THE BIOTECHNOLOGY OF HYDROGEN-PRODUCTION BY NOSTOC FLAGELLIFORME GROWN UNDER CHEMOSTAT CONDITIONS

The potential of using N-2-fixing cyanobacteria to produce hydrogen ph otobiologically has stimulated research on the physiology and biotechn ology of species exhibiting high H-2 production rates over long period s of time. In this work Nostoc flagelliforme, a terrestrial N-2-fixing cyanobacterium, has been examined to establish its physiology and pot ential for H-2 production under controlled conditions. Cell filaments of N. flagelliforme were purified and grown in liquid culture to optim ize its H-2 metabolism. In batch-grown cultures the activity of nitrog enase, the key enzyme for H-2 production in N-2-fixing organisms, was found to be high only during a short phase of exponential growth. A ch emostat system was thus constructed for long-term experiments using co ntinuous cultures, with the aim of exploiting the exponential growth p hase. The dilution rate (D) and environmental factors, such as N-2 con centration in the gas phase and temperature, significantly influenced H-2 production. Cells grown continuously under the optimized condition s of D = 0.022 h(-1), 34 degrees C and 5.1 kPa N-2 in the gas phase ex hibited H-2 production rates that were more than four times higher tha n the maximal rates under standard batch growth conditions.