pilA Gene Contributes to Virulence, Motility, Biofilm Formation, and Interspecific Competition of Bacteria in Acidovorax citrulli

, the causative agent of bacterial fruit blotch, can be divided into two main groups based on factors such as pathogenicity and host species preference. PilA is an important structural and functional component of type IV pili (T4P). Previous studies have found significant differences in DNA sequences between group I and group II strains of . In this study, we characterized in the group I strain pslb65 and the group II strain Aac5. mutants, complementation strains, and cross-complementation strains were generated, and their biological phenotypes were analyzed to identify functional differences between in the two groups. deletion mutants (pslb65 Δ and Aac5 Δ ) showed significantly reduced pathogenicity compared with the wild-type (WT) strains; pslb65-Δ also completely lost twitching motility, whereas Aac5-Δ only partially lost motility. In King's B medium, there were no significant differences in biofilm formation between pslb65-Δ and WT pslb65, but Aac5-Δ showed significantly reduced biofilm formation compared to WT Aac5. In M9 minimal medium, both mutants showed significantly lower biofilm formation compared to the corresponding WT strains, although biofilm formation was recovered in the complementation strains. The biofilm formation capacity was somewhat recovered in the cross-complementation strains but remained significantly lower than in the WT strains. The interspecies competitive abilities of pslb65-Δ and Aac5-Δ were significantly lower than in the WT strains; Aac5-Δ was more strongly competitive than pslb65-Δ , and the complementation strains recovered competitiveness to WT levels. Furthermore, the cross-complementation strains showed stronger competitive abilities than the corresponding WT strains. The relative expression levels of genes related to T4P and the type VI secretion system were then assessed in the mutants via quantitative PCR. The results showed significant differences in the relative expression levels of multiple genes in pslb65-Δ and Aac5-Δ compared to the corresponding WT stains. This indicated the presence of specific differences in function between the two groups, but the regulatory mechanisms involved require further study.