Carbon sources and XlnR-dependent transcriptional landscape of CAZymes in the industrial fungus Talaromyces versatilis: when exception seems to be the rule

Abstract

BackgroundResearch on filamentous fungi emphasized the remarkable redundancy in genes encoding hydrolytic enzymes, the similarities but also the large differences in their expression, especially through the role of the XlnR/XYR1 transcriptional activator. The purpose of this study was to evaluate the specificities of the industrial fungus Talaromyces versatilis, getting clues into the role of XlnR and the importance of glucose repression at the transcriptional level, to provide further levers for cocktail production.ResultsBy studying a set of 62 redundant genes representative of several categories of enzymes, our results underlined the huge plasticity of transcriptional responses when changing nutritional status. As a general trend, the more heterogeneous the substrate, the more efficient to trigger activation. Genetic modifications of xlnR led to significant reorganisation of transcriptional patterns. Just a minimal set of genes actually fitted in a simplistic model of regulation by a transcriptional activator, and this under specific substrates. On the contrary, the diversity of xlnR+ versus ΔxlnR responses illustrated the existence of complex and unpredicted patterns of co-regulated genes that were highly dependent on the culture condition, even between genes that encode members of a functional category of enzymes. They notably revealed a dual, substrate-dependant repressor-activator role of XlnR, with counter-intuitive transcripts regulations that targeted specific genes. About glucose, it appeared as a formal repressive sugar as we observed a massive repression of most genes upon glucose addition to the mycelium grown on wheat straw. However, we also noticed a positive role of this sugar on the basal expression of a few genes, (notably those encoding cellulases), showing again the strong dependence of these regulatory mechanisms upon promoter and nutritional contexts.ConclusionsThe diversity of transcriptional patterns appeared to be the rule, while common and stable behaviour, both within gene families and with fungal literature, the exception. The setup of a new biotechnological process to reach optimized, if not customized expression patterns of enzymes, hence appeared tricky just relying on published data that can lead, in the best scenario, to approximate trends. We instead encourage preliminary experimental assays, carried out in the context of interest to reassess gene responses, as a mandatory step before thinking in (genetic) strategies for the improvement of enzyme production in fungi.Electronic supplementary materialThe online version of this article (10.1186/s12934-019-1062-8) contains supplementary material, which is available to authorized users.

CAZymes from the thermophilic fungus Thermoascus aurantiacus are induced by C5 and C6 sugars

“…The high level of CAZyme production when feeding purified sugars illuminates previous studies of fungal gene expression and enzymatic activity, which reported that simple sugars such as d -xylose, cellobiose and l- arabinose during batch fermentations weakly induced cellulases and xylanases compared to complex polysaccharides such as xylan and lignocellulosic plant biomass in T. aurantiacus [ 9 ], A. niger [ 15 ] and Talaromyces versatilis [ 46 ] . These studies might have found stronger induction effects of the simple sugars on cellulases and xylanases expression when applying continuous feeding as we observed for T. aurantiacus .…”

“…Nevertheless, it is widely established that complex substrates induce a broader variety of CAZymes [ 14 ]. Feeding mixtures of sugars or hydrolysates may generate more efficacious enzyme formulations without adding solid substrates to the fermentation medium [ 46 – 48 ].…”

Unveiling Xylanolytic Enzymes Production of Talaromyces wortmannii DR49 on Industrial Agro Wastes

“…In β-xylosidase production the highest titration observed were for WB (0.57 U/mL) and xylose (0.34 U/mL) at 144 h. Xylose was not able to induce xylanase production, although this saccharide seems to play a role in β-xylosidase production. Llanos and coauthors [27] studied the influence of carbon source in the transcriptional levels of glicohydrolase genes in Talaromyces versatilis and verified that xylose did not induce dose-dependent inhibitory effect for xylanases and β-xylosidase synthesis.…”

The Secretomes of Aspergillus japonicus and Aspergillus terreus Supplement the Rovabio® Enzyme Cocktail for the Degradation of Soybean Meal for Animal Feed

“…Its complete hydrolysis requires the complementary action of more than 30 CAZymes [ 48 ]. Previous studies have shown that the Rovabio ® enzymatic cocktail displays a limited number of CAZymes acting on pectin, with only GH28 polygalacturonases, GH78 rhamnosidases, and GH53 endo-galactanases [ 24 , 26 , 27 ]. This suggests that the Aspergilli secretomes may contain specific CAZymes targetting pectin that are absent in the Rovabio ® cocktail.…”

“…These fungal secretomes have allowed the development of industrial enzymatic cocktails, including in the animal feed field. The Rovabio ® is an enzymatic cocktail produced from the ascomycete fungus Talaromyces versatilis [ 24 ]. The Rovabio ® cocktail contains more than 200 different enzymes, mostly carbohydrate-active enzymes (CAZymes; [ 25 ]), which target the different components of plant cell wall, cellulose, and hemicelluloses [ 26 ].…”