Proteomic analysis of Flavobacterium psychrophilum cultured in vivo and in iron-limited media.

Flavobacterium psychrophilum is the etiologic agent of bacterial coldwater disease, but the pathogenic mechanisms of this important fish pathogen are not fully understood. Identifying bacterial genes of F. psychrophilum differentially expressed in vivo may lead to a better understanding of pathogenesis and provide targets for vaccine development. Therefore, the present study used a proteomic approach to identify and quantify proteins of F. psychrophilum following growth in vivo and under iron-limited growth conditions. As determined by 2D polyacrylamide gel electrophoresis (2D-PAGE), numerous proteins exhibited different spot intensities following culture of the bacterium in vivo, and of these, 20 were selected and identified by liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) analysis and Mascot searches of the F. psychrophilum genome. Eighteen proteins exhibited increased spot intensities in vivo, and these included: several chaperone and stress proteins, gliding motility protein GldN, outer membrane protein OmpH, 2 probable outer membrane proteins (OmpA family), probable aminopeptidase precursor, probable lipoprotein precursor, 3-oxoacyl-[acyl-carrier-protein]-reductase, and several proteins with unknown function. Two proteins exhibited decreased spot intensities in vivo and were identified as ferritin FtnA and outer membrane protein OmpA (P60). Culture of F. psychrophilum in iron-limited media resulted in similar protein spot intensity changes for 6 of the 20 proteins identified following growth in vivo. Results from the present study suggest a role of upregulated proteins in the pathogenesis of F. psychrophilum and these may represent potential vaccine candidate antigens.