The contribution of iso-high-potential cytochrome c₈ (iso-HPc₈/NirM) to the cyclic electron transport in photosynthesis and sequence characterization of a DNA region around the nirM in Rubrivivax gelatinosus

Abstract

A photoheterotrophic bacterium, Rubrivivax gelatinosus, possesses HiPIP, high-potential (HP), low-potential (LP) cytochrome c₈ and cytochrome c₄ which can work as electron donors to the photosynthetic reaction center. Additionally, we have recently identified an isotype of HP cytochrome c₈ from a mutant strain that spontaneously suppressed previous mutant deficiencies in the photosynthetic capabilities of the four other electron carriers. In this study, we demonstrated that this iso-HP cytochrome c₈ potentially supports cyclic electron transfer during photosynthetic growth. Furthermore, a 10-kb DNA region around the gene for the iso-HP cytochrome c₈ was determined. Within this region we found a gene cluster (nirESMCFDLGHJN) for cytochrome cd₁-type nitrite reductase (Nir). The iso-HP cytochrome c₈ gene is 59% homologous to NirM from Pseudomonas aeruginosa, which donates an electron to Nir. In order to define physiological roles of this cytochrome in Rvi. gelatinosus, the construction of a mutant devoid of iso-HP cytochrome c₈ is in progress.