Microbial Production of Hydrogen: An Overview

Abstract

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 H₂/mol glucose at 50% efficiency. Spontaneous production of H₂ from formate and glucose by immobilized Escherichia coli showed 100% and 60% efficiencies, respectively. Enterobactericiae produces H₂ at similar efficiency from different mono-saccharides 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 H₂/mol glucose. Photosynthetic Rhodospirillum rubrum produces 4, 7, and 6 mol of H₂ from acetate, succinate, and malate, respectively. Excellent productivity (6.2 mol H₂/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 H₂. Immobilized A. cylindrica produces H₂ (20 ml/g dry wt/h) continually for 1 year. Increased H₂ productivity was found for Hup-mutant of A. variabilis. Synechococcus sp. has a high potential for H₂ production in fermentors and outdoor cultures. Simultaneous productions of oxychemicals and H₂ by Klebseilla sp. and by enzymatic methods were also attempted. The fate of H₂ biotechnology is presumed to be dictated by the stock of fossil fuel and state of pollution in future.