Tad pili contribute to the virulence and biofilm formation of virulent Aeromonas hydrophila

Authors: TEKEDAR, HASAN - Mississippi State University; PATEL, FENNY - Mississippi State University; BLOM, JOCHEN - Justus-Liebig University; GRIFFIN, MATT - Mississippi State University; Waldbieser, Geoffrey; KUMRU, SALIH - Recep Tayyip Erdogan University; ABDELHAMED, HOSSAM - Mississippi State University; DHARAN, VANDANA - Mississippi State University; HANSON, LARRY - Mississippi State University; LAWRENCE, MARK - Mississippi State University

Submitted to: Frontiers in Cellular and Infection Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2024
Publication Date: 7/31/2024
Citation: Tekedar, H.C., Patel, F., Blom, J., Griffin, M.J., Waldbieser, G.C., Kumru, S., Abdelhamed, H., Dharan, V., Hanson, L.A., Lawrence, M.A. 2024. Tad pili contribute to the virulence and biofilm formation of virulent Aeromonas hydrophila. Frontiers in Cellular and Infection Microbiology. https://doi.org/10.3389/fcimb.2024.1425624.
DOI: https://doi.org/10.3389/fcimb.2024.1425624

Interpretive Summary: Infections of virulent Aeromonas hydrophila bacteria can cause significant "losses in commercial catfish culture and have been implicated" in drastic mortality events in growing catfish. Researchers at the USDA, ARS, Warmwater Aquaculture Research Unit and Mississippi State University investigated the role of the A. hydrophila pilus as a potential virulence factor. Pili are long extracellular polymers that enable the bacteria to interact with their environment to adhere, form biofilms, or provide motility. Genomic comparisons of pilus genes in epidemic isolates of A. hydrophila revealed a unique genetic locus called the Tad operon. Targeted experimental disruption showed that complete knockout of the Tad operon significantly reduced A. hydrophila's pathogenicity in catfish fingerlings. This research showed the Tad locus has a potential role in A. hydrophila pathogenicity, and could be a target for vaccine development.

Technical Abstract: Type IV pili (T4P), are versatile proteinaceous protrusions that mediate diverse cellular processes, including adhesion, motility, and biofilm formation. Aeromonas hydrophila, a versatile gram-negative facultative anaerobe posing threat to a wide range of hosts leading to chronic infections. Previously, we reported presence of a unique Type IV class C pilus, known as tight adherence (Tad), in epidemic and clinical isolates of Aeromonas hydrophila. In the present study, we sought to functionalize the role of Tad operon in the pathogenicity of A. hydrophila ML09-119. Through comprehensive comparative genomics analysis of 170 A. hydrophila genomes, we confirmed the conserved presence of the Tad operon in epidemic fish and clinical isolates, suggesting its potential contribution to pathogenicity. First, we identified that A. hydrophila ML09-119 encodes 13 Tad operon genes. We conducted targeted knockout of this operon to elucidate its specific role in A. hydrophila virulence. Our findings demonstrate that a complete knockout of the Tad operon is required for a significant reduction in pathogenicity in catfish fingerlings, highlighting its essential role in mediating host-pathogen interactions during infection. Biofilm formation of A. hydrophila ML09-119 was significantly affected by complete deletion of Tad operon. Furthermore, we characterized the EAh'tad via various assays, including pH, hydrogen peroxide, osmolar, alkaline, and temperature stress. Additionally, we observed structural changes under SEM (Scanning electron microscopy), unveiling distinct characteristics in actively dividing A. hydrophila cells. These findings will enhance our understanding of the pathogenic role of the Tad cluster in A. hydrophila with broader implications for unraveling mechanisms driven by T4P to combat bacterial infections.