Comparison of mesophilic and thermophilic anaerobic hydrogen production by hot spring enrichment culture

Anaerobic hydrogen producing mesophilic and thermophilic cultures were enriched and studied from an intermediate temperature (45 °C) hot spring sample. H2 production yields at 37 °C and 55 °C were highest at the initial pH of 6.5 and 7.5, respectively. Optimum glucose, iron and nickel concentrations were 9 g/l, 25 mg/l and 25 mg/l both at 37 °C and 55 °C, respectively. The highest H2 yields at 37 °C and 55 °C were 1.8 and 1.0 mol H2/mol glucose, respectively, with the optimal pH, glucose concentration and iron addition. Hydrogen production from glucose at 55 °C and 37 °C was associated with ethanol- and acetate–butyrate type fermentations, respectively. Bacterial composition was analyzed by 16S rRNA gene-targeted denaturing gradient gel electrophoresis (DGGE). Clostridium species dominated at both temperatures and the microbial diversity decreased with increasing temperature. At 55 °C, Clostridium ramosum was the dominant organism.