Microbial production of hydrogen: An overview

Production of hydrogen by anaerobes, facultative anaerobes, aerobes, methylotrophs, and photosynthetic bacteria is possible. Anaerobic Clostridia are potential producers and immobilized C. butyricum produces 2 mol H-2/mol glucose at 50% efficiency. Spontaneous production of H-2 from formate and glucose by immobilized Escherichia coli showed 100% and 60% efficiencies, respectively. Enterobactericiae produces H-2 at similar efficiency from different monosaccharides during growth. Among methylotrophs, methanogenes, rumen bacteria, and thermophilic archae, Ruminococcus albus, is promising (2.37 mol/mol glucose). Immobilized aerobic Bacillus licheniformis optimally produces 0.7 mol H-2/mol glucose. Photosynthetic Rhodospirillum rubrum produces 4, 7, and 6 mol of H-2 from acetate, succinate, and malate, respectively. Excellent productivity (6.2 mol H-2/mol glucose) by co-cultures of Cellulomonas with a hydrogenase uptake (Hup) mutant of R. capsulata on cellulose was found. Cyanobacteria, viz., Anabaena, Synechococcus, and Oscillatoria sp., have been studied for photoproduction of H-2. Immobilized A. cylindrica produces H-2 (20 ml/g dry wt/h) continually for 1 year. Increased H-2 productivity was found for Hup(-) mutant of A. variabilis. Synechococcus sp. has a high potential for H-2 production in fermenters and outdoor cultures. Simultaneous productions of oxychemicals and H-2 by Klebseilla sp. and by enzymatic methods were also attempted. The fate of H-2 biotechnology is presumed to be dictated by the stock of fossil fuel and state of pollution in future.