(353c) Strategic Opportunities For Hyperthermophilic Microorganisms And Enzymes In Bioenergy Conversion Processes

The conversion of biomass into ethanol and H₂ by biological routes has been touted as an answer to current problems with energy availability and global warming. In particular, α- and β-glucans represent promising energy feedstocks if bioprocesses based on efficient biocatalysts and microorganisms can be developed to achieve high energy yields and high rates. Biomass conversion at elevated temperatures can take advantage of favorable thermodynamics and accelerated processing rates. As such, hyperthermophilic microorganisms, those that grow optimally at 80°C and higher, represent a strategic opportunity for bioenergy production that merits close examination.

Discussed here will be two model hyperthermophilic microorganisms, Pyrococcus furiosus and Thermotoga maritima, which are being investigated as sources of thermostable and thermoactive enzymes for polysaccharide hydrolysis into fermentable sugars as well as for their capacity to produce biohydrogen from carbohydrate-based feedstocks. A functional genomics approach to biocatalyst discovery is being used to identify ORFs encoding new glucan-hydrolyzing enzymes and to provide clues as to the physiological role of these glycoside hydrolases. Biohydrogen production by these hyperthermophiles was strongly affected by the carbohydrate used as primary carbon/energy source. For P. furiosus, sugar linkage (cellobiose vs. maltose) had a profound effect on bioenergetics, hydrogen generation rates, as well as the transcriptome. For T. maritima, co-fermentation of glucose and xylose was studied and compared to fermentation patterns for the individual sugars. Significant interaction between hexose and pentose processing pathways was found to impact hydrogen production and this observation could be interpreted in terms of transcriptional response analysis. The results presented here point to the potential importance of hyperthermophilic microorganisms for the production of biofuels and the utility of functional genomics approaches for examining metabolic pathways for biohydrogenesis and for the discovery of biocatalysts.