Metabolic engineering industrial yeast strains for efficient hemicellulosic bioethanol production

摘要

The constant increase of fossil fuels consumption, raising their prices, andenvironmental concerns derived of its use has stimulated the search for new renewableenergy sources. Lignocellulose raw materials (LCMs) derived from agricultural, industrialand forest biomass can be a source of environmental, economic and strategic benefits,avoiding the competition with food production, when used as sustainable feedstock. [1]Nevertheless, lignocellulosic processing to obtain fermentable sugars involves apretreatment that generates inhibitor compounds of fermentation process and sugars asxylose which cannot be naturally consumed by Saccharomyces cerevisiae. Therefore, thepursuit for robust microorganisms in order to design sustainable processes for cellulosicand hemicellulosic bioethanol production is one of the main challenges for a cost-effectivelignocellulosic biofuels. The use of natural robust yeast strains can overcome inhibitorseffect, as they are known for a higher fermentation capacity and stress tolerance relatedwith harsh industrial processes like high sugar and ethanol concentrations, elevatedtemperatures, pH variations and presence of toxic compounds. [2] In addition, previousstudies from our group have identified key genes necessary for yeast growth and maximalfermentation rate in hydrolysates [3,4]. Strains with robust genetic backgrounds have beenshown to already demonstrate enhanced background expression of several genes involvedin the detoxification of some of these inhibitors [5], but different genetic backgrounds haveshown to present diverse responses. [4] On the other hand, the inhibitory load oflignocellulosic hydrolysates, which varies depending on the raw material and operationalconditions of pretreatment [6], has been shown to differentially influence the consequenceof genetic manipulations [4], highlighting the importance of evaluating their effect underprocess-like conditions. In this sense, the aim of this work was to evaluate the effect ofxylose metabolic engineering on different background yeast strains isolated from industrialenvironments (cachaça distilleries and first and second bioethanol industries) usingseveral pretreated lignocellulosic feedstocks.