Abstract
The evolutionary adaptation was approached on the thermotolerant yeast Kluyveromyces marxianus NIRE-K3 at 45oC on xylose as a sole source of carbon for enhancement of xylose uptake. After 60 cycles, evolved strain K. marxianus NIRE-K3.1 showed comparatively 3.75-fold and 3.0-fold higher specific growth and xylose uptake rates, respectively than that of native strain. Moreover, the short lag phase was also observed on adapted strain. During batch fermentation with xylose concentration of 30 g l-1, K. marxianus NIRE-K3.1 could utilize about 96 % of xylose in 72 h and produced 4.67 and 15.7 g l-1 of ethanol and xylitol, respectively, which were 9.72-fold and 4.63-fold higher than that of native strain. Similarly, specific sugar consumption rate, xylitol and ethanol yields were 5.07-fold, 1.15-fold and 2.44-fold higher as compared to the native strain, respectively. The results obtained after evolutionary adaptation of K. marxianus NIRE-K3 show the significant improvement in the xylose utilization, ethanol and xylitol yields, and productivities. By understanding the results obtained, the significance of evolutionary adaptation has been rationalized, since the adapted culture could be more stable and could enhance the productivity.
Highlights
Several environmental issues including global warming, climate change, CO2, and CO emission are major concern nowadays, which are primarily caused by conventional transportation fuels and burning of the crop residues (Kumar et al, 2009)
Potential of adapted strain K. marxianus NIRE-K3.1 for xylose uptake during growth and fermentation was compared with native strain
Kluyveromyces marxianus NIRE-K3 was adapted for enhanced xylose utilization through sequential culturing in YEPX medium containing 20 g l−1 xylose
Summary
Several environmental issues including global warming, climate change, CO2, and CO emission are major concern nowadays, which are primarily caused by conventional transportation fuels and burning of the crop residues (Kumar et al, 2009). A thermotolerant yeast have various advantages over mesophiles including higher rate of saccharification and fermentation, utilization of broad range of substrates and less energy requirement for mixing and product recovery, and lower cost of pumping and steering (Kumar et al, 2010; Rodrussamee et al, 2011; Zhang et al, 2013; Sharma et al, 2016). Evolutionary adaptation together with genetic engineering can be a better approach to develop the sustainable and economic process (Behera et al, 2016; Kuyper et al, 2005; Liu and Hu, 2010; Zhou et al, 2012; Sharma et al, 2016) This strategy has already been implemented along with various conventional techniques including protein engineering, intergeneric hybridization, and metabolic engineering (Kuhad et al, 2011; Zhang et al, 2015).
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