H 2 photoproduction by batch culture of Anabaena variabilis ATCC 29413 and its mutant PK84 in a photobioreactor

Hydrogen production by Anabaena variabilis ATCC 29413 and of its mutant PK84, grown in batch cultures, was studied in a photobioreactor. The highest volumetric H 2 production rates of native and mutant strains were found in cultures grown at gradually increased irradiation. The native strain evolved H 2 only under an argon atmosphere with the actual rate as high as the potential rate (measured in small vials under optimal conditions). In this case 61% of oxygenic photosynthesis was used for H 2 production. In contrast the mutant PK84 produced H 2 during growth under CO 2 ‐enriched air. Under these conditions at the maximum rate of H 2 production (10 mL h −1 L −1 ), 13% of oxygenic photosynthesis was used for H 2 production and the actual H 2 production was only 33% of the potential. Under an atmosphere of 98% argon + 2% CO 2 actual H 2 production by mutant PK84 was 85% of the potential rate and 66% of oxygenic photosynthesis was used for H 2 production. Hydrogen production under argon + CO 2 by the mutant was strictly light‐dependent with saturation at about 300 μE m −2 s −1 . However, the rate of photosynthesis was not saturated at this irradiation. At limiting light intensities (below 250 μE m −2 s −1 ) 33–58% of photosynthesis was used for H 2 production. Hydrogen evolution by PK84 under air + 2% CO 2 was also stimulated by light; but was not saturated at 332 μE m −2 s −1 and did not cease completely in darkness. The rate of oxygen photoevolution was also not saturated. A mechanism for increasing cyanobacterial hydrogen production is proposed. © 1999 John Wiley & Sons, Inc. Biotechnol Bioeng 64: 709–715, 1999.