Comparison of H2H2 accumulation by Rhodobacter sphaeroides KD131 and its uptake hydrogenase and PHB synthase deficient mutant

Rhodobacter sphaeroides   KD131 and its mutant strain lacking uptake hydrogenase (Hup--) and PHB synthase (Phb--) have been studied on H22 production and cell growth under different culture conditions. Both strains started producing H22 from the middle of the logarithmic growth phase and continued until the cell concentration leveled out. The rates of H22 production were 1.32 and 3.34 ml H22/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 H22 production. Both strains grew and produced hydrogen under the irradiance of 12–120 W/m22, but cell growth was inhibited over 400 W/m22.