Metabolic profile of wild-type and ethanol-adapted Clostridium thermocellum in continuous culture

Thermophilic anaerobic bacteria such as Clostridium thermocellum have significant advantages relative to yeast in their ability to convert fibrous organic material to vendable chemicals, fuels, and other bioproducts. The adaptation of thermophilic bacteria to ethanol addresses their relatively low ethanol tolerance, one of the technological barriers to efficient biomass conversion. This adaptation has been linked to the bacteria's general response to extreme environments (i.e., temperature, pressure, pH, and organic solvents). The metabolic pathways of wild type (WT) and ethanol adapted (EA) C. thermocellum are quantified and compared as a function of growth rate (dilution rate of 0.05 h^-1) in continuous culture at atmospheric pressure, T = 55°C, and at a cellobiose concentration of 4 g/l with varying concentrations of exogenous ethanol from 0 to 5 % w/v. Metabolite analysis is conducted using capillary electrophoresis (CE)/mass spectrometry. This work represents the first chemostat culture of ethanol-adapted C. thermocellum. Such continuous culture provides steady state metabolic data at controlled growth rates and are useful for modeling. The differences in the metabolic profiles of WT and EA cells in response to growth rate and exogenous ethanol suggests genetic, adaptive, and environmental approaches to maximize the commercial viability of C. thermocellum for biomass conversion.