Bioprospecting Thermophilic Microorganisms from Icelandic Hot Springs for Hydrogen and Ethanol Production

Fermentations can be used to produce sustainable energy carriers, such as hydrogen and ethanol (EtOH), from biomass or organic waste materials. The aim of this research was to prospect efficient H 2 - and EtOH-producing thermophilic microorganisms derived from hot spring environments in Iceland. Hydrogen- and EtOH-producing enrichment cultures were obtained from various hot spring samples over a temperature range of 50–78 °C. The temperature dependencies for the most promising enrichments were determined with a temperature-gradient incubator. One of the enrichments (33HL) produced 2.10 mol of H 2 /mol of glucose at 59 °C. Another enrichment (9HG), dominated by bacteria closely affiliated with Thermoanaerobacter thermohydrosulfuricus, produced 0.68 mol of H 2 /mol of glucose, and 1.21 mol of EtOH/mol of glucose at 78 °C. Hydrogen and EtOH production by 9HG was characterized further in a continuous-flow bioreactor at 74 °C. The highest H 2 and EtOH yields of 9HG were obtained at pH 6.8 ± 0.3. Lactate production decreased the H 2 and EtOH yields in the continuous-flow bioreactor, and the yields were lower than those obtained in the batch fermentations. In conclusion, the thorough batch screening of Icelandic hot spring samples indicated some promising enrichments for H 2 or H 2 plus EtOH production from carbohydrate materials.