Abstract
BackgroundAn economically viable production of biofuels and biochemicals from lignocellulose requires microorganisms that can readily convert both the cellulosic and hemicellulosic fractions into product. The yeast Candida intermedia displays a high capacity for uptake and conversion of several lignocellulosic sugars including the abundant pentose d-xylose, an underutilized carbon source since most industrially relevant microorganisms cannot naturally ferment it. Thus, C. intermedia constitutes an important source of knowledge and genetic information that could be transferred to industrial microorganisms such as Saccharomyces cerevisiae to improve their capacity to ferment lignocellulose-derived xylose.ResultsTo understand the genetic determinants that underlie the metabolic properties of C. intermedia, we sequenced the genomes of both the in-house-isolated strain CBS 141442 and the reference strain PYCC 4715. De novo genome assembly and subsequent analysis revealed C. intermedia to be a haploid species belonging to the CTG clade of ascomycetous yeasts. The two strains have highly similar genome sizes and number of protein-encoding genes, but they differ on the chromosomal level due to numerous translocations of large and small genomic segments. The transcriptional profiles for CBS 141442 grown in medium with either high or low concentrations of glucose and xylose were determined through RNA-sequencing analysis, revealing distinct clusters of co-regulated genes in response to different specific growth rates, carbon sources and osmotic stress. Analysis of the genomic and transcriptomic data also identified multiple xylose reductases, one of which displayed dual NADH/NADPH co-factor specificity that likely plays an important role for co-factor recycling during xylose fermentation.ConclusionsIn the present study, we performed the first genomic and transcriptomic analysis of C. intermedia and identified several novel genes for conversion of xylose. Together the results provide insights into the mechanisms underlying saccharide utilization in C. intermedia and reveal potential target genes to aid in xylose fermentation in S. cerevisiae.
Highlights
An economically viable production of biofuels and biochemicals from lignocellulose requires micro‐ organisms that can readily convert both the cellulosic and hemicellulosic fractions into product
Xylose-fermenting yeasts can serve as a source of knowledge and genes for xylose uptake and assimilation which may be transferrable to other microorganisms including S. cerevisiae that are better suited as industrial workhorses
We report here on the complete genome sequence of C. intermedia, its transcriptional response to xylose and glucose and the identification of several novel genes with potential to contribute to xylose conversion in lignocellulose-based production of biofuels and biochemicals
Summary
An economically viable production of biofuels and biochemicals from lignocellulose requires micro‐ organisms that can readily convert both the cellulosic and hemicellulosic fractions into product. The yeast Candida intermedia displays a high capacity for uptake and conversion of several lignocellulosic sugars including the abundant pentose d-xylose, an underutilized carbon source since most industrially relevant microorganisms cannot naturally ferment it. A number of native xylose-fermenting yeasts (e.g. Scheffersomyces stipitis, Spathaspora passalidarum, Sugiyamaella lignohabitans, and Candida tenuis) have been identified and characterized to various degrees in terms of metabolism, physiology, genomics and proteomics. Their usefulness for lignocellulosic conversion processes has been explored, but as cell factories they are limited by their (i) dependence on micro-aerobic conditions for fermentative metabolism, (ii) low tolerance to lignocellulosic inhibitors and (iii) poor overall fermentation titers [4, 5]. Xylose-fermenting yeasts can serve as a source of knowledge and genes for xylose uptake and assimilation which may be transferrable to other microorganisms including S. cerevisiae that are better suited as industrial workhorses
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