Light-activated, -inhibited and -independent denitrification by a denitrifying phototrophic bacterium

Effects of illumination on denitrification by a freshly isolated denitrifying phototrophic bacterium were investigated. Denitrification activity was induced when cells were grown in either light or darkness in the presence of nitrate without oxygen. Denitrification of nitrate with malate as the electron donor by cells at a phase of exponential growth occurred independently of illumination while that by cells in a stationary phase was activated. Effects of illumination on denitrification varied with electron donors. Using malate or succinate, denitrification by cells in a stationary phase was accelerated by illumination, inhibited when glucose or lactate was used, and independent of illumination when pyruvate was used. Denitrification by cells in an exponential phase was independent of illumination when succinate, malate or pyruvate was used and inhibited by it when glucose or lactate was used. Effects of illumination on the denitrification of nitrite were similar to those involving nitrate. Effects of various inhibitors on denitrification were examined in light-succinate and dark-lactate systems. Differences between the two systems are discussed.