A Rhodobacter sphaeroides puf L, M and X deletion mutant and its complementation in trans with a 5.3 kb puf operon shuttle fragment

A Rhodobacter sphaeroides puf L, M and X deletion mutant was constructed using interposon mutagenesis. The puf L, M and X genes were replaced with a kanamycin resistance cartridge isolated from the transposon Tn5. The deletion strain PUFLMX 21 did not grow photoheterotrophically and was resistant to kanamycin. Southern blot analysis of genomic DNA from the deletion strain confirmed that the kanamycin resistance was inserted specifically into the puf operon and that the L, M and X genes were deleted. A spontaneous carotenoid mutant of PUFLMX was selected and was found to accumulate primarily neurosporene. Spectroscopic analysis of chromatophores isolated from the deletion strain showed normal B875 and B800-850 expression providing further evidence that the photosynthetic minus phenotype was not the result of insertional inactivation of the promoter region of the puf operon, or the puf Q region. The deletion strain could be returned to the photosynthetic plus phenotype by complementation in trans with a 5.3 kb puf operon shuttle fragment, although the generation time of the complemented strain was 30% longer than wild type.