Effect of Denitrification on Nitrogen Fixation in Light in a Photodenitrifier, Rhodopseudomonas sphaeroides forma sp. denitrificans

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The effect of denitrification on N_2 fixation was studied in a denitrifying photo-synthetic bacterium, Rhodopseudomonas sphaeroides forma sp. denitrificans. KNO_3 inhibited diazotrophic growth in light, but NO_3^--dependent diazotrophic growth in darkness was found. NO_3^- inhibited C_2H_2 reduction activity in light in cells grown with NO_3^-. NO_3^--dependent C_2H_2 reduction activity in darkness also was present in cells grown with N_2 plus NO_3^-, but not in cells grown on glutamate with NO_3^-. NO_3^- repressed the synthesis of nitrogenase in light. This repression was not overcome by the addition of methionine sulfoximine. The inhibitory and repressive effect of NO_3^- was not mediated by the NO_2^- produced from NO_3^- nor by the NH_4^+ excreted into the medium. But, as N_2 fixation is controlled by O_2 (redox control) it seems to be mediated through the denitrification processes. Much of the glutamine synthetase was adenylylated in cells grown with NO_3^- and its adenylylation state closely parallelled nitrogenase activity in the cells.
日本植物生理学会の論文