An expression vector for purple bacteria based on the puf promoter from Rhodobacter sphaeroides was constructed. The 1.2 kb promoter fragment included the pufQ gene, ORFK, as well as the SD sequence and the start codon from pufB. Translational puf:luc fusion was constructed to analyze transcription from the puf promoter. The luciferase expression was negligible under aerobic light conditions and was stimulated more than 700-fold under anaerobic light conditions. When Rb. sphaeroides (pPluc-2) strain was grown photoheterotrophically in batch culture, the luciferase expression was observed during 7 h. The expression time could be greatly extended using continuous cultivation in a photobioreactor.