Photoproduction of molecular hydrogen by an Anabaena variabilis PK84 culture

Photoproduction of molecular hydrogen by the mutant strain PK84 of a blue-g reen alga Anabaena variabilis growing in a vanadium-containing medium under the conditions providing for autotrophic growth and nitrogen fixation has been studied. A characteristic of this mutant was a certain lesion in the h ydrogenase system responsible for the utilization of H-2. Unlike the wild-t ype strain of Anabaena variabilis ATCC29413, H-2 evolution by A. variabilis PK84 cells depended only to a very little extent on the O-2 content in the external medium. Even in an argon atmosphere, the rate of this process mar kedly exceeded the corresponding rate exhibited by the wild-type strain of A. variabilis. Under periodically changed growth conditions, the rate of H- 2 evolution by a young culture of A. variabilis PK84 in the argon atmospher e amounted to 90-100 mu mol/(mg Chl a h). The mutant was able to continuous ly generate H-2 under periodical growth conditions in a spiral tubular phot obioreactor with a volume of 4.35 1. A maximum rate of H-2 evolution by the culture of A. variabilis PK84 under these conditions with a growth medium bubbled with air containing 2% CO2 amounted to 0.01 ml/(ml suspension h) at 36 degrees C, a PFD of 332 mu E/(m(2) s), and an optical density of the al gal culture corresponding to 19-20 mu g Chl a/ml. The results obtained allo w us to conclude that, among the known species of blue-green algae, the mut ant A. variabilis PK84 has the highest efficiency of photobiological H-2 pr oduction. The effect of light intensity on H-2 production by A. variabilis PK84 and its physiological characteristics is discussed.