Abstract
BackgroundHigh-temperature fermentation technology with thermotolerant microbes has been expected to reduce the cost of bioconversion of cellulosic biomass to fuels or chemicals. Thermotolerant Kluyveromyces marxianus possesses intrinsic abilities to ferment and assimilate a wide variety of substrates including xylose and to efficiently produce proteins. These capabilities have been found to exceed those of the traditional ethanol producer Saccharomyces cerevisiae or lignocellulose-bioconvertible ethanologenic Scheffersomyces stipitis.ResultsThe complete genome sequence of K. marxianus DMKU 3-1042 as one of the most thermotolerant strains in the same species has been determined. A comparison of its genomic information with those of other yeasts and transcriptome analysis revealed that the yeast bears beneficial properties of temperature resistance, wide-range bioconversion ability, and production of recombinant proteins. The transcriptome analysis clarified distinctive metabolic pathways under three different growth conditions, static culture, high temperature, and xylose medium, in comparison to the control condition of glucose medium under a shaking condition at 30°C. Interestingly, the yeast appears to overcome the issue of reactive oxygen species, which tend to accumulate under all three conditions.ConclusionsThis study reveals many gene resources for the ability to assimilate various sugars in addition to species-specific genes in K. marxianus, and the molecular basis of its attractive traits for industrial applications including high-temperature fermentation. Especially, the thermotolerance trait may be achieved by an integrated mechanism consisting of various strategies. Gene resources and transcriptome data of the yeast are particularly useful for fundamental and applied researches for innovative applications.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-015-0227-x) contains supplementary material, which is available to authorized users.
Highlights
High-temperature fermentation technology with thermotolerant microbes has been expected to reduce the cost of bioconversion of cellulosic biomass to fuels or chemicals
K. marxianus has a number of advantages over K. lactis or S. cerevisiae, including the intrinsic fermentation capability of various sugars at high temperatures [4,12,13], weak glucose repression that is preferable for mixed sugars such as hemicellulose hydrolysate, and fermentability of inulin [13,14]
Genomic information and comparative genomics The genome sequence of K. marxianus DMKU 3-1042 was precisely determined by nucleotide sequencing with three different sizes of shotgun libraries
Summary
High-temperature fermentation technology with thermotolerant microbes has been expected to reduce the cost of bioconversion of cellulosic biomass to fuels or chemicals. Thermotolerant Kluyveromyces marxianus possesses intrinsic abilities to ferment and assimilate a wide variety of substrates including xylose and to efficiently produce proteins. These capabilities have been found to exceed those of the traditional ethanol producer Saccharomyces cerevisiae or lignocellulose-bioconvertible ethanologenic Scheffersomyces stipitis. K. marxianus is a haploid, homothallic, thermotolerant, hemiascomycetous yeast [6,7] and a close relative of Kluyveromyces lactis, a model Crabtree-negative yeast [8,9,10,11] Both yeasts share the assimilating capability of lactose, which is absent from Saccharomyces cerevisiae. Draft genome sequences of three K. marxianus strains have been published [7,17,18], but no detailed analysis is available
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