Adaptive evolution of Kluyveromyces marxianus MTCC1389 for high ethanol tolerance

Abstract

Kluyveromyces marxianus has several benefits over Saccharomyces cerevisiae with respect to thermotolerance and the capacity to convert lactose to ethanol and several sugars. Currently, K. marxianus vulnerable ethanol tolerance makes it unsuitable for commercial use, and further research is needed to augment its ethanol resistance and its pivotal mechanisms. To date, very few studies have been done to improve its ethanol tolerance. The present study is aimed to improve K. marxianus ethanol tolerance using adaptive evolutionary engineering. Presently, ethanol tolerance of the parent K. marxianus MTCC1389 strain was only 8% (v/v), therefore, adaptive evolution, a sequential transfer with an increase in stress, was performed to increase its tolerance towards ethanol. It took 110 days to improve its ethanol tolerance to 12% (v/v). With this, ethanol production was 110.51 ± 0.87 g L−1 in 46 h which was 42.9% higher than the parent strain (78.33 ± 0.88 g L−1). The specific growth rate was also enhanced from 0.043 h−1 to 0.049 h−1 in the ethanol adapted strain. In 5 cycles of serial re-pitching there was insignificant reduction in ethanol production from 1st cycle (110.47 ± 0.12) to 5 cycle (105.59 ± 0.25). The stability of the strain was up to 10 cycles of subculturing in low sugar medium and ethanol production was 109.05 ± 0.26 g L−1. Hence, adaptation was able to improve K. marxianus MTCC1389 ethanol tolerance and its ethanol production significantly.