β-carotene production in a novel hydrogen-producing marine photosynthetic bacterium Rhodovulum sulfidophilum expressing the Erythrobacter longus OCh101 crt I and crt Y genes

Gene transfer in a novel hydrogen-producing marine photosynthetic bacterium, Rhodovulum sulfidophilum, was investigated using the conjugal vector pSUP1021 (Tn5::Km). Kanamycin-resistance transconjugants were obtained at an efficiency of 2.4 × 10^-4 at a mating ratio of 1:10 (E. coli-Rv. sulfidophilum), and the insertion of Tn5 into the chromosomal DNA was confirmed by Southern hybridization. To further establish the gene transfer system in this strain, cloning and expression of the Erythrobacter longus OCh101 crt I and crt Y genes were carried out. The plasmid pRKY415, which carries the E. longus OCh101 crt I and crt Y genes, was stably maintained in Rv. sulfidophilum without significant structural modifications, and the expression of the crt I and crt Y genes altered the original carotenoid biosynthetic pathway of this strain, resulting in the production of β-carotene (20 μg/g dry cells).