Abstract
Bioethanol production from lignocellulosic biomass has received increasing attention over the past decade. Many attempts have been made to reduce the cost of bioethanol production by combining the separate steps of the process into a single-step process known as consolidated bioprocessing. This requires identification of organisms that can efficiently decompose lignocellulose to simple sugars and ferment the pentose and hexose sugars liberated to ethanol. There have been many attempts in engineering laboratory strains by adding new genes or modifying genes to expand the capacity of an industrial microorganism. There has been less attention in improving bioethanol-related processes utilizing natural variation existing in the natural ecotypes. In this study, we sought to identify genomic loci contributing to variation in saccharification of cellulose and fermentation of glucose in the fermenting cellulolytic fungus Neurospora crassa through quantitative trait loci (QTL) analysis. We identified one major QTL contributing to fermentation of glucose and multiple putative QTL’s underlying saccharification. Understanding the natural variation of the major QTL gene would provide new insights in developing industrial microbes for bioethanol production.
Highlights
Fermentation of cellulosic biomass by microorganisms is a complex process requiring coordinated regulation of multiple pathways, including production and secretion of at least three distinct classes of catabolic enzymes, transport of substrates into the cell, followed by catabolism and fermentation of the resultant monomeric C5 and C6 sugars
We have identified that there exists a substantial variation in bioethanolrelated traits in the mapping population, N6
We identified a few major candidate genes with the potential to contribute to the observed variation, including the clustered glucose metabolism genes on Linkage Group (LG) I for fermentation, and transcriptional regulators vib-1 and xlr-1 on LG II and LG IV, respectively, for saccharification
Summary
Fermentation of cellulosic biomass by microorganisms is a complex process requiring coordinated regulation of multiple pathways, including production and secretion of at least three distinct classes of catabolic enzymes (cellulase, hemicellulase, and lignin peroxidase enzymes), transport of substrates into the cell, followed by catabolism and fermentation of the resultant monomeric C5 and C6 sugars. While many researchers attempt to engineer existing strains by introducing the genes for pathways lacking in the given organisms, success has been limited due to the increased physiological burdens imposed by genetic manipulation. There are, organisms that already possess the genetic elements needed to perform all of the requisite processes, such as the model filamentous fungus Neurospora crassa [9]. These types of native microorganisms present excellent potential sources of useful industrial enzymes and products. Breeding has proven to be a reliable method for manipulating genomes to select for desired traits, as evidenced by the successes of plant breeding [6]. Selective breeding has been used in fungi in attempts to select for increased saccharification and fermentation potential [9]
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