Biohydrogen Production by an Ethanol Type Bacterium Oligosphaera ethanolica

The effects of glucose and products inhibition on the growth of an ethanol type fermentation bacterium Oligosphaera ethanolica 8KG-4T in the phylum Lentisphaerae was investigated. Glucose concentration below 3.8 g L-1 was completely converted, while 30 g L-1 glucose completely inhibited the growth and hydrogen production of the pure culture. The addition of hydrogenotrophic methanogen Methanospirllum hungatei improved approximately 2 times higher growth rate compared to that of the pure culture. The coculture with M. hungatei tolerated up to 38 g L-1 glucose and 23% of the glucose was consumed. The addition of 20 mM acetate slightly inhibited the growth and hydrogen production, and 200 mM acetate allowed slow growth and hydrogen production of the pure culture. Compared with acetate, ethanol exhibited more significant inhibition on growth and hydrogen production of O. ethanolica. The addition of 100 mM ethanol had 45% inhibition on the growth and glucose consumption during two weeks of incubation. Inhibition gradually increased with increasing ethanol concentration up to 300 mM, when complete inhibition of glucose consumption occurred. Under high hydrogen partial pressure, the growth and glucose consumption of the pure culture was prolonged. The hydrogen potential with carbohydrates was evaluated. The maximum hydrogen yields were 49.6, 55.7 and 30.7 ml H2/g-xylose in 1, 5 and 10 g L-1, respectively.