Characterization and complementation of a mutant of Rhodobacter sphaeroides with a chromosomal deletion in the light-harvesting (LH2) genes.

An LH2- strain of Rhodobacter sphaeroides, DBC1, has been constructed by deleting the puc operon, which encodes the LH2 alpha and beta polypeptides, from the chromosome and replacing it with a kanamycin resistance gene. Southern blot analysis indicates that the 950 bp BamHI restriction fragment which contains the puc operon has been lost and has been replaced by the 1.25 kb Km(R) cassette derived from Tn903. Strain DBC1 lacked the LH2 complex, as shown by loss of the characteristic absorbance bands at 800 and 850 nm. The LH2 polypeptides were also found to be absent after SDS-PAGE. The wild-type phenotype was restored to DBC1 by the transfer of a 3.8 kb BscI fragment containing the puc operon in plasmid pMA81. Transconjugants possessed a wild-type absorbance spectrum and LH2 polypeptides.