A xylose-fermenting yeast hybridized by intergeneric fusion between Saccharomyces cerevisiae and Candida intermediamutants for ethanol production

Abstract

Background: Bioethanol production from lignocellulosic biomass, in particular xylose, is currently of great concern, given the abundance of this sugar in the world, because Saccharomyces cerevisiae, which is widely used for bioethanol production, is unable to naturally ferment xylose. The aim of this study was to obtain a novel yeast capable of stably producing ethanol from biomass containing xylose by protoplast fusion between S. cerevisiae and xylose-utilizing yeast. Results: We describe a novel xylose-fermenting yeast strain, FSC1, developed for ethanol production by intergeneric hybridization between S. cerevisiae and Candida intermedia mutants by using a protoplast fusion technique. The characteristics of the FSC1 strain are reported with respect to xylose fermentation, morphology, gene, and protein expression. Mutation of the parental strains prior to protoplast fusion endowed the FSC1 strain with the ability to convert xylose to ethanol. Microscopic analysis confirmed that the parental and FSC1 strains produced spores in the potassium acetate medium. The FSC1 strain is uninucleate diploid, has a stable metabolism, and expresses proteins at a higher level than the parental strains. We found that FSC1 strain could stably achieve an ethanol yield of 0.38 g/g-substrate in fermentation of a mixture of glucose and xylose. In addition, the fermentation ability of FSC1was improved by successive chemical mutation, resulting in a higher ethanol yield of 0.42 g/g-substrate, corresponding to 82% theoretical yield. Conclusions:The mutation-fusion technique we have described here is very useful for the development of intergeneric hybrids capable of xylose fermentation, and the FSC strains generated using this technique have the potential for industrial use in ethanol production from lignocellulosic biomass.

Encapsulation enhances protoplast fusant stability

“…Genomic stability in encapsulated cells results from placing limits on cell division. With little chance for their nuclei to segregate, encapsulated fusants are much more stable than has been reported previously (Kahar & Tanaka, 2014). This feature may facilitate their use in a variety of applications, ranging from the production of amylase enzymes (Pandey et al, 2000) to oil recovery (S. Sun et al, 2013) and even to microbial weed control (TeBeest, 2012).…”

Strain improvement of native Saccharomyces cerevisiae LN ITCC 8246 strain through protoplast fusion to enhance its xylose uptake

“…It is a significant tool for genetic manipulation as it resolves the barrier to genetic exchange imposed by conventional mating systems. It is particularly useful for industrially important microorganisms [13,14,15]. Random mutagenesis by protoplast fusion of intergeneric yeast strains has been carried out earlier [16,17,18].…”

Molecular Genetic Characterization of Fusants from Protoplast Fusion of S. Cerevisiae and P. Stipitis ATCC 58785

“…Protoplast fusion is a conventional technique even though it has been shown to be successful for strain enhancement and it is seen as significant in constructing yeast strains as it mitigates the challenges of genetic modification enforced by traditional mating systems and supports the movement of sizeable segments of genomic DNA. Protoplast fusion is a common approach used to improve fermentation of industrial yeast strains [1][2][3]. The ease of the technical application in addition to the materials needed for this approach makes protoplast fusion the most extensively employed technique of transformation in fungi.…”