Fermentation of glucose-xylose-arabinose mixtures by a synthetic consortium of single-sugar-fermenting Saccharomyces cerevisiae strains

Abstract

d-Glucose, d-xylose and l-arabinose are major sugars in lignocellulosic hydrolysates. This study explores fermentation of glucose-xylose-arabinose mixtures by a consortium of three 'specialist' Saccharomyces cerevisiae strains. A d-glucose- and l-arabinose-tolerant xylose specialist was constructed by eliminating hexose phosphorylation in an engineered xylose-fermenting strain and subsequent laboratory evolution. A resulting strain anaerobically grew and fermented d-xylose in the presence of 20 g L-1 of d-glucose and l-arabinose. A synthetic consortium that additionally comprised a similarly obtained arabinose specialist and a pentose non-fermenting laboratory strain, rapidly and simultaneously converted d-glucose and l-arabinose in anaerobic batch cultures on three-sugar mixtures. However, performance of the xylose specialist was strongly impaired in these mixed cultures. After prolonged cultivation of the consortium on three-sugar mixtures, the time required for complete sugar conversion approached that of a previously constructed and evolved 'generalist' strain. In contrast to the generalist strain, whose fermentation kinetics deteriorated during prolonged repeated-batch cultivation on a mixture of 20 g L-1d-glucose, 10 g L-1d-xylose and 5 g L-1l-arabinose, the evolved consortium showed stable fermentation kinetics. Understanding the interactions between specialist strains is a key challenge in further exploring the applicability of this synthetic consortium approach for industrial fermentation of lignocellulosic hydrolysates.

Laboratory Evolution of a Saccharomyces cerevisiae × S. eubayanus Hybrid Under Simulated Lager-Brewing Conditions

“…At first glance, loss of the ability to utilize maltotriose, an abundant fermentable sugar in wort, appears to be undesirable from an evolutionary perspective. However, as demonstrated in studies on laboratory evolution of S. cerevisiae in sequential batch cultures on sugar mixtures, the selective advantage of consuming a specific sugar from a sugar mixture correlates with the number of generations of growth on that sugar during each cultivation cycle (Wisselink et al, 2009; Verhoeven et al, 2018). Saccharomyces yeasts, including strain IMS0408 generally prefer glucose and maltose over maltotriose (Alves et al, 2008; Hebly et al, 2015; Brickwedde et al, 2017).…”

Xylose utilization stimulates mitochondrial production of isobutanol and 2-methyl-1-butanol in Saccharomyces cerevisiae

“…We also tested YZy197 fermentations using Verduyn’s medium, a vitamin-enriched minimal medium that uses only ammonium salts as nitrogen source [37]. This medium has been effectively used for yeast xylose assimilation [38, 39] and isobutanol production from xylose [40]. Time course experiments (as described above), in 10 mL of CaCO 3 -buffered medium with 10% xylose (see “Methods”), revealed that YZy197 still produces significant amounts of isobutanol and 2-MbOH (Additional file 1: Figure S5c), although at slightly lower titers and productivities compared to those obtained in SC-Ura, 10% xylose (Fig.…”

Synthetic Biology Tools to Engineer Microbial Communities for Biotechnology

“…The conversion of lignocellulosic sugars into high value products is additionally hindered by the competitive inhibition of D-xylose transporters by D-glucose [72]. A three-strain consortium of S. cerevisiae that ferments glucose, xylose, and arabinose overcame this limitation by engineering each strain to ferment only one of the three sugars, resulting in a consortium significantly more stable than a generalist strain [73].…”