Photoautotrophic hydrogen production of Rhodobacter sphaeroides in a microbial electrosynthesis cell.

Conventional photoheterotrophic H production by purple sulfur bacteria requires additional organic substrates as the carbon and energy sources. This study examined the novel photoautotrophic H production of Rhodobacter sphaeroides with concomitant CO uptake in microbial electrosynthesis (MES). Under an applied potential of -0.9 V vs. Ag/AgCl to the cathode, Rhodobacter sphaeroides produced hydrogen with CO as the sole carbon source under illumination. The initial planktonic cells decreased rapidly in suspension, whereas biomass formation on the cathode surface increased gradually during MES operation. The electron and carbon flow under photoautotrophic conditions in MES were estimated. Glutamate, as the nitrogen source, enhanced hydrogen production significantly (328 mL/L/day) compared to NHCl (67 mL/L/day) during seven days of operation. The photoautotrophic condition with 6000 lx presented CO consumption and simultaneous biomass formation on the cathode electrode. MES-driven electron and proton transfer enabled the simultaneous production of hydrogen and CO uptake