Proteomics of rainbow trout in response to Yersinia ruckeri

Enteric red mouth (ERM) is an acute to chronic bacterial infection of fish. The disease is caused by Yersinia ruckeri, a Gram-negative rod-shaped enterobacterium. The disease leads to significant economic losses, especially in salmonids aquaculture; rainbow trout are highly susceptible to ERM. Previous studies have categorized Y. ruckeri strains into biotype 1 (motile and lipase-positive) and biotype 2 (non-motile and lipase-negative) and have identified genetic differences between the two biotypes. They have also revealed that rainbow trout show differences in mortality and immune responses. Significantly, biotype 2 strains have been responsible for outbreaks of the disease in rainbow trout that have been vaccinated (against biotype 1), thereby confirming the failure of monovalent vaccination to protect the fish against infection. There is an urgent need to understand the biochemical changes in fish and to clarify the differences in the fish immune responses to strains of biotypes 1 and 2. Proteomics can provide significant information on biochemical changes in tissues and cells. To date, there is a paucity of knowledge of the actual host proteins whose expression is up-or down-regulated during infection with Y. ruckeri. This project main aims to identify differentially expressed protein profiles of rainbow trout infected with Y. ruckeri biotype 1 and biotype 2 at different time points, to elucidate the proteomic background for the observed biochemical changes and to analyse the mechanism of action of the proteins whose expression differs after infection by the two strains. After experimental infection of rainbow trout with Y. ruckeri biotype 1 and biotype 2, samples of different organs will be collected at different time points. Proteomic approaches will be used to identify differentially expressed proteins in fish tissues. Differentially expressed protein levels will be confirmed by Western blotting. Biological functions and networks of the proteins will be investigated. This study will give rise to the first proteomic profiles on the protein mechanisms of rainbow trout in response to bacterial infection. The project will help to explain the observed expressed protein differences in rainbow trout in response to biotype 1 and biotype 2 infections. The identified proteins will be analysed to provide dynamic information to help us understand the biological processes and biochemical pathways activated by infection, such as signal transduction and proteasome activity. In future, the identified proteins will be used to develop markers or protein chip approaches for the identification of disease-resistant fish and in therapeutic approaches to knock down genes implicated in disease.

Yersinia ruckeri is the causative agent of enteric redmouth disease in salmonids worldwide. It has a wide host range, broad geographical distribution, and causes significant economic losses in the fish aquaculture industry. Clinical signs of disease include subcutaneous hemorrhages, exophthalmia, splenomegaly and inflammation of the lower intestine. Y. ruckeri strains are classified into biotype 1 and biotype 2 strains. Rainbow trout are fast growing and robust under farming conditions, and thus are the most widely farmed salmonid fish. Rainbow trout are especially susceptible to both biotype 1 and biotype 2 Y. ruckeri strains. We were interested in identifying proteome alteration in organs of rainbow trout during the infection process of Y. ruckeri strains. For this study, rainbow trout were experimentally infected by Y. ruckeri strains. Organs: head kidney, spleen and lower intestine were sampled at different time points. Samples of individual organs were analyzed with a shotgun proteomic approach. Protein functions and protein-protein interaction were predicted using bioinformatic tools. Results of this project demonstrated that Y. ruckeri modulates the expression of a wide range of head kidney, spleen and lower intestine proteins with a various functions. Some immune- related proteins such as lysozyme C, thioredoxin, chemotaxin, precerebellin-like protein, cathepsin B, C type lectin B and tetraspanin were strongly up-regulated in infected rainbow trout. The findings of this study regarding the immune response at the protein level offer new insight into the systemic response to Y. ruckeri strains in rainbow trout. Biotype 1 and biotype 2 Y. ruckeri strains induce minor proteomic changes in the organs of rainbow trout. Predicted carbon metabolism, ribosome and phagosome pathways might be useful in understanding biological processes and further pioneering research work on proteomics. The identified proteome profiles will serve as a template for understanding organ functions in salmonids and will increase the amount of spectra information of rainbow trout proteins in the public proteomics data repository.