Respiration and respiratory enzyme activity in aerobic and anaerobic cultures of the marine denitrifying bacterium, Pseudomonas perfectomarinus

Abstract

Oxygen consumption, nitrate reduction, respiratory electron transport activity, and nitrate reductase activity were measured in aerobic and anaerobic cultures of the marine bacterium, Pseudomonas perfectomarinus. The respiratory electron transport activity was closely correlated with oxygen consumption (r = 0.98) in aerobic cultures and nearly as well correlated with nitrate reductase activity (r = 0.91) and nitrate reduction (r = 0.85) in anaerobic cultures. It was also well correlated with biomass in both aerobic (r = 0.99) and anaerobic (r = 0.94) cultures supporting the use of tetrazolium reduction as an index of living biomass. Time courses of nitrate and nitrate in the anaerobic cultures demonstrated that at nitrate concentrations above 1 mM, denitrification proceeds stepwise. Time courses of pH in anaerobic cultures revealed a rise from 7 to 8.5 during nitrite reduction indicating net proton utilization. This proton utilization is predicted by the stoichiometry of denitrification. Although the experiments were not under ‘simulated in situ’ conditions, the results are relevant to studies of denitrification, to bacterial ATP production, and to the respiratory activity of marine plankton in the ocean.