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Applied and Environmental Microbiology, September 2005, p. 5107-5115, Vol. 71, No. 9
0099-2240/05/$08.00+0 doi:10.1128/AEM.71.9.5107-5115.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
Phylogeny and Molecular Identification of Vibrios on the Basis of Multilocus Sequence Analysis
F. L. Thompson,1*
D. Gevers,2
C. C. Thompson,1
P. Dawyndt,2
S. Naser,2
B. Hoste,2
C. B. Munn,3 and
J. Swings2
Microbial Resources Division and Brazilian Collection of Environmental and Industrial Micro-Organisms (CBMAI), CPQBA, UNICAMP, CP 6171, 13081-970 Campinas, Brazil,1
Laboratory of Microbiology and BCCM/LMG Bacteria Collection, Ghent University, K. L. Ledeganckstraat 35, Ghent 9000, Belgium,2
School of Biological Sciences, University of Plymouth, B417, Portland Square, Drake Circus, Plymouth, Devon PL4 8AA, United Kingdom3
Received 9 August 2004/
Accepted 3 April 2005

ABSTRACT
We analyzed the usefulness of
rpoA,
recA, and
pyrH gene sequences
for the identification of vibrios. We
sequenced fragments of
these loci from a collection of 208
representative strains,
including 192 well-documented
Vibrionaceae strains and 16 presumptive
Vibrio
isolates associated with coral bleaching. In order to
determine the
intraspecies variation among the three loci, we
included several
representative strains per species. The phylogenetic
trees constructed
with the different genetic loci were roughly
in agreement with former
polyphasic taxonomic studies, including
the 16S rRNA-based phylogeny of
vibrios. The families
Vibrionaceae,
Photobacteriaceae,
Enterovibrionaceae, and
Salinivibrionaceae were all differentiated
on the basis of
each genetic locus. Each species clearly formed
separated clusters with
at least 98, 94, and 94%
rpoA,
recA,
and
pyrH gene sequence similarity, respectively. The genus
Vibrio was heterogeneous and polyphyletic, with
Vibrio
fischeri,
V. logei, and
V. wodanis grouping
closer to the
Photobacterium genus.
V. halioticoli-,
V. harveyi-,
V. splendidus-, and
V.
tubiashii-related
species formed groups within the genus
Vibrio. Overall, the
three genetic loci were more
discriminatory among species than
were 16S rRNA sequences. In some
cases, e.g., within the
V. splendidus and
V.
tubiashii group,
rpoA gene sequences were
slightly less
discriminatory than
recA and
pyrH sequences. In
these
cases, the combination of several loci will yield the
most robust
identification. We can conclude that strains of
the same species will
have at least 98, 94, and 94%
rpoA,
recA,
and
pyrH gene sequence similarity,
respectively.

INTRODUCTION
Vibrios are gram-negative, usually motile rods, are mesophilic
and
chemoorganotrophic, and have a facultatively fermentative
metabolism
(
5). They are
generally able to grow on marine agar and on the
selective medium
thiosulfate-citrate-bile salt-sucrose agar
and are mostly oxidase
positive. Vibrios belong to the
Gammaproteobacteria according
to 16S rRNA gene sequence analysis. These bacteria
are found abundantly
in aquatic habitats and in association
with eukaryotes. Associations
established by vibrios range from
mutualistic, e.g.,
Vibrio
fischeri-bobtail squid
(
26), to pathogenic,
e.g.,
V. cholerae-humans
(
45). Probiotic
Vibrio strains for fish and
shellfish have also been
documented
(
44).
The current
family Vibrionaceae comprises the genera Enterovibrio
(2 species), Grimontia (1 species), Photobacterium (7
species), Salinivibrio (1 species), and Vibrio (64
species). The novel species Photobacterium rosenbergii and
Enterovibrio coralii have recently been proposed to encompass
isolates associated with coral bleaching
(41). Several new
Vibrio species, mainly in the phylogenetic neighborhood of
V. harveyi, V. halioticoli, V. splendidus,
V. tubiashii, and V. fluvialis, have been described
in the last few years, with V. neonatus, V. ezurae
(28), and V.
ponticus (22) being
the most recent ones. V. harveyi, V. splendidus, and
V. tubiashii are frequently associated with disease in
different species of fish and shellfish worldwide, while the V.
halioticoli group comprises species that are potentially mutualist
to abalones (28). These
organisms may be promising probionts for abalone
rearing.
Accurate identification of vibrios at the family and
genus levels is obtained by 16S rRNA gene sequencing, whereas
identification at the species and strain levels requires the
application of genomic analyses, including DNA-DNA hybridization,
repetitive extragenic palindromic PCR, and amplified
fragment length polymorphism (AFLP) analysis
(40). These techniques
are essential for reliable species identification, because several
vibrios have nearly identical 16S rRNA sequences and similar phenotypic
features (10).
Unfortunately, their use is restricted to a few reference laboratories.
Interlaboratory comparisons of fingerprint patterns are difficult. The
sequencing of housekeeping genes is emerging as an alternative to
overcome this problem. In addition, this type of data may improve the
current pragmatic definition of bacterial species
(28a). In silico
whole-genome analysis applied to the Gammaproteobacteria
identified a set of 203 genes that are most valuable for inferring
bacterial phylogeny
(18a). According to
Gevers et al. (8), 135 of
these genes are not conserved outside the Gammaproteobacteria
and thus may not be appropriate for phylogenetic studies on a broader
taxonomic scale.
Different loci, e.g., 23S rRNA
(21), gapA
(23), gyrB
(20), hsp60
(18), and recA
(30), have been used for
phylogenetic studies and the identification of Vibrionaceae
species. So far, these genes (except for recA) have only been
examined in a very limited number of species and strains. Thompson et
al. (30) analyzed the
recA sequences of most vibrios, but mainly using type strains,
making it difficult to draw conclusions about the use of this gene as
an identification marker. Alternative phylogenetic markers should
fulfill several criteria, as put forward by Zeigler
(46): (i) the genes must
be widely distributed among genomes, (ii) the genes must be present as
a single copy within a given genome, (iii) the individual gene
sequences must be long enough to contain sufficient information but
short enough to allow sequencing in a convenient way (900 to 2,250
nucleotides [nt]), and (iv) the sequences must predict whole-genome
relationships with acceptable precision and accuracy that correlate
well with the 16S rRNA data and with whole-genome similarities measured
by, e.g., DNA-DNA hybridization. A combination of in silico analyses
and recent experimental studies of different bacteria,
including Bacillus, Proteobacteria, lactic
acid bacteria, Mycobacterium, and Mycoplasma,
suggested that the RNA polymerase alpha subunit gene (rpoA),
recA, and the uridylate kinase gene (pyrH) fulfill
these requisites and could therefore be used for identification
purposes (8,
18a,
46).
For the
present study, we analyzed the rpoA, recA, and
pyrH gene sequences of 192 well-documented
Vibrionaceae strains comprising all currently known species
(except for Photobacterium profundum, V. agarivorans,
V. calviensis, V. ruber, V. ponticus, and
V. salmonicida). We also included 16 presumptive
Vibrio isolates associated with healthy and bleached corals.
In order to determine the intraspecies variation among the three loci,
we included at least three representative strains each of 37
Vibrionaceae species. The aim of this study was to evaluate
the application of different genetic loci as phylogenetic and
identification markers, both individually and as concatenated elements.
The multigene-based phylogeny roughly confirmed the 16S rRNA gene-based
grouping obtained in previous studies and revealed new interesting
relationships among different Vibrio
species.

MATERIALS AND METHODS
The strains used for this study are listed in Table
1. All strains
included in this study are deposited in the BCCM/LMG
Bacteria
Collection or the Research Collection at Ghent University
(Ghent,
Belgium). A detailed list of these strains can be found
elsewhere
(
31,
40). This study also
included fresh isolates associated
with bleached and healthy corals of
different species collected
in 2002 in Australia and the United States.
Isolates R-21409,
R-21422, and R-21431 originated from different
bleached
Pachyseris speciosa colonies (Magnetic Island,
Australia). R-21410 originated
from a healthy
Montipora
capitata sample, and isolates R-21416
and R-21432 originated from
a healthy
P. speciosa sample, both
in Kaneohe Bay (United
States). R-21415, R-21419, and R-21433
were isolated from healthy
Merulina ampliata samples (Magnetic
Island, Australia), and
R-21413 was isolated from bleached
M. ampliata coral (Magnetic
Island, Australia). R-21427 and R-21434
originated from bleached
Acropora millepora coral (Davies Reef,
Australia). R-21426,
R-21435, and R-21439 were isolated from
healthy
A. millepora
(Davies Reef, Australia),
Pocillopora damicornis (Davies Reef,
Australia), and
Barabattoia amicorum (Magnetic
Island,
Australia) samples, respectively. R-23286 was isolated
from a bleached
Montipora sp. sample (Magnetic Island, Australia)
in
2003.
Bacterial genomic DNAs were extracted according to the
methodology
described by Pitcher et al.
(
24). PCRs were performed
essentially
as described previously
(
30). The
sequences of the primers used
for amplification and sequencing are
listed in Table
2. These
primers were designed using 17 gene sequences of each locus
of
Vibrio cholerae (n16961_o1),
V.
parahaemolyticus (o3k6_rimd2210633),
V.
vulnificus (cmcp6),
Escherichia coli (cft073,
o157h7_edl933,
o157h7_rimd0509952, and
k12_mg1655),
Shigella flexneri (2a_2457t
and
2a_301),
Salmonella enterica (ct18 and
ty2_typhi 3),
S. enterica serovar Typhimurium
(lt2sgsc1412_atcc700720),
Yersinia pestis (co92 and
kim),
Haemophilus influenzae (rd),
Pasteurella
multocida (pm70), and
Shewanella oneidensis (mr1), which
originated from
publicly available data from whole-genome sequencing
projects.
All of the primers specifically amplified the target
fragments
of all currently known strains of vibrios.
PCR mixtures
were composed of 29.5 µl sterile MilliQ water,
5.0 µl
PCR buffer (10
x), 5.0 µl deoxynucleoside
triphosphates
(2 mM each), 2.5 µl forward primer rpoA-01-F
(10 µM),
2.5 µl reverse primer rpoA-03-R (10 µM),
0.5 µl
AmpliTaq DNA polymerase (1 U/µl), and 5.0
µl template
DNA (0.01 µg/µl). PCRs were performed
using a GeneAmp
PCR System 9600 thermocycler (Applied Biosystems).
The thermal program
consisted of (i) 5 min at 95°C; (ii)
3 cycles of 1 min at
95°C, 2 min 15 s at 55°C, and 1
min
15 s at 72°C; (iii) 30 cycles of 35 s at
95°C, 1
min 15 s at 55°C, and 1 min
15 s at 72°C; and (iv) a
final 7 min at 72°C.
PCR products with the expected size
and intensity were purified using
the Nucleofast 96 PCR cleanup
system (Macherey-Nagel, Germany).
Purified PCR products were
eluted in 30 to 200 µl sterile
MilliQ water. Subsequently,
3.0 µl of purified PCR
product was mixed with 1.0 µl
ABI Prism Big Dye Terminator
ready reaction mix, version 3.1
(Applied Biosystems), 3.0 µl
sequencing primer (4 µM),
1.5 µl dilution buffer
(5
x), and 1.5 µl MilliQ water.
The thermal program
consisted of 30 cycles of 15 s at 96°C,
1 s
at 35°C, and 4 min at 60°C. Sequencing products
were
purified using a Montage SEQ
96 sequencing reaction cleanup
kit
(Millipore). Purified sequencing reactions were eluted in 20
µl
of injection solution and mixed with 20 µl of
deionized
formamide. Subsequently, separation of the DNA fragments was
obtained
in an ABI PRISM 3100 genetic analyzer (Applied Biosystems).
The
time and voltage of sample injection were 20 s and 1.25
kV.
Each run was performed at 50°C for 6,500 s at 0.1 mA and
12.2
kV. Raw sequence data were transferred to the Gene Builder module
within
Kodon package 2.03 (Applied Maths, Belgium), where consensus
sequences
were determined using the two to four reads. Consensus
sequences
were imported into BioNumerics 3.0 software (Applied Maths,
Belgium),
where a similarity matrix and phylogenetic trees were created
based
on the maximum parsimony and neighbor joining methods
(
27).
Splits tree
decomposition analysis was done using software available
on the
Internet
(
http://bibiserv.techfak.uni-bielefeld.de/splits/)
(
13),
while the GC
content, ratio of mean synonymous substitutions
per
synonymous site to mean nonsynonymous substitutions per
nonsynonymous
site (
dS/
dN),
and Sawyer's test were calculated using the software
package
START obtained from
http://pubmlst.org/software/analysis/start/
(
15).

RESULTS AND DISCUSSION
We sequenced fragments of the
rpoA (931
nt),
recA (613 to 783
nt), and
pyrH (443 nt) genes of
192 vibrios corresponding to
60 to 93% of the coding regions of these
genes (EMBL accession
no.
AJ842347
to
AJ842743).
The GC contents of
rpoA (46% ±
0.9%),
recA
(46.6% ± 1.9%), and
pyrH (48.7% ±
0.9%) are
within the average for the total genomes of vibrios
(
34-
39).
We
compared the
rpoA,
recA,
pyrH, and 16S
rRNA pairwise similarities
using Pearson's product-moment correlation
coefficient. A significant
correlation was obtained between 16S rRNA
and the three loci
(
R = 0.81 for
rpoA and
0.68 for
recA and
pyrH). The
rpoA and
16S
rRNA data had a linear relationship, whereas the
pyrH and
recA data were best fitted with a polynomial regression of the
second
degree. These significant correlations show that
rpoA,
recA,
and
pyrH are indeed phylogenetic markers in
vibrios. The gene
sequences of these three loci have high proportions
of synonymous
mutations (
dS/
dN
= 29 for
rpoA and
recA and 39 for
pyrH), suggesting
that there is selection against amino acid
changes in these
genes
(
6).
The families
Vibrionaceae, Photobacteriaceae,
Enterovibrionaceae, and Salinivibrionaceae were
clearly separated from one another on the basis of the four loci (Fig.
1). The five currently known genera of vibrios were all differentiated on
the basis of the gene sequences (Fig.
1). Enterovibrio
strains had 95.4 to 100%, 88.6 to 100%, and 85.6 to 99.8%
rpoA, recA, and pyrH gene sequence
similarity, respectively. Grimontia hollisae and E.
coralii had 96.2%, 85%, and 86% rpoA, recA, and
pyrH sequence similarity, respectively. The new species E.
coralii was tentatively allocated to the genus
Enterovibrio on the basis of polyphasic taxonomic analysis
(41), but we anticipate
that this organism may be allocated to a new genus in future studies.
Photobacterium species had 90.4 to 100%, 80 to 100%, and 79 to
99.6% rpoA, recA, and pyrH sequence
similarity, respectively. Strains of the genus Vibrio showed
the highest gene sequence variation, with ca. 19% variation for
rpoA and 27% variation for recA and pyrH.
V. logei, V. fischeri, and V. wodanis
grouped apart from the other genus members, suggesting that
Vibrio species are polyphyletic. The two squid symbionts had
96.6, 84, and 86% rpoA, recA, and pyrH
sequence similarity, respectively.
Within the
Vibrionaceae, some pairs of highly related species,
i.e.,
V. aerogenes-
V. gazogenes,
V.
fluvialis-
V. furnissii,
V. cholerae-
V.
mimicus,
V. diazotrophicus-
V. hispanicus,
V.
ichthyoenteri-
V. scophthalmi, and
V.
anguillarum-
V. ordalii, appeared in the
different
phylogenetic trees. These pairs are indeed known to
have highly related
genomes, with about 70% DNA-DNA similarity.
V. halioticoli-,
V. harveyi-,
V. splendidus-, and
V.
tubiashii-related
species formed groups in each tree. Roughly, the
grouping of
Vibrio species obtained with different genes is in
agreement
with that in previous polyphasic taxonomy studies
(
31-
38,
40).
V.
harveyi-related species had at least 96.5%, 97%, and 95%
rpoA,
recA, and
pyrH gene sequence
similarity, respectively.
V. harveyi was closely related to
V. parahaemolyticus (98.8 to 99%), but
it had only 96.5%, 97.4
to 97.7%, and 91 to 95%
rpoA,
recA,
and
pyrH
gene sequence similarity, respectively, to its sister
species
V.
campbellii and
V. rotiferianus
(
9).
V. harveyi
LMG
11659, LMG 20370, and R-14913 clustered apart from the other
cospecific
strains, having 98.3% similarity to the other
V.
harveyi strains.
These three strains were found in the former AFLP
clusters A30
and A31 (
31)
and had about 70% DNA-DNA similarity with
V. harveyi LMG
4044
T, suggesting that they may belong to a new species
(
10).
The gut abalone
vibrios were all grouped together with at least
91.2, 97, and 93%
rpoA,
recA, and
pyrH similarity,
respectively.
V. halioticoli,
V. ezurae, and
V.
neonatus grouped together
(93 to 99.5%) in all trees. The gut
abalone vibrios have similar
16S rRNA sequences (

98%)
(
12,
28), indicating that the
three
loci studied here are alternatives for the identification of
these
organisms. It is also evident that the three genetic loci are
useful
for the identification of the species
V.
nigripulchritudo,
V. penaeicida,
V. tapetis,
V. mediterranei,
V. rumoiensis,
V.
proteolyticus,
V. metschnikovii, and
V.
cincinnatiensis, as they had <96%
gene sequence similarity
with their closest neighbors.
The high similarity of genomes
found among different species of vibrios, e.g., in the V.
splendidus- and V. tubiashii-related groups, may be
explained by niche adaptation
(4). V.
splendidus-related species probably coexist in the same
environment. These organisms have been associated with bivalve mollusks
and with the so-called summer mortality syndrome
(19). According to Cohan
(4), natural selection is
the main driving force in the evolution of bacterial species. He
suggests that sexual isolation is not a milestone in the origin and
maintenance of bacterial species. Indeed, candidate gene transfers,
including paralog acquisition or the displacement and acquisition of
new genes, have been detected in 5.6% (215 genes) of the genome of
V. cholerae N16961
(17). Horizontal gene
transfer (HGT) may indeed be an important force in the evolution of
vibrios. The positions of various pairs of species, e.g., V.
hispanicus and V. diazotrophicus, V. mytili and
V. diabolicus, V. coralliilyticus and V.
neptunius, and V. brasiliensis and V. tubiashii,
changed in the trees constructed from the different genetic loci,
suggesting that recombination might have occurred among these vibrios.
Although rpoA and recA are thought to belong to the
bacterial core genome and for this reason may be refractory to HGT
(11), a recent study
reported the HGT of rpoA in Aquifex,
Thermotoga, and Fusobacterium
(14). Our study did
provide clear evidence of gene conversion events in the rpoA,
recA, and pyrH (P < 0.05) genes of
V. splendidus- and V. tubiashii-related species using
Sawyer's test. In addition, our splits-tree decomposition analysis
revealed a network-like tree for these groups (Fig.
2). The presence of parallelograms in splits trees is a hallmark of
recombination (6). Thus,
we may conclude that recombination is a rather common evolutionary
process within different species of vibrios. Due to such
recombinational events, different vibrios, e.g., V. tubiashii-
and V. splendidus-related species, may group close to one
another, hampering their identification. In order to overcome the
effects of gene conversion and recombination in species identification,
several loci should be indexed simultaneously and used to construct
multigene phylogenetic trees. The four families of vibrios were clearly
apart from one another in our multigene tree (Fig.
3). The groups obtained with this tree corresponded to those in the
single-locus trees, except for the position of V. mediterranei
along with those of V. tubiashii-related species. All species
had <97% concatenated sequence similarity, with the exception
of the pairs V. coralliilyticus-V. neptunius and
V. anguilarum-V. ordalii.
So far, there is not
a single gene that can differentiate well
all species of vibrios.
Different genes show different degrees
of discrimination according to
the group of vibrios under analysis.
For instance,
V.
cyclitrophicus,
V. splendidus,
V. pomeroyi,
and
V. chagasii had about 99%
rpoA sequence similarity.
V. splendidus-related
species are indeed highly related,
having little variation (<2%)
in
gyrB and 16S rRNA
gene sequences, phenotypic features, and
DNA-DNA hybridization
(
19,
36). On the other hand,
these species
have <97%
recA and
pyrH gene
sequence similarity (except
for
V. lentus and
V.
splendidus, which have 97.2% gene sequence
similarity)
(
30). Nevertheless, the
different
V. splendidus-related
species clearly formed
separated clusters on the basis of the
three loci, suggesting that
these genes are indeed useful for
the differentiation of highly related
species.
Another interesting example of high gene sequence
similarity in different loci is found within the V.
tubiashii-related species. These organisms had at least 92.9%
rpoA gene sequence similarity. V. coralliilyticus had
98.2, 97.9, 97.1, and 95.1% rpoA sequence similarity with
V. xuii, V. neptunius, V. nereis, and V.
tubiashii, respectively. The corresponding 16S rRNA similarity
values were 96.9, 98.2, 96.7, and 97.1%, respectively
(35), while those for
pyrH (except those for V. neptunius and V.
coralliillyticus, which had a 96% sequence similarity) and
recA were below 87 and 97%, respectively. V.
tubiashii and V. brasiliensis had a 98.2% gene sequence
similarity for both rpoA and 16S rRNA
(35). Overall,
rpoA and 16S rRNA gene sequences have similar discriminatory
powers for V. tubiashii-related species that are inferior to
those of recA and pyrH
(40). V.
pacinii, V. pectenicida, and the pair V.
scophthalmi-V. ichthyoenteri had <96%
rpoA gene sequence similarity to V. tubiashii-related
species, suggesting that this gene is useful for the identification of
these species. Overall, rpoA gene sequences were more
discriminatory than 16S rRNA sequences. 16S rRNA and recA
similarities above 97 and 94% corresponded to rpoA
similarities above 88 and 97%, respectively. This fact highlights the
need for future studies aiming at additional loci.
Vibrios have
been implicated in the phenomenon of coral bleaching
(2,
25). We used
rpoA gene sequences to allocate taxonomically fresh isolates
of vibrios associated with coral bleaching. These isolates were
identified as V. fortis, V. campbellii, V.
coralliilyticus, V. harveyi, V. mediterranei,
and V. rotiferianus, suggesting that the process of coral
bleaching may be carried out by different Vibrio species.
V. harveyi has been implicated in diseases of a wide range of
marine animals (1),
including different coral species
(10,
29). Although vibrios
isolated in Hawaii were always associated with healthy corals, our data
suggest that highly related strains of potentially pathogenic vibrios,
e.g., R-21432 and R-23286, are present in both Kaneohe Bay (Hawaii) and
the Great Coral Barrier (Australia). Environmental conditions in
Australia may favor the prevalence of coral infection caused by
vibrios, but this remains to be determined in future
studies.
Considerable numbers of representative strains of the
species V. campbellii (n = 9), V.
cholerae (n = 10), V. coralliilyticus
(n = 9), V. harveyi (n =
14), and V. mediterranei (n = 7) were
examined in this study in order to unambiguously determine the
intraspecies variation of rpoA, recA, and
pyrH gene sequences. The intraspecies gene sequence
heterogeneity for most species was well below 2, 6, and 6%,
respectively (Table 1).
Overall, the 192 type and reference strains represent well the
currently known genomic diversity of most Vibrionaceae
species. Strains within each of the examined species fulfill the
criteria of a
60% mutual AFLP pattern similarity,
70% DNA-DNA similarity, and
97.5% 16S rRNA gene
sequence similarity. Representative strains were selected in order to
represent the currently known genomic diversity of these species. The
V. cholerae strains, for instance, comprise the serogroups O1,
O139, and non-O1/non-O139 and represent the known genomic diversity of
this species, as revealed by FAFLP analysis
(39,
40). We could therefore
conclude that strains of the same species will have at least 98%, 94%,
and 94% sequence similarity in the rpoA, recA, and
pyrH genes, respectively.
The data generated in this
study are well suited to be used for the rapid detection and
identification of pathogenic vibrios in the environment
through, e.g., real-time PCR
(3,
7). The data
could also be an alternative to 16S rRNA gene sequences in
studies of the ecology and community dynamics of vibrios in coastal
waters (42,
43). The advantages of
the loci studied here are that they belong to the bacterial core genome
(11), have
a high phylogenetic signal, and are single-copy
genes and that different species of vibrios have
different gene sequences that thus enable the reliable identification
of these organisms. Our multilocus sequence analysis data
will be used as the basis for the creation of a free-access
online identification system for vibrios
(http://lmg.ugent.be/bnserver/MLSA/Vibrionaceae/).Work is under way on other genes, including the atpA,
obg, uvrB, pheS, and serS genes
encoding tRNA synthases and thd, which together will enhance
the discrimination of all currently recognized species of
vibrios.

ACKNOWLEDGMENTS
F.L.T. acknowledges a
postdoctoral fellowship from BCCM/LMG
Bacteria Collection (Ghent,
Belgium) and a young researcher
fellowship from FAPESP, Brazil (no.
2004/00814-9). D.G. acknowledges
financial support from BOF (project
no. 01110803). J.S. acknowledges
grants from the Fund for Scientific
Research (FWO), Belgium.
S.N. acknowledges a Ph.D. scholarship from the
Palestinian Ministry
of Higher Education.
We thank K.
Vandemeulebroecke and R. Coopman for their technical assistance. We
thank M. Maiden (University of Oxford) for suggestions in the early
stages of this
work.

FOOTNOTES
* Corresponding author. Mailing address: Microbial Resources Division and Brazilian Collection of Environmental and Industrial Micro-Organisms (CBMAI), CPQBA, UNICAMP, CP 6171, 13081-970 Campinas, Brazil. Phone: 55-19-38847500. Fax: 55-19-38847811. E-mail:
Fabiano.Thompson{at}terra.com.br.


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