Optimization of cellobiohydrolase production and secretome analysis of Trametes villosa LBM 033 suitable for lignocellulosic bioconversion

Pure lignin induces overexpression of cytochrome P450 (CYP) encoding genes and brings insights into the lignocellulose depolymerization by Trametes villosa

Trametes villosa is a remarkable white-rot fungus (WRF) with the potential to be applied in lignocellulose conversion to obtain chemical compounds and biofuels. Lignocellulose breakdown by WRF is carried out through the secretion of oxidative and hydrolytic enzymes. Despite the existing knowledge about this process, the complete molecular mechanisms involved in the regulation of this metabolic system have not yet been elucidated. Therefore, in order to understand the genes and metabolic pathways regulated during lignocellulose degradation, the strain T. villosa CCMB561 was cultured in media with different carbon sources (lignin, sugarcane bagasse, and malt extract). Subsequently, biochemical assays and differential gene expression analysis by qPCR and high-throughput RNA sequencing were carried out. Our results revealed the ability of T. villosa CCMB561 to grow on lignin (AL medium) as the unique carbon source. An overexpression of Cytochrome P450 was detected in this medium, which may be associated with the lignin O-demethylation pathway. Clusters of up-regulated CAZymes-encoding genes were identified in lignin and sugarcane bagasse, revealing that T. villosa CCMB561 acts simultaneously in the depolymerization of lignin, cellulose, hemicellulose, and pectin. Furthermore, genes encoding nitroreductases and homogentisate-1,2-dioxygenase that act in the degradation of organic pollutants were up-regulated in the lignin medium. Altogether, these findings provide new insights into the mechanisms of lignocellulose degradation by T. villosa and confirm the ability of this fungal species to be applied in biorefineries and in the bioremediation of organic pollutants.

Low-cost homemade cocktails for enzymatic conversion of sugarcane and cassava bagasses

The agricultural industries generate lignocellulosic wastes that can be modified by fungi to generate high value-added products. This work aimed to analyze the efficiency and the cost-effectiveness of the bioconversion of sugarcane and cassava bagasses using low-cost homemade enzymatic cocktails from Aspergillus niger LBM 134. Both bagasses were pretreated with a soft alkaline solution without any loss of polysaccharides. After the hydrolysis, a 28% of conversion to glucose and 42% to xylose were reached in the hydrolysis of sugarcane bagasse while an 80% of saccharification yield, in the hydrolysis of cassava bagasse using the homemade enzymes. Furthermore, a more disorganised surface and no starch granules were observed in the sugarcane and cassava bagasses, respectively. The bioethanol yield from sugarcane and casava bagasses was predicted to be 4.16 mg mL-1 and 2.57 mg mL-1, respectively. A comparison of the cost of the homemade and the commercial enzymes was carried out. Similar hydrolysis percentages were achieved employing any enzyme; however, it was 1000-2000 times less expensive using the homemade cocktails than using the commercial enzymes. Therefore, the cost of obtaining glucose from bagasses was most expensive when applying the commercial enzymes. Moreover, the hydrolysis of the cassava bagasse was most efficient with the homemade cocktails. The importance and novelty of this work lie in the similar performance and the lower cost of the homemade cocktails from the fungus A. niger LBM 134 compared with the commercial enzymes on the hydrolysis of the sugarcane and cassava bagasses.

Exoproteomic Study and Transcriptional Responses of Laccase and Ligninolytic Peroxidase Genes of White-Rot Fungus Trametes hirsuta LE-BIN 072 Grown in the Presence of Monolignol-Related Phenolic Compounds

Being an abundant renewable source of aromatic compounds, lignin is an important component of future bio-based economy. Currently, biotechnological processing of lignin through low molecular weight compounds is one of the conceptually promising ways for its valorization. To obtain lignin fragments suitable for further inclusion into microbial metabolism, it is proposed to use a ligninolytic system of white-rot fungi, which mainly comprises laccases and peroxidases. However, laccase and peroxidase genes are almost always represented by many non-allelic copies that form multigene families within the genome of white-rot fungi, and the contributions of exact family members to the overall process of lignin degradation has not yet been determined. In this article, the response of the Trametes hirsuta LE-BIN 072 ligninolytic system to the presence of various monolignol-related phenolic compounds (veratryl alcohol, p-coumaric acid, vanillic acid, and syringic acid) in culture media was monitored at the level of gene transcription and protein secretion. By showing which isozymes contribute to the overall functioning of the ligninolytic system of the T. hirsuta LE-BIN 072, the data obtained in this study will greatly contribute to the possible application of this fungus and its ligninolytic enzymes in lignin depolymerization processes.