Effects of autoinducer-2 mediated quorum sensing on gonadal colonization and reproductive toxicity caused by Aeromonas veronii in loach (Misgurnus anguillicaudatus)

Aeromonas veronii is one of the most common major pathogens in aquaculture, which can infect aquatic animals and cause significant economic losses. Quorum sensing (QS) of A. veronii promotes its intestinal colonization through regulating the production of virulence factors, but little is known about the effects of QS systems on the gonadal colonization of A. veronii. In this study, transcriptomic analysis of intestinal tissues in loaches after infection with A. veronii revealed the enrichment of reproductive-related genes between the wild strain A. veronii Z12 and the QS deficient mutant strain Z12ΔluxS treatment groups. The results indicated that A. veronii might colonize the gonads of loaches and cause damage through an autoinducer-2 (AI-2) mediated-QS mechanism. Through quantitative analysis of intestinal permeability and tight junction protein-related genes, it was found that A. veronii could break through the intestinal barrier. Furthermore, fluorescence signal detection revealed that A. veronii entered and colonized the gonads through the bloodstream. Analysis of gonadal tissue sections showed that A. veronii infection caused tissue lesions and induced apoptosis, resulting in damage to the gonads. The estradiol-testosterone (E₂/T) ratio was disturbed, as indicated by the detection of sex hormone levels, which further demonstrating the damage caused by A. veronii infection on the reproductive ability of loaches. This study provides new insights into the promotional impact of the AI-2 mediated QS system on the toxic effects of A. veronii to the reproductive capacity of loach, which is crucial for the healthy cultivation of aquatic organisms.