Proteome analysis of Edwardsiella ictaluri

Edwardsiella ictaluri is a facultative intracellular Gram-negative bacterium causing enteric septicemia of catfish (ESC), the most prevalent disease affecting farm-raised channel catfish in the United States. Despite its economic importance, studies addressing high-throughput proteomics were not possible because of lack of comprehensive protein database. Here, we report the first high-throughput proteomics analysis of E. ictaluri using 2-D LC ESI MS/MS and 2-DE MALDI TOF/TOF MS. Proteins identified in this study and predicted from the whole E. ictaluri genome were clustered into functional groups using clusters of orthologous groups (COG), and their subcellular locations were predicted. Possible functional relationships among proteins were determined using pathway analysis. The total number of unique E. ictaluri proteins identified using both 2-D LC and 2-DE approaches was 788, of which 15.48% (122) were identified by both methods while 78.43% (618) and 6.09% (48) were unique in 2-D LC and 2-DE, respectively. COG groupings and subcellular localizations were quite similar between our data set and proteins predicted from the whole genome. Twelve pathways were significantly represented in our dataset (p <0.05). Results from this study provided experimental evidence for many proteins that were predicted from the E. ictaluri genome annotation, and they should accelerate future functional and comparative studies aimed at understanding virulence mechanisms of this important pathogen.