The AsaP1 Peptidase of Aeromonas salmonicida subsp. achromogenes Is a Highly Conserved Deuterolysin Metalloprotease (Family M35) and a Major Virulence Factor

Abstract

ABSTRACT Infections by the bacterium Aeromonas salmonicida subsp. achromogenes cause significant disease in a number of fish species. In this study, we showed that AsaP1, a toxic 19-kDa metallopeptidase produced by A. salmonicida subsp. achromogenes , belongs to the group of extracellular peptidases ( Aeromonas type) (MEROPS ID M35.003) of the deuterolysin family of zinc-dependent aspzincin endopeptidases. The structural gene of AsaP1 was sequenced and found to be highly conserved among gram-negative bacteria. An isogenic Δ asaP1 A. salmonicida subsp. achromogenes strain was constructed, and its ability to infect fish was compared with that of the wild-type (wt) strain. The Δ asaP1 strain was found to infect Arctic charr, Atlantic salmon, and Atlantic cod, but its virulence was decreased relative to that of the wt strain. The 50% lethal dose of the AsaP1 mutant was 10-fold higher in charr and 5-fold higher in salmon than that of the wt strain. The pathology induced by the AsaP1-deficient strain was also different from that of the wt strain. Furthermore, the mutant established significant bacterial colonization in all observed organs without any signs of a host response in the infected tissue. AsaP1 is therefore the first member of the M35 family that has been shown to be a bacterial virulence factor.