Nutrient-supplemented propagation of Saccharomyces cerevisiae improves its lignocellulose fermentation ability

Abstract

Propagation conditions have been shown to be of considerable importance for the fermentation ability of Saccharomyces cerevisiae. The limited tolerance of yeast to inhibitors present in lignocellulosic hydrolysates is a major challenge in second-generation bioethanol production. We have investigated the hypothesis that the addition of nutrients during propagation leads to yeast cultures with improved ability to subsequently ferment lignocellulosic materials. This hypothesis was tested with and without short-term adaptation to wheat straw or corn stover hydrolysates during propagation of the yeast. The study was performed using the industrial xylose-fermenting S. cerevisiae strain CR01. Adding a mixture of pyridoxine, thiamine, and biotin to unadapted propagation cultures improved cell growth and ethanol yields during fermentation in wheat straw hydrolysate from 0.04 g g −1 to 0.19 g g −1 and in corn stover hydrolysate from 0.02 g g −1 to 0.08 g g −1. The combination of short-term adaptation and supplementation with the vitamin mixture during propagation led to ethanol yields of 0.43 g g −1 in wheat straw hydrolysate fermentation and 0.41 g g −1 in corn stover hydrolysate fermentation. These ethanol yields were improved compared to ethanol yields from cultures that were solely short-term adapted (0.37 and 0.33 g g −1). Supplementing the propagation medium with nutrients in combination with short-term adaptation was thus demonstrated to be a promising strategy to improve the efficiency of industrial lignocellulosic fermentation.

RNA sequencing reveals metabolic and regulatory changes leading to more robust fermentation performance during short-term adaptation of Saccharomyces cerevisiae to lignocellulosic inhibitors

“…In our previous work, we noted the importance of detoxification of the medium from aldehydes to allow the growth of S. cerevisiae [ 18 ]. Therefore, the differential expression of genes encoding oxidoreductases that have been shown to have activity on furfural and HMF was investigated.…”

“…6 B), are genes encoding proteins involved in the synthesis of the thiamin precursor hydroxymethylpyrimidine [ 66 ]. In a previous study, we showed that supplementing non-adapting cultures with a mixture of thiamin and pyridoxine improves fermentation performance in hydrolysate-containing medium [ 18 ]. Apart from a protein of unknown function (DPA10), three out of four genes that showed a trend of down-regulation (Fig.…”

“…To investigate whether metabolic pathways are transcriptionally perturbed as a result of short-term lignocellulosic adaptation, up- and down-regulated genes were analyzed in the context of their metabolic pathways (see Methods section). In particular, we evaluated the changes in fatty acid metabolism due to the potential implications on plasma membrane composition [ 77 ], as well as biotin and thiamine as we have previously shown that these improve the productivity of lignocellulosic bioethanol-producing fermentation when added to the culture during the propagation step [ 18 ].…”

“…ROS are thought to be involved in the decrease in cell viability, and thus the lower ethanol productivity at elevated ethanol concentrations [ 16 ]. In a parallel or additional strategy to short-term adaptation, the addition of antioxidants such as the B vitamins thiamin and biotin, and the antioxidant glutathione has been shown to improve ethanol productivity in hydrolysate fermentation [ 5 , 17 , 18 ]. These different antioxidants are believed to act as sinks for ROS or regenerators of NADPH through various mechanisms, thereby relieving inhibitor stress.…”

Fermented Parkia biglobosa seeds as a nitrogen source supplementation for bioethanol production from cashew apple juice

“…) and vitamins (e.g., thiamine (B1), pyridoxine (B6), biotin (B7), riboflavin, nicotinic acid (B3), pantothenic acid (B5), etc. ), which significantly impact yeast growth, stress tolerance, ethanol yield, and secondary synthesis of fermentation metabolites (Venkateshwar et al, 2010;Perli et al, 2020;van Dijk et al, 2020). Moreover, nitrogen compounds such as amino acids and proteins stimulate yeast growth and improve fermentation kinetics.…”