Isolation of Quorum Quenching Bacteria from the Euphrates River for Disruption of Biofilm-Forming Aquaculture Pathogens

Radeef, Ziyad K.; Al-Dulimi, Ali G.; Almamoori, Ali Atiyah N.

doi:10.21608/ejabf.2025.393747.6023

Isolation of Quorum Quenching Bacteria from the Euphrates River for Disruption of Biofilm-Forming Aquaculture Pathogens

Document Type : Original Article

Authors

¹ Department of Biotechnology, College of Sciences, University of Diyala, Iraq

² College of Dentistry, University of Bilad Alrafidain

³ Department of Biology, College of Science, University of Diyala, Diyala, Iraq

10.21608/ejabf.2025.393747.6023

Abstract

The development of antibiotic resistant bacterial in aquaculture has stimulated the need for enduring and environmentally friendly bio control tactics. This study examined the presence and efficiency of quorum quenching in bacteria sampled from the Euphrates River as potentially inhibiting the pathogens causing biofilm-forming in fish. The samples collection was conducted from the water and sediment of five impacted aquaculture locations along the Euphrates River. The samples of 97 bacteria were isolated and assessed for quorum quenching activity using the biosensor strains chromo bacterium violaceum CV026, which detects N-acyl homoserine lactone (AHLs) degradation. 16 isolates exhibited quorum quenching ability, and among them, 6 notably inhibited biofilm formation by Aeromonas hydrophila and Vibrio anguillarum, two significant aquaculture pathogens. The most powerful isolate, labeled EQR17, decreased biofilm biomass by 78.6% for A. hydrophila and 71.2% for V. anguillarum. Molecular identification utilizing 16S rRNA gene sequencing showed that EQR17 shared 99.4% similarity with Bacillus velezensis. Gene expression analysis further verified the presence of the quorum quenching gene aiiA, which is known to encode a lactonase enzyme accountable for degrading AHLs. Statistical analysis utilizing one-way ANOVA revealed significant reductions in biofilm formation (P<0.01), supporting the effectiveness of EQR17 as a bio control agent. Moreover, microscopy showed that untreated controls exhibited thick and layered biofilms, while the EQR17-treated groups displayed sparse, broken matrices. These findings illustrate that the Euphrates River is a source of advantageous quorum quenching bacteria and highlight Bacillus velezensis EQR17 as a promising option for developing alternative, antibiotic-free approaches for controlling bacterial infections in aquaculture systems.

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