Genetic engineering and raising temperature enhance recombinant protein production with the cdna1 promoter in Trichoderma reesei

Teredinibacter turnerae secretome highlights key enzymes for plant cell wall degradation

Carbohydrate-active enzymes (CAZymes) are crucial in the sustainable production of fuels and raw materials from recalcitrant plant cell wall polysaccharides (PCWPs). Teredinibacter turnerae, a symbiont of wood-boring shipworms, is a prolific degrader of plant biomass, largely due to the extensive CAZyme repertoire in its genome. To identify key enzymes involved in PCWP utilization, we analyzed the secretomes of T. turnerae E7MBN strain grown on sucrose, major PCWPs (cellulose, xylan, and pectin), and residual rice hull biomass using mass spectrometry-based proteomics. Our results show that T. turnerae E7MBN exhibits minimal enzyme secretion across various carbon sources, where secretomes mostly display similar functional profiles. Enzymatic complexity varied with the substrate, with cellulose-grown secretome being the most complex and comprising the majority of secreted CAZymes. These CAZymes contain domains that primarily target cellulose, hemicellulose, or pectin, notably including multicatalytic enzymes that are consistently found in the secretome and are likely central to biomass degradation. In contrast, the xylan-grown secretome displayed a more specific response, secreting only a single bifunctional hemicellulase, E7_MBN_00081, also identified as a core component of the bacteria's enzymatic repertoire. Meanwhile, the pectin-grown secretome consists of multiple tonB-dependent receptors, which, along with isomerases, are considered common secretome constituents. E7MBN also demonstrated the capability to utilize rice hull biomass, predominantly secreting proteins previously identified under cellulose. Protein-protein interaction network analysis further revealed functional associations between CAZymes and several uncharacterized proteins, which include CBM-containing redox enzymes and a putative xylan-acting protein, thus offering new insights into their potential role in lignocellulose degradation. Overall, our work contributes to our understanding of enzymatic strategies employed by T. turnerae for PCWP deconstruction and highlights its potential as a promising source of CAZymes for sustainable biomass conversion.

Co-production of sugars and aroma compounds from tobacco waste using biomass-degrading enzymes produced by Aspergillus brunneoviolaceus Ab-10

Biomass-degrading enzymes produced by microorganisms have a great potential in the processing of agricultural wastes. In order to produce suitable biomass-degrading enzymes for releasing sugars and aroma compounds from tobacco scraps, the feasibility of directly using the scraps as a carbon source for enzyme production was investigated in this study. By comparative studies of ten fungal strains isolated from tobacco leaves, Aspergillus brunneoviolaceus Ab-10 was found to produce an efficient enzyme mixture for the saccharification of tobacco scraps. Proteomic analysis identified a set of plant biomass-degrading enzymes in the enzyme mixture, including amylases, hemicellulases, cellulases and pectinases. At a substrate concentration of 100 g/L and enzyme dosage of 4 mg/g, glucose of 17.6 g/L was produced from tobacco scraps using the crude enzyme produced by A. brunneoviolaceus Ab-10. In addition, the contents of 23 volatile molecules, including the aroma compounds 4-ketoisophorone and benzyl alcohol, were significantly increased after the enzymatic treatment. The results provide a strategy for valorization of tobacco waste by integrating the production of biomass-degrading enzymes into the tobacco scrap processing system.

Small GTPase Rab7 is involved in stress adaptation to carbon starvation to ensure the induced cellulase biosynthesis in Trichoderma reesei

BACKGROUND

The saprophytic filamentous fungus Trichoderma reesei represents one of the most prolific cellulase producers. The bulk production of lignocellulolytic enzymes by T. reesei not only relies on the efficient transcription of cellulase genes but also their efficient secretion after being translated. However, little attention has been paid to the functional roles of the involved secretory pathway in the high-level production of cellulases in T. reesei. Rab GTPases are key regulators in coordinating various vesicle trafficking associated with the eukaryotic secretory pathway. Specifically, Rab7 is a representative GTPase regulating the transition of the early endosome to the late endosome followed by its fusion to the vacuole as well as homotypic vacuole fusion. Although crosstalk between the endosomal/vacuolar pathway and the secretion pathway has been reported, the functional role of Rab7 in cellulase production in T. reesei remains unknown.

RESULTS

A TrRab7 was identified and characterized in T. reesei. TrRab7 was shown to play important roles in T. reesei vegetative growth and vacuole morphology. Whereas knock-down of Trrab7 significantly compromised the induced production of T. reesei cellulases, overexpression of the key transcriptional activator, Xyr1, restored the production of cellulases in the Trrab7 knock-down strain (Ptcu-rab7KD) on glucose, indicating that the observed defective cellulase biosynthesis results from the compromised cellulase gene transcription. Down-regulation of Trrab7 was also found to make T. reesei more sensitive to various stresses including carbon starvation. Interestingly, overexpression of Snf1, a serine/threonine protein kinase known as an energetic sensor, partially restored the cellulase production of Ptcu-rab7KD on Avicel, implicating that TrRab7 is involved in an energetic adaptation to carbon starvation which contributes to the successful cellulase gene expression when T. reesei is transferred from glucose to cellulose.

CONCLUSIONS

TrRab7 was shown to play important roles in T. reesei development and a stress response to carbon starvation resulting from nutrient shift. This adaptation may allow T. reesei to successfully initiate the inducing process leading to efficient cellulase production. The present study provides useful insights into the functional involvement of the endosomal/vacuolar pathway in T. reesei development and hydrolytic enzyme production.

Structure-guided engineering of transcriptional activator XYR1 for inducer-free production of lignocellulolytic enzymes in Trichoderma reesei

The filamentous fungus Trichoderma reesei is widely used for the production of lignocellulolytic enzymes in industry. XYR1 is the major transcriptional activator of cellulases and hemicellulases in T. reesei. However, rational engineering of XYR1 for improved lignocellulolytic enzymes production has been limited by the lack of structure information. Here, alanine 873 was identified as a new potential target for the engineering of XYR1 based on its structure predicted by AlphaFold2. The mutation of this residue to tyrosine enabled significantly enhanced production of xylanolytic enzymes in the medium with cellulose as the carbon source. Moreover, xylanase and cellulase production increased by 56.7- and 3.3-fold, respectively, when glucose was used as the sole carbon source. Under both conditions, the improvements of lignocellulolytic enzyme production were higher than those in the previously reported V821F mutant. With the enriched hemicellulases and cellulases, the crude enzymes secreted by the A873Y mutant strain produced 51 % more glucose and 52 % more xylose from pretreated corn stover than those of the parent strain. The results provide a novel strategy for engineering the lignocellulolytic enzyme-producing capacity of T. reesei, and would be helpful for understanding the molecular mechanisms of XYR1 regulation.