535
et al. 1990 ) acts as a positive regulator of anguibactin biosynthesis and the transcription of the iron-transport genes FatA and FatB (Actis et al. 1995 ; Chen et al. 1996 ).
Also, V. anguillarum has a plasmid-encoded histamine decarboxylase gene angH,
which is essential for the biosynthesis of anguibactin (Barancin et al. 1998 ). The
overall effect is that the system enables the bacterial cell to compete for available
iron in the fi sh tissues. Two OMP have been designated as OM2 (molecular
weight = 86 kDa) and OM3 (molecular weight = 79 kDa). The siderophore and OM2
are coded by plasmid pJM1, whereas OM3 is a function of chromosomal involvement. The basic mechanism involves diffusion of the siderophore into the environment, and the formation of iron complexes that attach to OM2, presumably leading
to transport of the iron into the bacterial cell (Crosa and Hodges 1981 ; Crosa et al.
1983 ; Tolmasky and Crosa 1984 ; Actis et al. 1985 ; Mackie and Birkbeck 1992 ).
Thus, invading bacteria may multiply in the host by scavenging successfully for the
iron that is bound by high-affi nity iron-binding proteins, such as transferrin, lactoferrin and ferritin. These are present in the serum, secretions and tissues, respectively (Bullen et al. 1978 ). Toranzo et al. ( 1983a , b ) complicated the issue by
publishing data that showed that virulent strains, obtained from striped bass, did not
contain plasmids. Yet, all the isolates grew in iron-limiting conditions, during which
new OMP and a siderophore were found. Chromosomal DNA sequences, which
hybridised with pJM1, were present. Thus, it seems likely that the plasmid DNA
had become integrated into the bacterial chromosome.
A pJM1-like plasmid, pEIB1, has been sequenced, and determined to comprise
66,164 bp encoding 44 ORFs (>400 bp) containing genes for biosynthesis and regulation of anguibactin, transport of ferric-anguibactin complexes and DNA replication (Wu et al. 2004 ).
Work proved that a separate iron-uptake system was contained on the chromosome. This differed from the plasmid-mediated system, insofar as the diffusible
siderophore is not utilised as an external siderophore, and different OMP are synthesised (Lemos et al. 1988 ; Conchas et al. 1991 ; Mackie and Birkbeck 1992 ).
Siderophores of the phenolate class, possibly related to enterobactin, have been
found in New Zealand isolates (Pybus et al. 1994 ). Interestingly, iron-uptake mechanisms have been reported in non-pathogenic cultures (Lemos et al. 1991 ), casting
some doubt on the precise relevance of the mechanism to pathogenicity.
A catechol-type siderophore, termed vanchrobactin, has been reported in some
strains (e.g. Balado et al. 2008 ). The genes, vabA, vabB, vabE, vabF, vabG (encodes
a 3-deoxy-D-arabino-heptulosonate-7-phosphate synthetase) , vabS, vabH, vabR
(encodes a Lys-R-family transcriptional regulator) and fvtA (a putative siderophore
receptor) have been identifi ed. Deletion of vabG or vabD led to a reduction in
growth in iron-limitation. A vabD mutant did not produce any vanchrobactin; a vab
mutant demonstrated the ability for residual production. By PCR, it was deduced
that the gene cluster is arranged into 6 iron-regulated transcriptional units, with ferric uptake regulator protein (Fur) as the principle ion-responsive regulator of the
genes (Balado et al. 2008 ).
But what about the other serogroups? The virulence plasmid, pJM1, has not been
found in representatives of any other serogroup (Austin et al. 1995a ). Yet, we regard
Vibrio anguillarum
et al. 1990 ) acts as a positive regulator of anguibactin biosynthesis and the transcription of the iron-transport genes FatA and FatB (Actis et al. 1995 ; Chen et al. 1996 ).
Also, V. anguillarum has a plasmid-encoded histamine decarboxylase gene angH,
which is essential for the biosynthesis of anguibactin (Barancin et al. 1998 ). The
overall effect is that the system enables the bacterial cell to compete for available
iron in the fi sh tissues. Two OMP have been designated as OM2 (molecular
weight = 86 kDa) and OM3 (molecular weight = 79 kDa). The siderophore and OM2
are coded by plasmid pJM1, whereas OM3 is a function of chromosomal involvement. The basic mechanism involves diffusion of the siderophore into the environment, and the formation of iron complexes that attach to OM2, presumably leading
to transport of the iron into the bacterial cell (Crosa and Hodges 1981 ; Crosa et al.
1983 ; Tolmasky and Crosa 1984 ; Actis et al. 1985 ; Mackie and Birkbeck 1992 ).
Thus, invading bacteria may multiply in the host by scavenging successfully for the
iron that is bound by high-affi nity iron-binding proteins, such as transferrin, lactoferrin and ferritin. These are present in the serum, secretions and tissues, respectively (Bullen et al. 1978 ). Toranzo et al. ( 1983a , b ) complicated the issue by
publishing data that showed that virulent strains, obtained from striped bass, did not
contain plasmids. Yet, all the isolates grew in iron-limiting conditions, during which
new OMP and a siderophore were found. Chromosomal DNA sequences, which
hybridised with pJM1, were present. Thus, it seems likely that the plasmid DNA
had become integrated into the bacterial chromosome.
A pJM1-like plasmid, pEIB1, has been sequenced, and determined to comprise
66,164 bp encoding 44 ORFs (>400 bp) containing genes for biosynthesis and regulation of anguibactin, transport of ferric-anguibactin complexes and DNA replication (Wu et al. 2004 ).
Work proved that a separate iron-uptake system was contained on the chromosome. This differed from the plasmid-mediated system, insofar as the diffusible
siderophore is not utilised as an external siderophore, and different OMP are synthesised (Lemos et al. 1988 ; Conchas et al. 1991 ; Mackie and Birkbeck 1992 ).
Siderophores of the phenolate class, possibly related to enterobactin, have been
found in New Zealand isolates (Pybus et al. 1994 ). Interestingly, iron-uptake mechanisms have been reported in non-pathogenic cultures (Lemos et al. 1991 ), casting
some doubt on the precise relevance of the mechanism to pathogenicity.
A catechol-type siderophore, termed vanchrobactin, has been reported in some
strains (e.g. Balado et al. 2008 ). The genes, vabA, vabB, vabE, vabF, vabG (encodes
a 3-deoxy-D-arabino-heptulosonate-7-phosphate synthetase) , vabS, vabH, vabR
(encodes a Lys-R-family transcriptional regulator) and fvtA (a putative siderophore
receptor) have been identifi ed. Deletion of vabG or vabD led to a reduction in
growth in iron-limitation. A vabD mutant did not produce any vanchrobactin; a vab
mutant demonstrated the ability for residual production. By PCR, it was deduced
that the gene cluster is arranged into 6 iron-regulated transcriptional units, with ferric uptake regulator protein (Fur) as the principle ion-responsive regulator of the
genes (Balado et al. 2008 ).
But what about the other serogroups? The virulence plasmid, pJM1, has not been
found in representatives of any other serogroup (Austin et al. 1995a ). Yet, we regard
Vibrio anguillarum