grown in the other media. The results are consistent with those of Wimpenny and Firth (1972) that bacteria rigidly maintain a constant NADH level rather than a constant NADH:NAD ratio. NADP(H) (i.e., NADP + NADPH) and NADPH levels were also not influenced by changes in the culture C source or in D; in L-lactate-limited medium these concentrations were 0.07 and 0.53 .mu.mol/g cell dry wt, respectively. The NADPH:NADP(H) ratio was much higher than the NADH:NAD(H) ratio, averaging 55% in C-limited cells.