Unlocking cold biomass valorization: Aspartate-mediated upregulation of cellulolytic pathways enhances fungal cold adaptation and straw decomposition

Abstract

Straw fertilization is essential for sustainable agriculture; however, low temperatures in regions like Northeast China hinder straw degradation, leading to residue accumulation. Psychrophilic fungi, predominant in cold environments, are crucial for decomposition under such conditions. In this study, we isolated and characterized two psychrophilic strains, Pseudogymnoascus sp. YL55 and Aspergillus terreus S21, and characterized a cold sensitive and impaired in cellulase mutant named M427 from a T–DNA insertion library of YL55. Molecular analysis indicated that the disrupted gene encodes aspartate aminotransferase (AST). Targeted deletion of the ast gene in both YL55 and S21 led to slow growth of colony and downregulation of lignocellulolytic genes, overexpression Past (OEPast) capable of producing more endonucular and exonucone cellulase. Exogenous aspartate supplementation restored cellulase gene expression and growth defect in ∆Past, and enhanced the expression of cellulase gene and colony growth in mesophilic A. terreus CK48 under cold conditions. Composting trials showed that OEPast + CK48 can promote the rapid start–up of low temperature composting, more reducing sugars and humus were released, which could promote plants growth. Overall, this study shed a novel link between aspartate metabolism, cellulase expression, and cold tolerance, offering potential for engineering robust, cellulose degrading fungi to improve low temperature biomass composting, providing a new biotechnological strategy for other fungi to efficiently decompose straw in winter.