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

Abstract

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 EtOHproducing thermophilic microorganisms derived from hot spring environments in Iceland. Hydrogen-and EtOHproducing 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.

Biohydrogen production from wheat straw hydrolysate by dark fermentation using extreme thermophilic mixed culture

“…During steady state period (days 32-39), acetate concentration was increased, while lactate concentration was significantly decreased, which resulted in higher hydrogen production with a yield of 178.0 AE 10.1 mL-H 2 / g-sugars. Similar tendencies reported in the literature, moderate-to high hydrogen yields (78.0-414.0 mL-H 2 /gsugars) were achieved when acetate was the dominant metabolic pathway Kotsopoulos et al, 2006;Yokoyama et al, 2009;Zheng et al, 2008), while lower hydrogen yields of 21.2 and 52.3 mL-H 2 /g-sugars, respectively, were associated with higher lactate concentration and coincident with unstable or overloading conditions (Koskinen et al, 2008;Liu et al, 2008a). Lignocellulosic biofuel production is not yet economically competitive with fossil fuels, therefore, a successful utilization of all sugars is important for improving the overall economy (Hallenbeck et al, 2009).…”

Production of Biofuels from Cellulose of Woody Biomass

“…It was reported that the optimized pH for producing hydrogen in a dark fermentation is between 5.5 and 6.7 [102]. However, there are contradictory reports about the influence of ethanol on hydrogen production in dark fermentation processes in that some studies reported a possible competition between ethanol and hydrogen production [103][104][105], while others reported a high hydrogen production accompanied by a high ethanol production [106,107]. In another study, the addition of ethanol to the growth medium at the initiation of the fermentation process resulted in 54% H2 and 25% acetate increases, respectively, using C. Thermocellum bacteria [108].…”

Discovery and Characterization of a Thermostable Esterase from an Oil Reservoir Metagenome

“…However, studies of these microbes are limited by difficulties in accessing relevant oil reservoirs, as well as technical challenges in representative oil reservoir sampling [4] [5]. Due to their nature, oil reservoir microorganisms with their special adaptations are potential high value targets for the discovery of useful biocatalysts for industrial processes [6]- [8]. By also covering the genetic information of the vast uncultivable fraction of microorganisms in nature [1] which is particularly pronounced in such special ecological niches, metagenomic libraries are an invaluable source for new discoveries by bioprospecting, using both metagenomic sequence data and cloned metagenomic DNA [9] [10].…”