Enhancement of hydrogen production by a photosynthetic bacterium mutant with reduced pigment

A novel mutant MTP4 was created from the wild-type strain Rhodobacter sphaeroides RV by UV irradiation for the enhancement of hydrogen production. The amount of light absorbed by MTP4 was lower than that by the wild-type strain at any wavelengths ranging from 350 to 1000 nm. This nature enables the illumination of cells in the deeper parts of a reactor. The contents of bacteriochlorophylls and carotenoids of the chromatophores prepared from MTP4 under the conditions for hydrogen production were reduced to 41 and 49% of those from the wild-type strain RV, respectively. Analysis of the light-harvesting (LH) complexes by SDS-PAGE showed that the amounts of LH1s and reaction centers (RCs) in MTP4 were retained, whereas that of LH2s was much less than that in RV. Although MTP4 had less pigments, its growth rate was equivalent to that of RV over a wide range of light intensities. MTP4 produces hydrogen with a stable manner. Using a plate-type reactor, it produced 50% more hydrogen than RV. A novel method of pigment reduction was found to be effective for the enhancement of hydrogen production per unit reactor.