Mechanisms for hydrogen production by different bacteria during mixed-acid and photo-fermentation and perspectives of hydrogen production biotechnology

H-2 has a great potential as an ecologically-clean, renewable and capable fuel. It can be mainly produced via hydrogenases (Hyd) by different bacteria, especially Escherichia coli and Rhodobacter sphaeroides. The operation direction and activity of multiple Hyd enzymes in E. coli during mixed-acid fermentation might determine H-2 production; some metabolic crosstalk between Hyd enzymes is proposed. Manipulating the activity of different Hyd enzymes is an effective way to enhance H-2 production by E. coli in biotechnology. Moreover, a novel approach would be the use of glycerol as feedstock in fermentation processes leading to H-2 production. Mixed carbon (sugar and glycerol) utilization studies enlarge the kind of organic wastes used in biotechnology. During photo-fermentation under limited nitrogen conditions, H-2 production by Rh. sphaeroides is observed when carbon and nitrogen sources are supplemented. The relationship of H-2 production with H+ transport across the membrane and membrane-associated ATPase activity is shown. On the other hand, combination of carbon sources (succinate, malate) with different nitrogen sources (yeast extract, glutamate, glycine) as well as different metal (Fe, Ni, Mg) ions might regulate H-2 production. All these can enhance H-2 production yield by Rh. sphaeroides in biotechnology Finally, two of these bacteria might be combined to develop and consequently to optimize two stages of H-2 production biotechnology with high efficiency transformation of different organic sources.