To find whether productivity of bacteriocin is controlled between different species under unusual cultural conditions, we used Rhodobacter capsulatus ATCC 17016 as a producer and Rhodopseudomonas palustris ATCC 17003 as an indicator. Rhodobacter capsulatus was cultured under aerobic conditions in the dark in Lascelles medium containing 0.3% Triton X-100. As a result, bacteriocin productivity increased enormously. The optimal pH range of bacteriocin production was 6~7.8. Through partial purification of bacteriocin, the molecular weight was roughly estimated at 14 kDa. Plasmid had no influence on bacteriocin production by Rhodobacter capsulatus. Our findings indicate that culture conditions affect bacteriocin productivity between more distantly related species, and bacteriocin of Rhodobacter capsulatus is not encoded by a plasmid.