S142: Non-growing photosynthetic bacteria as biocatalysts for hydrogen gas production

The anoxygenic photosynthetic bacterium Rhodopseudomonas palustris has potential as a biocatalyst for hydrogen gas production using its nitrogenase. Cells induced for nitrogenase and deprived of nitrogen gas catalyze the synthesis of pure hydrogen. We have developed mutants in which nitrogenase is insensitive to inhibition by ammonium, thus allowing the possibility of using agricultural and industrial waste streams as feedstocks for hydrogen production. In addition, we have determined that illuminated cells that are not growing divert a large proportion of available electrons from electron-donating compounds like acetate or thiosufate to generate hydrogen. Energy from light drives this process and such cells do not need to use any of the electron-donating compounds that they are supplied for their own growth. R. palustris can survive in a starved, non-growing state and produce hydrogen gas for periods of months. Transcriptome studies and biomass determinations give some clues as to how cells manage to exist in a state of non-growth for long periods of time.