Abstract
BackgroundSugarcane bagasse (SCB) is an abundant feedstock for second-generation bioethanol production. This complex biomass requires an array of carbohydrate active enzymes (CAZymes), mostly from filamentous fungi, for its deconstruction to monomeric sugars for the production of value-added fuels and chemicals. In this study, we evaluated the repertoire of proteins in the secretome of a catabolite repressor-deficient strain of Penicillium funiculosum, PfMig188, in response to SCB induction and examined their role in the saccharification of SCB.ResultsA systematic approach was developed for the cultivation of the fungus with the aim of producing and understanding arrays of enzymes tailored for saccharification of SCB. To achieve this, the fungus was grown in media supplemented with different concentrations of pretreated SCB (0–45 g/L). The profile of secreted proteins was characterized by enzyme activity assays and liquid chromatography–tandem mass spectrometry (LC–MS/MS). A total of 280 proteins were identified in the secretome of PfMig188, 46% of them being clearly identified as CAZymes. Modulation of the cultivation media with SCB up to 15 g/L led to sequential enhancement in the secretion of hemicellulases and cell wall-modifying enzymes, including endo-β-1,3(4)-glucanase (GH16), endo-α-1,3-glucanase (GH71), xylanase (GH30), β-xylosidase (GH5), β-1,3-galactosidase (GH43) and cutinase (CE5). There was ~ 122% and 60% increases in β-xylosidase and cutinase activities, respectively. There was also a 36% increase in activities towards mixed-linked glucans. Induction of these enzymes in the secretome improved the saccharification performance to 98% (~ 20% increase over control), suggesting their synergy with core cellulases in accessing the recalcitrant region of SCB.ConclusionOur findings provide an insight into the enzyme system of PfMig188 for degradation of complex biomass such as SCB and highlight the importance of adding SCB to the culture medium to optimize the secretion of enzymes specific for the saccharification of sugarcane bagasse.
Highlights
Sugarcane bagasse (SCB) is an abundant feedstock for second-generation bioethanol production
The results show that the alkaline pretreatment was effective to reducing the lignin content in the biomass, thereby increasing the cellulose content in the recovered substrate while marginally affecting the total hemicellulose content
It was noticed that there was no significant change in the overall hemicellulose content after the alkaline pretreatment, analysis of the monosaccharides from the non-cellulosic polysaccharides including hemicelluloses and pectins showed a change in the sugar profile after pretreatment (Table 1)
Summary
Sugarcane bagasse (SCB) is an abundant feedstock for second-generation bioethanol production This complex biomass requires an array of carbohydrate active enzymes (CAZymes), mostly from filamentous fungi, for its deconstruction to monomeric sugars for the production of value-added fuels and chemicals. Sugarcane bagasse (SCB), a crushed fibrous residue of sugarcane stalks remaining after juice extraction, is one of Ogunyewo et al Biotechnol Biofuels (2021) 14:171 the largest cellulosic agro-industrial wastes produced in many countries with a worldwide annual production of approximately 54 million tons [3] It is a readily available by-product of sugar processing mills whose valorization will have a long-lasting effect on the sustenance of sugar mills, which are struggling to keep their profit margins reasonably high. This integrated enzyme production approach uses incoming lignocellulosic biomass as substrate for on-site enzyme production [8,9,10]
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