Abstract
BackgroundVibriosis caused by V. anguillarum is a commonly encountered disease in Atlantic cod farms and several studies indicate that the initiation of infection occurs after the attachment of the pathogen to the mucosal surfaces (gut, skin and gills) of fish. Therefore it is necessary to investigate the role of different mucosal components in fish upon V. anguillarum infection. The present study has two parts; in the first part we analyzed the differential expression of skin mucus proteins from Atlantic cod naturally infected with V. anguillarum using two dimensional gel electrophoresis coupled with mass spectrometry. In the second part, a separate bath challenge experiment with V. anguillarum was conducted to assess the mRNA levels of the genes in skin tissue, corresponding to the selected proteins identified in the first part.ResultsComparative proteome analysis of skin mucus of cod upon natural infection with V. anguillarum revealed key immune relevant proteins like calpain small subunit 1, glutathione-S-transferase omega 1, proteasome 26S subunit, 14-kDa apolipoprotein, beta 2-tubulin, cold inducible RNA binding protein, malate dehydrogenase 2 (mitochondrial) and type II keratin that exhibited significant differential expression. Additionally a number of protein spots which showed large variability amongst individual fish were also identified. Some of the proteins identified were mapped to the immunologically relevant JNK (c-Jun N-terminal kinases) signalling pathway that is connected to cellular events associated with pathogenesis. A bath challenge experiment with V. anguillarum showed differential expression of beta 2-tubulin, calpain small subunit 1, cold inducible RNA binding protein, flotillin1, and glutathione S-transferase omega 1 transcripts in the skin tissue of cod during early stages of infection.ConclusionsDifferentially expressed proteins identified in the cod skin mucus point towards their possible involvement in V. anguillarum pathogenesis. The role of some of these proteins in vibriosis in cod described in this paper can be considered unconventional with respect to their established functions in higher vertebrates. Based on the differential expression of these proteins they are possibly important components of fish defence against bacteria and innate immunity at large. The feasibility of utilizing these proteins/genes as markers of bacterial infection or stress in cod needs to be explored further.
Highlights
Vibriosis caused by V. anguillarum is a commonly encountered disease in Atlantic cod farms and several studies indicate that the initiation of infection occurs after the attachment of the pathogen to the mucosal surfaces of fish
V. anguillarum infected Atlantic cod juveniles Atlantic cod juveniles hatched at Mørkvedbukta Research Station, University of Nordland, Bodø, Norway in early spring 2011 had a natural outbreak of vibriosis during late summer 2011
A recent report on the expression of key immune relevant genes in naive Atlantic cod skin [57] taken together with the present study demonstrates the role of immune relevant components in the skin mucus/skin of cod both at protein and transcript level during bacterial infection
Summary
Vibriosis caused by V. anguillarum is a commonly encountered disease in Atlantic cod farms and several studies indicate that the initiation of infection occurs after the attachment of the pathogen to the mucosal surfaces (gut, skin and gills) of fish. Vibrio anguillarum strains O2α and O2β are commonly associated with vibriosis in cod [4,5] and these infections can cause bleeding skin lesions/ulcers and septicemia, resulting in mass mortalities of farmed cod [6]. Vibrio infection in mammals is initiated at gut mucosal surfaces [9] This information spurred investigations on the role of mucosal surfaces in fish, especially in the gut during the progress of vibriosis. Mucosal antibody production has been quantified upon V. anguillarum infection [15] These findings indicate that the pathogen invasion can trigger immune responses in skin and its associated mucosal surface
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