273
Proteases, as prime candidates for exerting a signifi cant role in disease pathogenesis, have aroused substantial interest as a research topic. Indeed, a variety of investigators have performed detailed analyses, and suggested heterogeneity among
isolates. In particular, Gudmundsdóttir ( 1996 ) described 6 protease groups, but this
information might have greater value for taxonomy than an understanding of pathogenicity. Thus by examining 5 typical and 25 atypical isolates, it was determined
that the proteases produced by the type strains of Aer. salmonicida subsp. achromogenes (this produced a metalloendopeptidase = AsaP1; Schwenteit et al. 2015 ) and
Aer. salmonicida subsp. salmonicida were different to those of the fresh isolates.
Moreover, all the typical isolates belonged to one protease group with proteolytic
activities comparable to P1 and P2 proteases, whereas the atypical cultures were
different. With the exception of three atypical oxidase-negative isolates, which
secreted a protease reminiscent of P1, the others produced metallo-gelatinase. Ten
of the atypical isolates produced AsaP1 (Gudmundsdóttir 1996 ).
Shieh and MacLean ( 1975 ) purifi ed a proteolytic enzyme, which was determined
to have a molecular weight of 11 kDa, and an optimum pH range of 8–11. Because
the enzyme was inhibited by PMSF, these workers concluded that it was a serine
protease. Mellergaard ( 1983 ) also isolated and purifi ed a proteolytic enzyme
(molecular weight = 87.5 kDa; optimum pH of 9.0), as did Tajima et al. ( 1984 ), who
reported the presence of an extracellular protease with a molecular weight of
71 kDa, and a pH range of 5–10. This enzyme was deduced to be an alkaline serine
protease. Sheeran et al. ( 1984 ) described two extracellular proteolytic activities that
differed in their susceptibility to inhibitors and substrate specifi city. One of the
enzymes, designated P1, hydrolysed casein, elastin and gelatin, and showed a low
non-specifi c activity against collagen. The second enzyme (P2) hydrolysed collagen
and gelatin, but not casein or elastin; a pattern that suggested it is a specifi c collagenase. Also, Rockey et al. ( 1988 ) described two proteases, coined P1 and P2, and a
haemolysin (T-lysin) in the ECP. P1 and T-lysin were shown to work separately in
the complete lysis of (rainbow trout) erythrocytes. T-lysin interacted with the outer
membrane of the erythrocytes, whereas P1 destroyed the nuclear membrane. A role
for P2 was not described. Hastings and Ellis ( 1985 ) recorded differences in the pattern of extracellular protein production, according to the origin of the bacterial isolates. For example, isolates from Iceland (achromogenic) and the USA lacked
caseinase and gelatinase activity in the ECP. Indeed, an isolate of Aer. salmonicida
subsp. achromogenes from Iceland has been credited with the production of a novel
metallo-protease (Gudmundsdóttir et al. 1990 ). For other strains, caseinase and
gelatinase activities were inhibited by PMSF and EDTA. These data suggested that
both enzyme activities could be attributed to a single serine protease, which depends
upon divalent cations for activity. An extracellular metallo-caseinase, AsaP1, has
been linked with lethal toxicity of atypical Aer. salmonicida in Atlantic salmon,
with furuncles being produced by ECP with AsaP1 (Gunnlaugsdóttir and
Gudmundsdóttir 1997 ).
Using the “P1” and “P2” terminology, Lygren et al. ( 1998 ) discussed differences
in protease secretion according to the age of the culture of Aer. salmonicida subsp.
salmonicida. Essentially, two different proteolytic activities were found in early and
Aeromonas salmonicida
Proteases, as prime candidates for exerting a signifi cant role in disease pathogenesis, have aroused substantial interest as a research topic. Indeed, a variety of investigators have performed detailed analyses, and suggested heterogeneity among
isolates. In particular, Gudmundsdóttir ( 1996 ) described 6 protease groups, but this
information might have greater value for taxonomy than an understanding of pathogenicity. Thus by examining 5 typical and 25 atypical isolates, it was determined
that the proteases produced by the type strains of Aer. salmonicida subsp. achromogenes (this produced a metalloendopeptidase = AsaP1; Schwenteit et al. 2015 ) and
Aer. salmonicida subsp. salmonicida were different to those of the fresh isolates.
Moreover, all the typical isolates belonged to one protease group with proteolytic
activities comparable to P1 and P2 proteases, whereas the atypical cultures were
different. With the exception of three atypical oxidase-negative isolates, which
secreted a protease reminiscent of P1, the others produced metallo-gelatinase. Ten
of the atypical isolates produced AsaP1 (Gudmundsdóttir 1996 ).
Shieh and MacLean ( 1975 ) purifi ed a proteolytic enzyme, which was determined
to have a molecular weight of 11 kDa, and an optimum pH range of 8–11. Because
the enzyme was inhibited by PMSF, these workers concluded that it was a serine
protease. Mellergaard ( 1983 ) also isolated and purifi ed a proteolytic enzyme
(molecular weight = 87.5 kDa; optimum pH of 9.0), as did Tajima et al. ( 1984 ), who
reported the presence of an extracellular protease with a molecular weight of
71 kDa, and a pH range of 5–10. This enzyme was deduced to be an alkaline serine
protease. Sheeran et al. ( 1984 ) described two extracellular proteolytic activities that
differed in their susceptibility to inhibitors and substrate specifi city. One of the
enzymes, designated P1, hydrolysed casein, elastin and gelatin, and showed a low
non-specifi c activity against collagen. The second enzyme (P2) hydrolysed collagen
and gelatin, but not casein or elastin; a pattern that suggested it is a specifi c collagenase. Also, Rockey et al. ( 1988 ) described two proteases, coined P1 and P2, and a
haemolysin (T-lysin) in the ECP. P1 and T-lysin were shown to work separately in
the complete lysis of (rainbow trout) erythrocytes. T-lysin interacted with the outer
membrane of the erythrocytes, whereas P1 destroyed the nuclear membrane. A role
for P2 was not described. Hastings and Ellis ( 1985 ) recorded differences in the pattern of extracellular protein production, according to the origin of the bacterial isolates. For example, isolates from Iceland (achromogenic) and the USA lacked
caseinase and gelatinase activity in the ECP. Indeed, an isolate of Aer. salmonicida
subsp. achromogenes from Iceland has been credited with the production of a novel
metallo-protease (Gudmundsdóttir et al. 1990 ). For other strains, caseinase and
gelatinase activities were inhibited by PMSF and EDTA. These data suggested that
both enzyme activities could be attributed to a single serine protease, which depends
upon divalent cations for activity. An extracellular metallo-caseinase, AsaP1, has
been linked with lethal toxicity of atypical Aer. salmonicida in Atlantic salmon,
with furuncles being produced by ECP with AsaP1 (Gunnlaugsdóttir and
Gudmundsdóttir 1997 ).
Using the “P1” and “P2” terminology, Lygren et al. ( 1998 ) discussed differences
in protease secretion according to the age of the culture of Aer. salmonicida subsp.
salmonicida. Essentially, two different proteolytic activities were found in early and
Aeromonas salmonicida