Characterization of glucose/non-glucose-tolerant β-glucosidases from the metatranscriptome in compost

Abstract

Functional microbial communities producing β-glucosidases differentially regulate the expression of glucose/non-glucose-tolerant β-glucosidases in response to carbon catabolite repression (CCR), which is a common phenomenon. To better understand their biological roles in a composting environment, four representative β-glucosidase genes were cloned from the metatranscriptome of the compost for expression and characterization. BGLA contains conserved sites Trp168 and Leu173, associated with glucose tolerance. In the presence of 100 mM glucose, BGLA's hydrolysis activity increases by 80%. BGLB also contains Trp168 and Leu173; however, its hydrolysis activity is significantly inhibited by glucose. On the contrary, Trp168 of BGLC was replaced by Phe, yet its hydrolysis activity increased by 20% in the presence of 25 mM glucose. However, BGLD did not exhibit any enzymatic activity. Molecular docking and dynamic simulations revealed the structural basis of glucose tolerance. Metatranscriptomic analysis of the four genes showed that functional microbial communities upregulated or downregulated gene expression in response to different CCR environments to maintain overall carbon metabolic balance. These findings demonstrate that the enzymatic activity characteristics of individual glucose/non-glucose-tolerant β-glucosidases are consistent with their transcriptional regulation under CCR in the complex composting environment.