Gallic acid enhances honeybee larvae resistance to Paenibacillus larvae infections: Insights from molecular docking, bacterial community modulation, and whole-genome sequencing.

Abstract

American foulbrood (AFB) disease, caused by the bacterium Paenibacillus larvae, is a devastating disease affecting honeybee (Apis mellifera L.) populations worldwide. Commonly treated with antibiotics, which have negative impacts on both honeybees and the environment, there is an urgent need for alternatives in AFB control. This study aimed to investigate the effects of gallic acid (GA) on honeybee larvae challenged with P. larvae spores and explore its modulation of larval microbiota. Our results demonstrated that in the presence of P. larvae spores, coadministration of 125 µg/mL GA significantly increased the survival rate and body weight of honeybee larvae. Molecular docking analyses revealed that GA competitively binds to spore germination proteins YndE and GerM, with affinities comparable to L-tyrosine and stronger than uric acid, respectively, suggesting interference with P. larvae spore germination. 16S rRNA gene amplicon sequencing revealed that GA treatment augmented bacterial diversity and enriched lactic acid bacteria (LAB) in honeybee larvae. Whole-genome sequencing of 2 LAB strains, Apilactobacillus kunkeei GL-2 and Enterococcus faecium GL-6, isolated from GA-treated larvae, unveiled their potential to produce antimicrobial secondary metabolites and bacteriocins, which may contribute to their competitive advantages against P. larvae. Notably, the E. faecium GL-6 strain possessed genes encoding gallate decarboxylase, enabling GA utilization, and 2 putative bacteriocinogenic genetic clusters for enterolysin A and enterocin L50 a/b. These findings suggest that GA and the GL-6 strain hold potential as preventive measures against AFB disease in honeybees through modulation of gut microbiota and competitive inhibition of P. larvae.