Need for Cytochrome bc₁ Complex for Dissimilatory Nitrite Reduction of Pseudomonas aeruginosa

Abstract

Pseudomonas aeruginosa strains deficient in the genes for cytochrome c ₁, a subunit of the cytochrome bc ₁ complex, or the tetraheme membrane protein NapC, which is similar to NirT of Pseudomonas stutzeri, were constructed and their growth was investigated. The cytochrome c ₁ mutant could not grow under anaerobic conditions with nitrite as an electron acceptor and did not reduce nitrite in spite of its producing active nitrite reductase. NirM (cytochrome c ₅₅₁) and azurin, which are the direct electron donors for nitrite reductase, were reduced by succinate in the presence of the membrane fraction from the wild-type strain as a mediator but not in the presence of that from the cytochrome c ₁ mutant. These results indicated that cytochrome bc ₁ complex was necessary for electron transfer from the membrane quinone pool to nitrite reductase. The NapC mutant grew anaerobically at the expense of nitrite, indicating that NapC was not necessary for nitrite reduction.

• Pseudomonas aeruginosa
• electron transport
• cytochrome bc ₁
• cytochrome c ₅₅₁
• azurin