“In vivo transcriptomics reveals the important role of iron acquisition systems and secreted proteins in the virulence of the fish pathogen Flavobacterium psychrophilum (6975)”

In vivo transcriptomics reveals the important role of iron acquisition systems and secreted proteins in the virulence of the fish pathogen Flavobacterium psychrophilum

Infectious diseases have a critical impact on aquaculture. Bacteria of the family Flavobacteriaceae (phylum Bacteroidota) are common in soil and aquatic environments, and several species are fish pathogens of utmost importance fish. Flavobacterium psychrophilum is responsible for bacterial cold-water disease in salmonids worldwide, with critical impact on fish farming, animal welfare, and environment due to the recurrent use of antibiotics. Despite significant insights derived from genomic studies, many genes remain uncharacterized and the molecular factors involved in the infection process, host invasion, tissues colonization and septicaemia, are mostly unknown. Previous studies have revealed the essential role of the Type IX secretion system (T9SS) in virulence, mutants of which are avirulent and exhibit pleiotropic defects. Notably, F. psychrophilum genomes contain ~ 45 genes encoding T9SS secreted proteins, including putative degradative enzymes, putative surface-exposed proteins and others of unknown function. In order to unveil genetic traits involved in virulence, we analysed bacterial adaptation to outside-host and within-host environments using a combination of in vitro and in vivo transcriptomic approaches. Among the most highly in vivo-induced genes, we identified several iron acquisition systems and genes encoding uncharacterized proteins secreted through the T9SS. Using phenotypic characterization of deletion mutants, we show that several of these genes are required for full virulence in rainbow trout. Notably, two TonB-dependent receptors acting without redundancy are required for adaptation to different conditions of iron availability encountered during infection: BfpR is upregulated in blood and is required for optimal growth in the presence of high level of hemoglobin, while HfpR with its cognate hemophore HfpY confers the capacity to acquire nutrient iron from heme or hemoglobin under iron scarcity. Other genes required for virulence are related to the respiratory chain or encode surface exposed proteins. This study provides insights into the molecular basis of pathogenicity and identify promising targets in the development of future disease control strategies.

1. ROCHAT, Tatiana, INRAE, Presenter
2. LEE, Bo-Hyung, INRAE, Author
3. GUERIN, Cyprien, INRAE, Author
4. RIGAUDEAU, Dimitri, INRAE, Author
5. NICOLAS, Pierre, INRAE, Author
6. DUCHAUD, Eric, INRAE, Author