Abstract
The consequences of the overuse of antibiotics in aquaculture have intensified the search for alternative pathogen control strategies, including postbiotics and antimicrobial proteins. In this study, we evaluated the potential of extracellular products (ECPs) from Bacillus pumilus UMA 169 and UMA 216, cultivated in media supplemented with microalgal and cyanobacterial biomass, to inhibit biofilm formation, engage in quorum quenching (QQ), and modulate virulence in key aquaculture pathogens. Our findings show that most of the tested ECPs, with the exception of MICRO 216, significantly inhibited biofilm formation by Aeromonas hydrophila and Vibrio anguillarum . However, all ECPs downregulated the expression of aip56 , a key virulence gene in Photobacterium damselae subsp. piscicida. They also modulated the transcription of iron acquisition genes ( hutB, hutD, irp1, irp2 ), suggesting a broader impact on bacterial virulence. These findings highlight the potential of B. pumilus -derived ECPs as both biofilm inhibitors and virulence modulators for aquaculture pathogens. Further studies should explore their application as postbiotic agents in pathogen control strategies aiming to reduce antibiotic overuse and improve fish health in aquaculture systems.