Exopolysaccharide synthesis repressor genes (exoR and exoX) related to curdlan biosynthesis by Agrobacterium sp

Curdlan is a neutral, water-insoluble, unbranched, linear β-(1,3)-glucan. This study explored the roles of exoR and exoX in curdlan biosynthesis in Agrobacterium sp. ATCC 31749. The microcapsule biosynthesis of ΔexoR strain was reduced, and the motility of this strain increased remarkably compared with the wild-type (WT) strain during the cell growth phase. The curdlan yields of ΔexoR and ΔexoX strains enhanced by 19% and 17%, and the glucose utilization increased by 12% and 11%, respectively, compared with the WT strain during batch fermentation. By contrast, the curdlan yields of exoR and exoX overexpression strains decreased by 28% and 33%, respectively. The gel strength produced by ΔexoR and exoX overexpression strains decreased compared with the WT strain. RT-qPCR analysis at the transcriptional level revealed that key genes in exopolysaccharide synthesis and central metabolic pathways were up-regulated in ΔexoX and ΔexoR strains during gel production. Metabolomics analysis of ΔexoR and ΔexoX mutants proved the rates of central metabolic and electron transport chain were accelerated.