Ethanol adaptation in a thermotolerant yeast strain Kluyveromyces marxianus IMB3

The maximum ethanol concentration produced from glucose in defined media at 45 degrees C by the thermotolerant yeast Kluyveromyces marxianus IMB3 was 44 g L-1. Acclimatisation of the strain through continuous culture at ethanol concentrations up to 80 g L-1, shifted the maximum ethanol concentration at which growth was observed from 40 g L-1 to 70 g L-1. Four isolates were selected from the continuous culture, only one of which produced a significant increase in final ethanol concentration (50 +/- 0.4 g L-1), however in subsequent fermentations, following storage on nutrient agar plates, the maximum ethanol concentration was comparable with the original isolate, The maximum specific ethanol production rates (approximately 1.5 g (gh)(-1)) were also comparable with the original strain except for one isolate (0.7 g (gh)(-1)). The specific ethanol productivity decreased with ethanol concentration; this decrease correlated linearly (rval 0.92) with cell viability. Due to the transience of induced ethanol tolerance in the strain it was concluded that this was not a valid method for improving final ethanol concentrations or production rates.