Characterisation of a Rhodobacter sphaeroides gene that encodes a product resembling Escherichia coli cytochrome b(561) and R-sphaeroides cytochrome b(562)

Analysis of the photoactive yellow protein (pyp) gene region of Rhodobacter sphaeroides has revealed the presence of an additional open reading frame, orfD, that had not previously been identified. Here we report the location of this new gene and the predicted amino acid sequence of the encoded prot ein. The translation product resembles a group of small cytochrome b-like p roteins, including Escherichia coli cytochrome b(561), R. sphareroides cyto chrome b(562), and two new cytochrome b(561)-like proteins identified using the E. coli genome sequence, for which functions have not yet been establi shed. To determine OrfD function in R. sphaeroides, an orfD mutant was cons tructed. The OrfD mutant exhibited growth rates and yields very similar to those of the wild-type strain when grown under a variety of growth conditio ns. Respiration rates, reduced-minus-oxidised spectra and levels of photosy nthetic complexes were also very similar in the two strains. Although the r ole of OrfD was therefore not determined here, we demonstrate that the orfD gene is expressed in R. sphaeroides under aerobic, semi-aerobic and photos ynthetic growth conditions. (C) 2000 Published by Elsevier Science B.V. on behalf of the Federation of European Microbiological Societies.