A novel D-xylose isomerase: from the gut of a wood feeding beetle for improved conversion in Saccharomyces cerevisiae

Abstract

Carbohydrate rich substrates such as lignocellulosic hydrolysates remain one of the primary sources of potentially renewable fuel and bulk chemicals. The pentose sugar D-xylose is often present in significant amounts along with hexoses. For low value/high volume products, yield is of paramount importance for process economy. Saccharomyces cerevisiae can acquire the ability to metabolize D-xylose through expression of heterologous D-xylose isomerase (XI). This enzyme is notoriously difficult to express in S. cerevisiae and only fourteen genes have been reported to be active so far. We cloned a new D-xylose isomerase derived from microorganisms in the gut of the wood-feeding beetle Odontotaenius disjunctus. Although somewhat homologous to the current gold-standard from Piromyces sp. E2, metagenome scaffold gene neighborhoods and metagenome binning identified the gene as of bacterial in origin and the host as a Parabacteroides sp. Expression of the new XI enzyme in S. cerevisiae resulted in faster aerobic growth on D-xylose than the XI from Piromyces. The D-xylose isomerization rate of the yeast expressing this new XI was also 72 % higher. Interestingly, increasing concentrations of xylitol (up to 8 g/L) appeared not to inhibit xylose consumption in both strains. The newly described XI displayed 2.6 times higher specific activity, 37 % higher affinity for D-xylose, and exhibited higher activity over a broader temperature range, retaining 51 % of maximal activity at 30 ºC compared with only 29% activity for the Piromyces XI. This new enzyme represents a highly valuable addition to the S. cerevisiae molecular toolbox and shows promise for improved industrial conversion of carbohydrates.