Diversity and activity of AHL-lactonases in Bacillus spp. from various environments

Disrupting quorum sensing (QS) pathways in animal and plant pathogenic bacteria is an effective strategy to mitigate infections without promoting antibiotic and pesticide resistance. This approach inhibits the production of virulence factors, biofilm formation, and toxin production, reducing bacterial pathogenicity. In plant health protection, Bacillus spp. are extensively researched and utilized as biocontrol agents; however, the potential of their AHL-lactonase-producing ability, which plays a key role as a QS inhibitor of Gram-negative pathogens, remains largely unexplored. This study examined the activity and diversity of QQ enzymes from Bacillus spp. isolates obtained from various natural sources, confirming their presence in previously unreported environments associated with agricultural fields (straw and manure). Our findings show that AiiA lactonase is the most dominant and highly conserved AHL-lactonase among Bacillus isolates from bulk soil, manure, and straw. Despite its sequence conservation, we observed significant variation in AiiA lactonase activities toward the N-hexanoyl-DL-homoserine lactone (C6-HSL) substrate. Furthermore, in silico analysis suggested that the Bacillus sp. YtnP lactonase may have a lower affinity for C6-HSL compared to AiiA lactonase. Finally, this research presents a selection of Bacillus isolates with high AiiA lactonase activity for potential testing against plant pathogens.