Abstract
BackgroundGenomic and proteomic analysis are potent tools for metabolic characterization of microorganisms. Although cellulose usually triggers cellulase production in cellulolytic fungi, the secretion of the different enzymes involved in polymer conversion is subjected to different factors, depending on growth conditions. These enzymes are key factors in biomass exploitation for second generation bioethanol production. Although highly effective commercial cocktails are available, they are usually deficient for β-glucosidase activity, and genera like Penicillium and Talaromyces are being explored for its production.ResultsThis article presents the description of Talaromyces amestolkiae as a cellulase-producer fungus that secretes high levels of β-glucosidase. β-1,4-endoglucanase, exoglucanase, and β-glucosidase activities were quantified in the presence of different carbon sources. Although the two first activities were only induced with cellulosic substrates, β-glucosidase levels were similar in all carbon sources tested. Sequencing and analysis of the genome of this fungus revealed multiple genes encoding β-glucosidases. Extracellular proteome analysis showed different induction patterns. In all conditions assayed, glycosyl hydrolases were the most abundant proteins in the supernatants, albeit the ratio of the diverse enzymes from this family depended on the carbon source. At least two different β-glucosidases have been identified in this work: one is induced by cellulose and the other one is carbon source-independent. The crudes induced by Avicel and glucose were independently used as supplements for saccharification of slurry from acid-catalyzed steam-exploded wheat straw, obtaining the highest yields of fermentable glucose using crudes induced by cellulose.ConclusionsThe genome of T. amestolkiae contains several genes encoding β-glucosidases and the fungus secretes high levels of this activity, regardless of the carbon source availability, although its production is repressed by glucose. Two main different β-glucosidases have been identified from proteomic shotgun analysis. One of them is produced under different carbon sources, while the other is induced in cellulosic substrates and is a good supplement to Celluclast in saccharification of pretreated wheat straw.
Highlights
Genomic and proteomic analysis are potent tools for metabolic characterization of microorganisms
Protein g377 was the most abundant in media containing slurry, glucose, or xylan, representing 72, 55, and 45% of the total BGLUs, respectively, while in Avicel, the main BGLU was protein g3821 (70%). Low amounts of this enzyme were produced in media with glucose (
Genome sequencing and annotation disclosed a high number of genes encoding BGLUs, which suggests the relevance of these enzymes for this organism
Summary
Genomic and proteomic analysis are potent tools for metabolic characterization of microorganisms. Cellulose usually triggers cellulase production in cellulolytic fungi, the secretion of the different enzymes involved in polymer conversion is subjected to different factors, depending on growth conditions. These enzymes are key factors in biomass exploitation for second generation bioethanol production. Second generation bioethanol represents an efficient alternative to conventional energy supply, involving the exploitation of renewable sources, usually disposable wastes from other industrial or agricultural activities. In this process, polysaccharides from lignocellulosic biomass are hydrolyzed to glucose and xylose units that are further converted to ethanol [1]. Cellulose is a homopolysaccharide of β-1,4-linked d-glucose residues whose enzymatic conversion into free glucose requires the coordinated work of the cellulase system, consisting of three different kinds of hydrolases: (1) cellobiohydrolases (CBH) named as exoglucanases, which cleave cellobiose units from the chain ends, (2) β-1,4-endoglucanases (EG), which hydrolyze the polymers internally, reducing their degree of polymerization and (3) β-glucosidases (BGLU), which convert cellobiose and soluble cellodextrins into glucose [4]
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