Abstract
Hydrolytic extracellular enzymes degrading host tissues potentially play a role in bacterial pathogenesis. Flavobacterium psychrophilum is an important bacterial pathogen of salmonid fish reared in freshwater throughout the world. Diversity among isolates has been described at the phenotypic, serological, and genomic levels, but the links between these various traits remain poorly understood. Using a genome-wide association study, we identified a gene encoding a novel elastinolytic enzyme in F. psychrophilum To formally demonstrate enzymatic activity, this gene (FP0506 from strain JIP 02/86) was expressed in the elastinolysis-deficient strain OSU THCO2-90, resulting in proficient elastin-degrading cells. The encoded protein is predicted to be a cell-surface-exposed lipoprotein with no homology to previously reported elastases. FP0506 might belong to the zincin tribe and gluzincin clan of metalloproteases, and this new elastase-encoding gene seems to be present only in some members of the family FlavobacteriaceaeIMPORTANCE Elastin is an important proteinaceous component of vertebrate connective tissues (e.g., blood vessels, lung, and skin), to which it confers elasticity. Elastases have been identified in a number of pathogenic bacteria. They are thought to be required for tissue penetration and dissemination, acting as "spreading factors." Flavobacterium psychrophilum is a devastating bacterial pathogen of salmonid fish (salmon and trout) that is responsible for severe economic losses worldwide. This pathogen displays strong proteolytic activities. Using a variety of techniques, including genome comparisons, we identified a gene encoding a novel elastase in F. psychrophilum The encoded protein is predicted to be a cell-surface-exposed lipoprotein with no homology to previously reported elastases. In addition, this elastase likely belongs to a new family of proteases that seems to be present only in some members of this important group of bacteria.
Highlights
Hydrolytic extracellular enzymes degrading host tissues potentially play a role in bacterial pathogenesis
Flavobacterium psychrophilum, a bacterium belonging to the family Flavobacteriaceae, is a serious bacterial pathogen of salmonid fish reared in freshwater throughout the world [7, 8]
We formally demonstrated the protein function through gene expression in an elastinolysis-deficient F. psychrophilum strain, and we produced in silico evidence that the protein likely belongs to the gluzincin clan of metalloproteases (MPs), which is restricted to some members of the family Flavobacteriaceae
Summary
Hydrolytic extracellular enzymes degrading host tissues potentially play a role in bacterial pathogenesis. Flavobacterium psychrophilum is a devastating bacterial pathogen of salmonid fish (salmon and trout) that is responsible for severe economic losses worldwide. Phenotypic, serological, and genomic diversity among isolates has been described, but the links between these different areas remain largely unexplored [12,13,14,15] It remains unclear how the respective contributions of the pathogen characteristics, as opposed to the susceptibility of the fish host, affect the success and severity of the infection. No elastaseencoding gene has been characterized to date, and genome mining failed to identify a bona fide elastase gene in F. psychrophilum genomes [12, 18, 22,23,24,25]
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