Rhodobacter sphaeroides KD131 and its mutant strain lacking uptake hydrogenase (Hup(-)) and PHB synthase (Phb(-)) have been studied on H-2 production and cell growth under different Culture conditions. Both strains started producing H-2 from the middle of the logarithmic growth phase and continued until the cell concentration leveled out. The rates of H-2 production were 1.32 and 3.34 ml H-2/mg-dcw for the wild-type and Hup(-)/Phb(-) mutant strain, respectively, at the optimum conditions. Malate and lactate were better carbon sources than starch, sucrose or glycerol. Approximately 60% of acetic acid was degraded in 48 h by the wild-type strain and pH increased to 9.4. However, the Hup(-)/Phb(-) mutant strain did not grow well and degraded only 19% of acetic acid. The pH ranges of 7.0 were the optimum for the cell growth and pH 7.5 for the H-2 production. Both strains grew and produced hydrogen under the irradiance of 12-120W/m(2), but cell growth was inhibited over 400W/m(2). (c) 2004 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.