Impact of acetate, pyruvate, and physiological state on respiration and respiratory quotients in Pseudomonas nautica

Physiological rates of CO2 production and O-2 consumption, and the activiti es of isocitrate dehydrogenase (IDH) and the electron transfer system (ETS) were studied in the marine bacterium Pseudomonas nautica growing on acetat e. In exponential growth, IDH and ETS activities were well coupled with CO2 production and O-2 consumption rates, but in senescence they were uncouple d. Our results clearly show that under starvation conditions, IDH and ETS a ctivities remained high even though their corresponding respiration rates d ropped. The respiratory metabolism in the different physiological states of the acetate-grown cultures was compared with previous observations made in pyruvate-grown cultures. Time profiles of CO2 production and O-2 consumpti on rates showed completely different respiratory fingerprints associated wi th the different carbon sources. Acetate-grown cultures showed an increase of respiratory quotients (RQ) in the senescence phase whereas in pyruvate-g rown cultures it stayed close to 1.0. On both carbon sources, respiration t o respiratory capacity ratios were constant in exponential phase and decrea sed to almost zero after carbon source exhaustion. Our results clearly show the impact of physiological state and carbon sources on bacterial respirat ion rates.