Characterization of Type VI secretion system in Edwardsiella ictaluri

Safak Kalindamar; Hossam Abdelhamed; Adef O Kordon; Hasan C Tekedar; Lesya Pinchuk; Attila Karsi

doi:10.1371/journal.pone.0296132

Characterization of Type VI secretion system in Edwardsiella ictaluri

PLoS One. 2023 Dec 28;18(12):e0296132. doi: 10.1371/journal.pone.0296132. eCollection 2023.

Authors

Safak Kalindamar¹, Hossam Abdelhamed², Adef O Kordon², Hasan C Tekedar², Lesya Pinchuk², Attila Karsi²

Affiliations

¹ Department of Molecular Biology and Genetics, Faculty of Arts and Sciences, Ordu University, Ordu, Türkiye.
² Department of Comparative Biomedical Sciences, College of Veterinary Medicine, Mississippi State University, Mississippi State, MS, United States of America.

Abstract

Edwardsiella ictaluri is a Gram-negative facultative intracellular fish pathogen causing enteric septicemia of catfish (ESC). While various secretion systems contribute to E. ictaluri virulence, the Type VI secretion system (T6SS) remains poorly understood. In this study, we constructed 13 E. ictaluri T6SS mutants using splicing by overlap extension PCR and characterized them, assessing their uptake and survival in channel catfish (Ictalurus punctatus) peritoneal macrophages, attachment and invasion in channel catfish ovary (CCO) cells, in vitro stress resistance, and virulence and efficacy in channel catfish. Among the mutants, EiΔevpA, EiΔevpH, EiΔevpM, EiΔevpN, and EiΔevpO exhibited reduced replication inside peritoneal macrophages. EiΔevpM, EiΔevpN, and EiΔevpO showed significantly decreased attachment to CCO cells, while EiΔevpN and EiΔevpO also displayed reduced invasion of CCO cells (p < 0.05). Overall, T6SS mutants demonstrated enhanced resistance to oxidative and nitrosative stress in the nutrient-rich medium compared to the minimal medium. However, EiΔevpA, EiΔevpH, EiΔevpM, EiΔevpN, and EiΔevpO were susceptible to oxidative stress in both nutrient-rich and minimal medium. In fish challenges, EiΔevpD, EiΔevpE, EiΔevpG, EiΔevpJ, and EiΔevpK exhibited attenuation and provided effective protection against E. ictaluri wild-type (EiWT) infection in catfish fingerlings. However, their attenuation and protective efficacy were lower in catfish fry. These findings shed light on the role of the T6SS in E. ictaluri pathogenesis, highlighting its significance in intracellular survival, host cell attachment and invasion, stress resistance, and virulence. The attenuated T6SS mutants hold promise as potential candidates for protective immunization strategies in catfish fingerlings.

Copyright: © 2023 Kalindamar et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

MeSH terms

Animals
Catfishes*
Edwardsiella ictaluri / genetics
Enterobacteriaceae Infections*
Fish Diseases* / prevention & control
Ictaluridae*
Type VI Secretion Systems* / genetics
Virulence

Substances

Type VI Secretion Systems

Grants and funding

This project was supported by Agriculture and Food Research Initiative competitive grant no. 2016-67015-24909 from the USDA National Institute of Food and Agriculture. Bioluminescence imaging was supported by USDA-ARS Biophotonics Initiative #58-6402-3-018. Safak Kalindamar was supported by a fellowship from the Ministry of National Education of Turkey. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.