Adaptive evolution of an industrial strain of Saccharomyces cerevisiae for combined tolerance to inhibitors and temperature

Abstract

IntroductionDevelopment of industrial yeast strains with high tolerance towards the inhibitors released during biomass pretreatment is critical for bioethanol production. Combining this trait with increased thermotolerance would result in a more efficient production via Simultaneous Saccharification and Fermentation (SSF) as well as reduced cooling costs. The aim of the present work was to develop a yeast strain combining these traits.ResultsUsing a long-term adaptation strategy a stable Saccharomyces cerevisiae isolate (ISO12) was evolved from the industrial strain Ethanol Red (ER). ISO12, contrary to the parental strain, is capable of growing and fermenting the liquid fraction of non-detoxified spruce hydrolysate at 39°C with an ethanol yield of 0.38 g ethanol . g hexoses-1. In contrast with previous studies, the superior phenotype of ISO12 does not rely on higher reductase activities for furaldehyde inhibitor conversion, but rather on a higher thermotolerance. ISO12 shows a higher capacity to ferment hydrolysate at 39°C and higher viability during heat-shock at 52°C than ER. In the absence of inhibitors, however, both ER and ISO12 displayed similar growth phenotype at 39°C.ConclusionsThe evolved isolate ISO12 shows a superior phenotype than the parental strain ER when both stresses, temperature and inhibition by hydrolysate-derived compounds, are applied together. The results suggest that the presence of inhibitors depress the maximum temperature permissible for growth to a value below 39°C. As a result of the adaptation process and acquired improved thermotolerance, ISO12 is able to overcome this synergistic effect. Robust strains, such as ISO12, are interesting candidates for second generation ethanol production by SSF, as well as in tropical countries where fermentations at higher temperature can positively impact the production costs.

Adaptive laboratory evolution of ethanologenic Zymomonas mobilis strain tolerant to furfural and acetic acid inhibitors

“…However, little study was focused on development of a furfural-tolerant strain in Z. mobilis. Recently, adaptive laboratory evolution (ALE) emerged as a valuable method in metabolic engineering for strain development and optimization (Chatterjee and Yuan 2006;Conrad et al 2011;Dragosits and Mattanovich 2013;Pál et al 2005;Portnoy et al 2011), which has been successfully used in model organisms, such as Escherichia coli (Hua et al 2007;Lee and Palsson 2010) and Saccharomyces cerevisiae (Cakar et al 2012;Demeke et al 2013;Dhar et al 2011;Wallace-Salinas and Gorwa-Grauslund 2013). ALE is a powerful method to improve certain features of common industrial strains (e.g., inhibitor tolerance, substrate utilization, growth temperature) without requiring knowledge of any underlying genetic mechanisms, as long as the desired trait can be coupled with growth.…”

Adaptation of Desulfovibrio alaskensis G20 to perchlorate, a specific inhibitor of sulfate reduction

“…Paired with the ability of next-generation sequencing to rapidly and economically identify variants, ALE has greatly accelerated our understanding of the underlying mechanisms of adaptation, and has allowed us to link genomic changes to specific phenotypes (Dragosits and Mattanovich, 2013). Apart from basic insight into the adaptation process, ALE has allowed us to probe the mechanism of a variety of stressors and develop strains with industrially relevant phenotypes (Toprak et al, 2012;Wallace-Salinas and Gorwa-Grauslund, 2013;Reyes et al, 2014;Lenski, 2017;Huang and Kao, 2018). This experiment has yielded critical insight into the process of adaptation, its trajectory and replicability and its genetic basis.…”

Bioprospecting thermophilic/thermotolerant microbes for production of lignocellulosic ethanol: A future perspective

“…for the biofuel industry to reduce the overall cost of production. Further, fermentation at high temperature using thermophilic/thermotolerant microorganisms helps in easy ethanol recovery and reduces the chance of contamination which resulted in efficient conversion process for bioethanol production [145,146]. However, no literature was found on the complete economic analysis for bioethanol production using thermophilic/thermotolerant microorganisms.…”