The effect of the respiratory electron acceptor nitrous oxide on the synthesis of the photosynthetic apparatus of was examined. In phototrophically grown cells, the addition of nitrous oxide caused a reduction in the level of light-harvesting complex I and light-harvesting complex II under conditions of high light intensity (200 W m) and low light intensity (16 W m). 5-Aminolaevulinate synthase activity was decreased during growth in the presence of nitrous oxide and this limited production of spectral complexes since addition of exogenous 5-aminolaevulinic acid partially suppressed the effect of nitrous oxide. The effect of nitrous oxide on the expression of the operons encoding the pigment-binding proteins of light-harvesting complex I (), light-harvesting complex II () and the two isoenzymes of 5-aminolaevulinate synthase ( and ) were measured using transcriptional fusions to Nitrous oxide caused a decrease in and transcription. However, there was an apparent increase in the expression of and transcriptional fusions. The level of light-harvesting complexes in cells grown in the dark with different electron acceptors was also examined. Cells grown anaerobically with DMSO had a higher level of light-harvesting complexes than those grown anaerobically with nitrous oxide as electron acceptor. Cells grown aerobically had the lowest level of light-harvesting complexes. It is proposed that FnrL-dependent and FnrL-independent expression of photosynthesis genes is modulated by redox changes elicited by nitrous oxide respiration.


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