Abstract: YxjA is a highly conserved protein which is synthesized and secreted by organisms ranging from unicellular species to higher plants and animals. It is primarily responsible for the synthesis of purine nucleoside transporters and constitutes a purine riboswitch that negatively regulates the binding to guanine, thereby reversely inhibiting the synthesis of downstream nucleoside transporters. Preliminary library screening assays revealed that the yxjA transposon insertion mutation exhibited a significant reduction in biofilm formation. Utilizing gene homologous recombination and bioinformatics analysis, an yxjA expression-deficient mutant strain, ΔyA, was constructed. Cultivation of the bacterial broth and biofilm formation assays demonstrated that the ΔyA mutant exhibited normal growth but a significantly reduced capacity for biofilm formation. Colonization tests revealed that the ΔyA mutant was significantly impaired in colonizing rice stems. The control efficacy of ΔyA against rice sheath blight was only 21.1%. In this study, the normal formation of bacterial biofilms was used as the screening criterion, and it was found that the YxjA protein significantly positively regulated the biofilm formation intensity and impacted the biocontrol efficacy against fungal diseases, providing a basis for further elucidating the complex regulatory mechanisms of biofilms.

Key words: YxjA protein, biofilm, rice sheath blight, biocontrol