Effect of temperature on ethanol tolerance of a thermophilic anaerobic ethanol producer Thermoanaerobacter A10: Modeling and simulation

The low ethanol tolerance of thermophilic anaerobic bacteria (<2%, v/v) is a major obstacle for their industrial exploitation for ethanol production. The ethanol tolerance of the thermophilic anaerobic ethanol‐producing strain Thermoanaerobacter A10 was studied during batch tests of xylose fermentation at a temperature range of 50–70°C with exogenously added ethanol up to ∼6.4% (v/v). At the optimum growth temperature of 70°C, the strain was able to tolerate 4.7% (v/v) ethanol, and growth was completely inhibited at 5.6% (v/v). A higher ethanol tolerance was found at lower temperatures. At 60°C, the strain was able to tolerate at least 5.1% (v/v) ethanol. A generalized form of Monod kinetic equation proposed by Levenspiel was used to describe the ethanol (product) inhibition. The model predicted quite well the experimental data for the temperature interval 50–70°C, and the maximum specific growth rate and the toxic power ( n ), which describes the order of ethanol inhibition at each temperature, were estimated. The toxic power ( n ) was 1.33 at 70°C, and corresponding critical inhibitory product concentration ( P crit ) above which no microbial growth occurs was determined to be 5.4% (v/v). An analysis of toxic power ( n ) and P crit showed that the optimum temperature for combined microbial growth and ethanol tolerance was 60°C. At this temperature, the toxic power ( n ), and P crit were 0.50, and 6.5% (v/v) ethanol, respectively. From a practical point of view, the model may be applied to compare the ethanol inhibition (ethanol tolerance) on microbial growth of different thermophilic anaerobic bacterial strains. Biotechnol. Bioeng. 2007;98: 1161–1170. © 2007 Wiley Periodicals, Inc.