# Methionine inducing carbohydrate esterase secretion of Trichoderma harzianum enhances the accessibility of substrate glycosidic bonds

## TL;DR

Adding ammonium sulfate boosts the ability of Trichoderma harzianum to break down plant biomass by increasing carbohydrate esterase activity, improving access to glycosidic bonds.

## Contribution

Reveals a methylation-regulated pathway in T. harzianum that enhances deacetylation through up-regulation of carbohydrate esterases.

## Key findings

- Ammonium sulfate induces up-regulation of multiple carbohydrate esterases (CE3/CE4/CE15/CE16) in T. harzianum.
- A differentially methylated region in the ThgsfR2 promoter is linked to lignocellulolytic response and Thce3 expression.
- Increased deacetylation improves polysaccharide hydrophilicity and glycosidic bond accessibility.

## Abstract

The conversion of plant biomass into biochemicals is a promising way to alleviate energy shortage, which depends on efficient microbial saccharification and cellular metabolism. Trichoderma spp. have plentiful CAZymes systems that can utilize all-components of lignocellulose. Acetylation of polysaccharides causes nanostructure densification and hydrophobicity enhancement, which is an obstacle for glycoside hydrolases to hydrolyze glycosidic bonds. The improvement of deacetylation ability can effectively release the potential for polysaccharide degradation.

Ammonium sulfate addition facilitated the deacetylation of xylan by inducing the up-regulation of multiple carbohydrate esterases (CE3/CE4/CE15/CE16) of Trichoderma harzianum. Mainly, the pathway of ammonium-sulfate's cellular assimilates inducing up-regulation of the deacetylase gene (Thce3) was revealed. The intracellular metabolite changes were revealed through metabonomic analysis. Whole genome bisulfite sequencing identified a novel differentially methylated region (DMR) that existed in the ThgsfR2 promoter, and the DMR was closely related to lignocellulolytic response. ThGsfR2 was identified as a negative regulatory factor of Thce3, and methylation in ThgsfR2 promoter released the expression of Thce3. The up-regulation of CEs facilitated the substrate deacetylation.

Ammonium sulfate increased the polysaccharide deacetylation capacity by inducing the up-regulation of multiple carbohydrate esterases of T. harzianum, which removed the spatial barrier of the glycosidic bond and improved hydrophilicity, and ultimately increased the accessibility of glycosidic bond to glycoside hydrolases.

The online version contains supplementary material available at 10.1186/s12934-024-02394-1.