Enhanced hydrogen production by a mutant of Rhodobacter sphaeroides having an altered light-harvesting system

A stable mutant of the photosynthetic bacterium Rhodobacter sphaeroides with an altered light-harvesting (LH) system (P3 mutant) was obtained by UV irradiation and characterized. The mutant exhibited a 2.7-fold decrease in the core antennal (LH1) content and 1.6-fold increase in peripheral antennal (LH2) content compared to the wild-type strain. The H2 evolution rates in the P3 mutant under 800- and 850-nm light, corresponding to the absorption maxima of LH2, were 1.5 times higher than in the wild-type strain. The wild-type absorption spectrum was restored in the P3 mutant when a 1.1-kb PCR-amplified fragment containing the puf promoter and pufQBA genes was ligated into a pRK-415 derivative and introduced into it. The transformant showed lower H2 production rates at 800 and 850 nm than the P3 strain carrying the control plasmid, indicating that the accelerated H2 production in the P3 mutant was a result of alterations in the LH system.