Characterization of the H2 production activity in Rhodopseudomonas palustris

Photosynthetic purple bacteria, such as Rhodobacter, Rhodopseudomonas, and Rhodospirillum are among the various types of hydrogen producing microbes that are anoxygenic phototrophs and capable of using light for H2 production. Here we report that Rhodopseudomonas palustris strain HaA2 encodes for a novel hydrogenase (hyq) that can produce H2 under phototrophic conditions. In addition to the hyq operon, R. palustris HaA2 also possesses the known molybdenum dinitrogenase complex (nif), which produces H2 as an obligate byproduct of N2 fixation. Through a series of deletion mutants only the Nif and Hyq enzymes produced H2 in HaA2, under all the conditions tested. Furthermore, H2 production in HaA2 can be driven by succinate oxidation, but not thiosulfate under the conditions tested.