| 18179591 |
Bueno E, Bedmar EJ, Richardson DJ, Delgado MJ: Role of Bradyrhizobium japonicum cytochrome c550 in nitrite and nitrate respiration. FEMS Microbiol Lett. 2008 Feb;279(2):188-94. Epub 2008 Jan 2.
Bradyrhizobium japonicum cytochrome c (550), encoded by cycA, has been previously suggested to play a role in denitrification, the respiratory reduction of nitrate to dinitrogen. However, the exact role of this cytochrome in the denitrification process is unknown. This study shows that cytochrome c (550) is involved in electron transfer to the copper-containing nitrite reductase of B. japonicum, as revealed by the inability of a cycA mutant strain to consume nitrite and, consequently, to grow under denitrifying conditions with nitrite as the electron acceptor. Mutation of cycA had no apparent effect on methylviologen-dependent nitrite reductase activity. However, succinate-dependent nitrite reduction was largely inhibited, suggesting that c (550) is the in vivo electron donor to copper-containing nitrite reductase. In addition, this study demonstrates that a cytochrome c (550) mutation has a negative effect on expression of the periplasmic nitrate reductase. This phenotype can be rescued by extending the growth period of the cells. A model is proposed whereby a mutation in cycA reduces expression of the cbb (3)-type oxidase, affecting oxygen consumption rate by the cells and consequently preventing maximal expression of the periplasmic nitrate reductase during the first days of the growth period. |
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