Phylogenetic and physiological studies of four hydrogen-producing thermoanareobes from Icelandic geothermal areas

Hydrogen production capacities of four new thermophilic bacteria (AK 1 , AK 14 , AK 15 and AK 17 ) isolated from Icelandic geothermal areas were investigated. All isolates were saccharolytic and degrading various monoand disaccharides. One strain, AK 17 , degraded cellulose and pectin, at least partially, as well as the amino acids serine and threonine. Strain AK 1 degraded pectin and xylan to some extent. Product formation from glucose fermentation was in all cases acetate, hydrogen and carbon dioxide and one or two of the following: ethanol, butyrate and lactate. Strain AK 1 produced 0.58 to 0.77 mol H 2 per mol of degraded carbohydrates in batch cultures. The values for strains AK 14 , AK 15 and AK 17 ranged from 0.83-1.14, 0.46-1.27 and 0.16-0.70 mol H 2 per mol hexose degraded, respectively. The hydrogen production rates varied from 0.56 mmol H 2 l -1 h