Journal Article

Transferrin knockout reveals a tolerance phenotype against Piscirickettsia salmonis in Atlantic salmon phagocytes

Galdames-Contreras, Felipe, Jin, Yehwa, Pulgar, Rodrigo, Mejías, Madelaine, Sáez, Alejandro, Ojeda, Ingrid, Escorza, Amanda, Dettleff, Phillip, Escobar-Aguirre, Sebastián

2025

Overview

Salmonid rickettsial septicemia (SRS), caused by Piscirickettsia salmonis , is a major challenge in Chilean aquaculture. We evaluated the impact of the vaccine on fish survival, bacterial load, and iron metabolism-related gene expression under field conditions. Atlantic salmon received either a pentavalent inactivated vaccine plus a live attenuated P. salmonis vaccine (SIA) or a tetravalent control vaccine (SS). While survival was similar early (≤ 28 weeks post-seawater transfer), SIA-vaccinated fish showed greater survival by week 41 (85% vs. 52%). Quantitative PCR confirmed a reduced bacterial load in the SIA group during active infection. Expression analysis revealed distinct temporal regulation of iron metabolism genes: ferritin and hepcidin were upregulated in freshwater, whereas transferrin and its receptor were elevated in seawater in the SIA group, suggesting a link between iron homeostasis and vaccine-induced protection. To further investigate the role of transferrin, we generated transferrin-knockout (TF-KO) phagocytes using CRISPR/Cas9. In vitro infection assays revealed that, compared with wild-type (TF-WT) cells, TF-KO cells presented reduced cytopathic effects, decreased formation of P. salmonis -containing vacuoles (PCVs), and improved viability. Surprisingly, no differences in bacterial load or iron-related gene expression were detected between TF-KO and TF-WT cells, indicating that transferrin disruption did not directly alter iron homeostasis. Global transcriptomic analysis revealed 311 differentially expressed genes in TF-KO cells, with functional enrichment in metal-binding and zinc-dependent processes but no direct association with iron metabolism. These findings suggest that transferrin deficiency confers an infection-tolerant phenotype through transcriptional reprogramming unrelated to iron regulation, highlighting novel mechanisms of host‒pathogen interactions and potential avenues for SRS control in aquaculture.

• Publisher: BioMed Central,BioMed Central Ltd,Springer Nature B.V,BMC
• Subject: Adaptive immunity / Analysis / Animals / Anopheles / Antigens / aquaculture / Aquaculture industry / Bacterial Vaccines - immunology / Cell growth / CRISPR-Cas systems / Design of experiments / Development and progression / Ferritin / fish / Fish Diseases - immunology / Fish Diseases - microbiology / Fish Diseases - prevention & control / Fishes / Fresh water / freshwater / gene editing / Gene expression / Gene Knockout Techniques - veterinary / Genes / Genetic aspects / Health aspects / hepcidin / homeostasis / Immunity (Disease) / Immunology / inactivated vaccines / Infection / Infections / Infectious diseases / Iron / Iron - metabolism / iron absorption / Kidneys / Life Sciences / live vaccines / Medicine / Medicine & Public Health / Metabolism / microbial load / Microbiology / Mortality / Phagocytes - immunology / Phagocytes - microbiology / phenotype / Physiological aspects / Piscirickettsia - immunology / Piscirickettsia - physiology / Piscirickettsia salmonis / Piscirickettsiaceae Infections - immunology / Piscirickettsiaceae Infections - microbiology / Piscirickettsiaceae Infections - prevention & control / Piscirickettsiaceae Infections - veterinary / Proteins / quantitative polymerase chain reaction / Research Article / Salmo salar / Salmon / Sea-water / Seawater / septicemia / SRS / transcription (genetics) / transcriptomics / Transferrin / Transferrin - genetics / Transferrin - metabolism / Vaccination / Vaccines / Vaccines, Attenuated - immunology / Veterinary Medicine/Veterinary Science / viability / Virology