In order to identify genes encoding the outer
membrane proteins (OMPs) of the myxobacter Flavobacterium columnare G(4), the expression library of the bacterium was screened by using rabbit
antisera developed against its OMPs. Positive colonies of Escherichia coli
M15 containing fragments encoding the bacterial OMPs were selected for cloning the relevant genes by genomic walking methods. Two genes encoding a membrane-associated
zinc metalloprotease and
prolyl oligopeptidase are reported in this paper. The membrane-associated
zinc metalloprotease gene (map) is 1800 bp in length, coding for 449
amino acids (aa). Despite the presence of a conserved motif HEXXH for all
metalloproteases, the special HEXXH approximately 32 aa approximately E motif of the F. columnare G(4) Map and its low level of identity with other reported
zinc-containing
metalloproteases may imply that the membrane-associated
zinc metalloprotease of F. columnare G(4) represents a new family of zincins. The gene encoding
prolyl oligopeptidase (Pop), a
serine proteinase, is 2352 bp in length, coding for 649 aa. Sequence homology analysis revealed that the Pop is also novel as it has < 50% identity with other reported
prolyl oligopeptidase family
proteins. The present study represents the first to employ anti-fish bacterial OMP sera to screen genes of membrane-associated
proteases of fish pathogenic bacteria, and to provide necessary information for the examination of the role of the two genes in the
infection and pathogenesis of F. columnare.