genetic analysis of the capsular polysaccharide synthesis locus in 15 streptococcus suis serotypes

R E S EA RCH L E T T E R

Genetic analysis of the capsular polysaccharide synthesis locusin 15 Streptococcus suis serotypes

Kaicheng Wang1,2,3, Weixing Fan3, Lijuan Cai3, Baoxu Huang3 & Chengping Lu1,2

1Key Lab Animal Disease Diagnostic & Immunology, Ministry of Agriculture, Nanjing Agricultural University, Nanjing, China; 2College of

Veterinary Medicine, Nanjing Agricultural University, Nanjing, China; and 3China Animal Health and Epidemiology Center, Qingdao, China

Correspondence: Chengping Lu, College of

Veterinary Medicine, Nanjing Agricultural

University, Nanjing 210095, China. Tel.:

+86 02584396517; fax: +86 02584396517;

e-mail: [email protected]

Received 8 April 2011; revised 22 August

2011; accepted 22 August 2011.

Final version published online 21 September

2011.

DOI: 10.1111/j.1574-6968.2011.02394.x

Editor: Mark Enright

Keywords

capsular polysaccharide; gene locus;

Streptococcus suis.

Abstract

The capsular polysaccharide (CPS) synthesis locus of 13 Streptococcus suis sero-

types (serotype 1, 3, 4, 5, 7, 8, 9, 10, 14, 19, 23, 25 and 1/2) was sequenced

and compared with that of serotype 2 and 16. The CPS synthesis locus of these

15 serotypes falls into two genetic groups. The locus is located on the chromo-

some between orfZ and aroA. All the translated proteins in the CPS synthesis

locus were clustered into 127 homology groups using the TRIBEMCL algorithm.

The general organization of the locus suggested that the CPS of S. suis could

be synthesized by the Wzy-dependent pathway. The capsule of serotypes 3, 4,

5, 7, 9, 10, 19 and 23 was predicted to be amino-polysaccharide. Sialic acid

was predicted to be present in the capsule of serotypes 1, 2, 14, 16 and 1/2.

The characteristics of the CPS synthesis locus suggest that some genes may

have been imported into S. suis (or their ancestors) on multiple occasions from

different and unknown sources.

Introduction

Streptococcus suis can cause meningitis, septicaemia, endo-

carditis, arthritis and septic shock in pigs. Based on varia-

tion in capsular antigens, 33 serotypes (1–31, 33 and 1/2)

of S. suis have been identified so far (Lun et al., 2007).

Each serotype has a structurally distinct capsular polysac-

charide (CPS), composed of repeating oligosaccharide units

joined by glycosidic linkages. The expression of the capsule

is strongly associated with the ability of S. suis to cause

invasive disease (Smith et al., 1999a). The S. suis serotype 2

strains without CPS proved to be avirulent in murine and

pig models of infection (Charland et al., 1998).

The biosynthesis of CPS requires a complex pathway

and, generally, the genes involved in this process are clus-

tered in a single locus (Roberts, 1996). Moreover, in many

gram-positive and gram-negative bacteria, these CPS syn-

thesis loci (cps loci) show a common genetic organization.

The cps locus typically encodes the enzymes to build the

repeat unit, including an initial glycosyl phosphate trans-

ferase, and additional transferases responsible for the for-

mation of the linkages, and allows for the addition of

sugars (or other moieties) or other modifications of the

repeat unit, as well as a repeat-unit flippase and polymer-

ase (Roberts, 1996). The cps locus of S. suis serotype 2 was

certified to be closely linked on the chromosome (Smith

et al., 2000). With the exception of the entire cps locus

sequence of serotype 2, only partial sequences of cps locus

in serotypes 1, 7 and 9, and the entire serotype 16 cps

locus are available (Smith et al., 1999a, b, c; Wang et al.,

2011); those of all the other serotypes remain unknown.

Studies on the cps locus would contribute to unravel-

ling the CPS biosynthetic pathway and the evolution of

cps locus, and open up the prospect of the design of

inhibitors capable of obstructing the virulence factor pro-

duction. In this paper the sequences of the cps locus for

13 serotypes (serotypes 1, 3, 4, 5, 7, 8, 9, 10, 14, 19, 23,

25 and 1/2) were obtained and analyzed together with

those of serotypes 2 and 16.

Materials and methods

Bacterial strains and genomics DNA isolation

The S. suis reference strains 1, 3, 4, 5, 7, 8, 9, 10, 14, 19, 23,

25 and 1/2 were obtained from M. Gottschalk (Department

FEMS Microbiol Lett 324 (2011) 117–124 ª 2011 Federation of European Microbiological SocietiesPublished by Blackwell Publishing Ltd. All rights reserved

MIC

ROBI

OLO

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LET

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of Pathogenic Microbiology, Montreal University, QC,

Canada) (Harel et al., 1994). Streptococcus suis strains were

grown in Todd–Hewitt broth (code CM189; Oxoid) and

plated on Columbia agar blood base (code CM331; Oxoid)

containing 6% (v/v) sheep blood. Genomic DNA of

bacterial strains was isolated and purified with the Wizard

Genomic DNA Purification kit (Promega).

PCR and DNA sequencing

PCR reactions were performed using the LA-Taq (Takara,

Japan), which contains proof-reading thermostable poly-

merases. The conserved region of the locus was amplified

by the primers P1 (5′-attacaggtgggctatcgggt) and P2

(5′-cgtcatttcgttcactgcttc) according to the orfZ and cpsD

genes in the serotype 2 cps locus. The type-specific region

of the serotype 1 cps locus was amplified using primers

P3 (5′-tgacgctacttgggctaactcccgtacttg) and P4 (5′-gcttgc-ttcttgacccttttcccttttcta) in cpsD and IS30. The primers P5

(5′-cacttaatggctcgtgctatattctctt) and P6 (5′-gttccctttagtttttc-tacgcttcttc) focusing on the conserved cpsD and aroA

were used to amplify the type-specific region of the cps

locus in the other 12 serotypes. PCR fragments amplified

by P1 and P2 were cloned into pCR-XL-TOPO vector

(TOPO XL PCR Cloning kit; Invitrogen) and transformed

to TOP10 Chemically Competent Escherichia coli (Invitro-

gen). Clones were sequenced by primer walking from

each end using Big-Dye terminator chemistry on ABI3730

sequencing machines. PCR fragment amplified by P3 and

P4 (P5 and P6) was used directly to construct small-

insert libraries (McMurray et al., 1998), with 2- to 3-kb

inserts in pUC-18. Clones from the library were

sequenced from each end using Big-Dye terminator

chemistry (Applied Biosystems) on ABI3730 sequencing

machines, to give an average of six- to eight-fold cover-

age. The sequence of the fragments amplified by P1/P2

and P3/P4 (P5/P6) of each serotype was assembled as one

containing the entire cps locus.

Sequence annotation and bioinformatic

analysis

The promoters and terminators of the sequenced cps locus

were predicted using the BPROM and FINDTERM program

(http://linux1.softberry.com/berry.phtml), respectively. ORFs

were analyzed using the VECTOR NTΙ program. Genes

were named according to the polysaccharide gene nomen-

clature of S. suis serotype 2 (Smith et al., 2000). The cps

locus of serotype 2 (GenBank accession no. AM946016.1,

position: 549929–578963) and 16 (GenBank accession no.

HQ694980) were analyzed together with the sequenced

locus. Predicted proteins in the serotype 15 cps locus

were clustered into homology groups (HGs) using SCPS

(Nepusz et al., 2010) with the TRIBEMCL algorithm (Enright

et al., 2002) with a cut-off of 1e�50. The cps gene products

were classified into Pfam families based on hidden Markov

model profiles using the PFAM database (http://www.sanger.

ac.uk/Software/Pfam/) (Finn et al., 2010). The gene name

according to the bacterial polysaccharide gene nomencla-

ture system (Reeves et al., 1996) (www.microbio.usyd.edu.

au/BPGD) was also listed for HGs. The phylogenetic trees

for the 15 serotype cps locus were generated by the

neighbour-joining method using the program MEGA

(version 4) (Tamura et al., 2007). Visual representation of

the alignments using nucleotide similarities (tblastx) of the

cps locus were performed with the Artemis Comparison

Tool (ACT) (Carver et al., 2005). The nucleic acid or

translated proteins were compared with those in GenBank

database by the BLAST network service (http://blast.ncbi.

nlm.nih.gov/Blast.cgi).

Results and discussion

DNA sequence of the cps locus for S. suis

serotypes 1, 3, 4, 5, 7, 8, 9, 10, 14, 19, 23, 25

and 1/2

The cps loci of the 13 S. suis serotypes was amplified and

sequenced. The length of the amplicons amplified by P1

and P2 is about 7 kb. The length of the amplicons ampli-

fied by P3 and P4 (P5 and P6) ranged from 11 to 28 kb.

The sequence of the two fragments in each serotype was

assembled as one containing the entire cps locus. For S.

suis serotypes 1, 3, 4, 5, 7, 8, 9, 10, 14, 19, 23, 25 and 1/2,

sequences of 26 419, 24 251, 26 593, 29 167, 26 574,

18 592, 24 015, 25 729, 32 787, 30 791, 26 905, 18 672,

and 35 174 bp were obtained, respectively. The DNA

sequences were deposited in GenBank under accession

numbers JF273644–JF273656. Genes included in the cps

locus are orientated in the same direction. The promoters

of all loci are located in orfY and orfX at the 5′ end of the

cps locus. The number of orfs in the transcription units

related to CPS synthesis ranges from 14 to 29 (Figs 1 and

2, Table 1). The general organization of the 13 new

clusters is similar to that of S. suis serotype 2 and 16 cps

clusters. The length and G + C content of the 15 serotypes

cps locus are listed in Table 1. All of the 15 known cps loci

are located on the chromosome between orfZ and aroA,

with a cassette-like structure: type-specific genes are

flanked by conserved genes common to most gene clus-

ters. This type of cps cluster is also found in other strepto-

coccus species (Wessels, 1997), including Streptococcus

pneumoniae, Streptococcus agalactiae and Streptococcus

thermophilus. Although the aroA gene is conserved in all

serotypes, the other sequence at the 3′ end of the cps locus

is quite different. The site of the terminator and the

ª 2011 Federation of European Microbiological Societies FEMS Microbiol Lett 324 (2011) 117–124Published by Blackwell Publishing Ltd. All rights reserved

118 K. Wang et al.

sequence of the flanking genes are different among the

serotypes, resulting in the different length of the flanking

genes at the 3′ end of the cps locus (Figs 1 and 2). The 15

cps loci fall into two genetic groups using the neighbour-

joining method with the program MEGA (groups 1 and 2,

Figs 1 and 2).

Assignment of HGs

The biosynthesis of CPS is a complex enzymatic pathway

formed by the regulatory proteins, glycosyltransferase

(GT), polymerization, flippase and other transferases

expressed by the genes contained in the cps locus (Rob-

erts, 1996). Functional designations were assigned to the

products of the 281 predicted coding sequences in the 15

cps regions. To make more specific assignments within

coding sequences, the TRIBEMCL algorithm was used to

assemble all proteins into HGs. Seventy percent of the

proteins were assembled into 42 HGs (Supporting Infor-

mation, Table S1), containing 2–15 members each. The

remainder of the proteins form 85 single-member HGs.

The products of wzg, wzz, wzd and wze each fall into a

single HG, which is contained in every serotype. These

four HGs (Wzg, Wzz, Wzd, and Wze) are the largest

groups. The next largest HG consists of nine WcdA

CapD-like proteins (HG4), followed by six WchA initial

glycosylphosphotransferases (HG5). There are 12 groups

of Wzy repeat-unit polymerases and nine groups of Wzx

flippases. A pseudogene in serotype 8 cps locus is caused

by frame shift.

wzg, wzz, wze and wzd genes are conserved in

all CPS types

The first four genes, wzg, wzz, wze and wzd (also known

as cpsABCD), are conserved with high sequence identity

in all 15 serotypes. Wzg and Wzz proteins were predicted

to play an important role in the synthesis regulation and

the chain length determination of CPS in the S. suis sero-

type 2. Isogenic mutants in wzg gene cannot produce CPS

(Smith et al., 1999a, b, c). The exact function of Wze and

Wzd in S. suis is unknown. wze and wzd were also found

in other Streptococcus capsule gene clusters (Wessels,

1997). The two proteins are in the MPA1 class of the

Paulsen et al. (1997) classification and are thought to be

involved in polysaccharide export. It was reported that

Fig. 1. Comparisons of the genetic group 1 cps locus. The color keys for the functional classes of genes in the cps locus are shown at the

bottom.


cps locus of Streptococcus suis 119

Wzd is a tyrosine kinase and Wze is a substrate for Wzd

kinase in S. pneumoniae (Morona et al., 2003) and the

Wzd and Wze proteins may play similar roles in S. suis.

Initial transferases, polymerization and

flippase

The initial glycosylphosphotransferases are responsible for

linkage of an activated glycosylphosphate to the lipid

carrier (Pelosi et al., 2005). The initial glycosylphospho-

transferases of all the 15 serotypes fall into four HGs

(WchA, WciI, WcaJ and WcgA). In the group 2 (serotypes

1, 2, 8, 14, 16, 25 and 1/2) cps locus, all the initial transfer-

ase genes are wchA, the products of which can add glucose-

1-phosphate to undecaprenol phosphate to create Und-PP-

Glc (Kolkman, et al., 1997). wchA is absent in the group 1

(serotype 3, 4, 5, 7, 9, 10, 19 and 23) cps locus. The product

of the fifth cps gene is a CapD-like protein (WcdA), which

can generate amide bonds with peptidoglycan cross-bridges

to anchor capsular material within the cell wall envelope

(Candela & Fouet, 2005). In the group 1 locus, the initial

transferase genes (wciI, wcaJ and wcgA) are downstream of

wcdA. Because the exact composition and structure of most

S. suis serotypes CPS is unknown, the transferred sugars of

the initial transferases can only be suspected, based on the

function of similar proteins of other bacteria. WciI proteins

Fig. 2. Comparisons of the genetic group 2 cps locus. The color keys for the functional classes of genes in the cps locus are same to that in Fig. 1.

Table 1. Properties of the cps locus in 15 serotypes

Serotype

Length of

the cps

locus*

(bp)

Number of

orfs†

G + C content

of cps

locus/genome

(%) Initial transferases

HG of

Wzy

HG of

Wzx

Number

of GTs‡

1 21 635 21 36.55/unknown WchA HG29 HG7 5

2 26 423 28 36.23/41 WchA HG32 HG7 6

3 17 055 15 35.92/41 WcgA HG48 HG47 2

4 17 658 16 34.08/unknown WcaJ HG55 HG57 4




9 15 103 14 34.69/unknown WciI HG64 HG37 4

10 20 516 21 34.49/unknown WciI HG80 HG71 5

14 24 723 29 35.48/41 WchA HG29 HG7 5





1/2 26 445 28 36.04/unknown WchA HG32 HG7 6

*From transcription initiation site to terminator.†Ignoring flanking genes.‡GTs, including initial transferases.


120 K. Wang et al.

showed a high degree of similarity to that of S. pneumoniae

serotype 4 (62% identity). The transferred initial sugar for

WciI in S. suis was predicted to be N-acetylgalactosamine

pyranose (GalpNAc) or N-acetylglucosamine pyranose

(GlcpNAc) (Bentley et al., 2006). Streptococcus suis WcaJ

proteins are similar to the smi_0538 protein with unknown

transferred sugars (60% identity) of Streptococcus mitis B6

strain (accession number: NC_013853.1). Streptococcus suis

WcgA proteins are similar to the BpOF4_06575 protein

predicted to be UDP-galactose phosphate transferase (71%

identity) of Bacillus pseudofirmus OF4 (accession number:

NC_013791).

The initial sugar of the repeat unit is also the donor

sugar in the polymerization of the repeat units. The spec-

ificity of the Wzy polymerase determines the other com-

ponent of the CPS linkage (Bentley et al., 2006). The

Wzy polymerase is quite different in the 15 serotypes.

There are five polymerase HGs associated with WchA,

two with WciI, 5 with WcaJ and one with WcgA

(Table 1). These associations are mostly exclusive, with

only one polymerase HG (HG39) associated with two

HGs of initial transferases. In such cases, the linkages

may involve the same acceptor sugar anomerism (a or bisomer) and the same or closely related donor sugar. Wzx

flippase can transport the repeat unit across the cytoplas-

mic membrane after CPS polymerization. Except for sero-

type 16, only one wzx gene is located in the S. suis cps

locus. Two wzx genes (cps16N and cps16R) exist in the

cps16 locus. cps16O is similar to transposase gene (83%

identity) of Streptococcus mutans at the nucleic acid level.

cps16N may be inactivated in the transposition-like events

caused by Cps16O transposase. In the serotype 1, 2, 14,

16 and 1/2 cps locus, all the flippases belong to HG7.

Each Wzx protein may transport polysaccharides with a

similar composition and/or structure (Liu et al., 1996).

The composition and/or structure were predicted to be

similar in the five serotypes.

GT and other transferases

GTs are important enzymes that catalyze the attachment

of sugars (donor) to an aglycone (acceptor) in CPS syn-

thesis. Ignoring initial glycosylphosphotransferase, GTs in

all 15 cps loci fall into 38 HGs. Two to seven GTs exist in

each cps locus (Table 1). The predicted function of each

GT HG is listed in Table S1. A putative GT enhancer

(wchJ) is located in serotype 1, 14, 16 and 25. The mech-

anism and substrate of these enhancers are unknown.

Aminotransferase genes are present in the serotype 3,

4, 5, 7, 19 and 23 cps loci. Amino-sugars are important

components of some bacterial capsules (Hofmann et al.,

1985; Beynon et al., 1990; Flahaut et al., 2008). Amin-

otransferases can transfer amino groups to sugars or form

amino linked amidically to the carboxyl group (Beynon

et al., 1990). We predicted that the CPS of serotypes 3, 4,

5, 7, 19 and 23 should be amino-sugar. Twelve different

putative HGs of acetyltransferase, which play an impor-

tant role in CPS structure determination (Calix & Nahm,

2010), are present in the 15 cps locus.

Five genes (neuA, B, C, D and sialyltransferase)

involved in sialic acid synthesis exist in the serotype 1, 2,

14, 16 and 1/2 cps loci. Because the identities of the genes

involved in sialic acid synthesis between serotype 16 and

2 are very low (Wang et al., 2011), the presence of genes

involved in sialic acid synthesis was predicted only for

serotypes 1, 2, 14, 27 and 1/2 in the cross-hybridization

experiments (Smith et al., 2000). In sialic acid detection,

only types 1, 1/2, 2, 14, 15, and 16 agglutinated with lec-

tin (Charland et al., 1995). CPS of serotypes 1, 2, 14, 16

and 1/2 was predicted to contain sialic acid, which can

enhance intracellular survival, participate in biofilm for-

mation, or mask underlying antibody epitopes (Severi

et al., 2007).

The cps10 locus contains the putative glycerol phos-

photransferase gene (wcxP). Serotype 10 CPS may be

composed of glycosylglycerol repeating unit, which exists

in the CPS of other microorganisms (Altman et al.,

1987a, b; Beynon et al., 1991). The metalloprotease (wcyI)

and pyruvyltransferase (whaL) was only found in sero-

types 7 and 23, respectively. Pyruvyltransferase is identi-

fied as an enzyme which can transfer pyruvate

substitutions into CPS saccharide intermediates (Lew &

Heidelberger, 1976; Kim et al., 2002). The function of

metalloprotease in the cps7 locus is unknown. Nucleo-

tidyltransferases are contained in the cps locus of sero-

types 3 and 9. Putative LicD-family phosphotransferases

are contained in the locus of serotypes 8, 9 and 25.

Comparison of the cps locus of serotypes 1, 2,

14 and 1/2

There are one-way or two-way cross-reactions in some S.

suis serotypes. Two-way cross-reactions between serotypes

1/2 and 1, and serotypes 1/2 and 2 were detected. A one-

way cross-reaction was detected between types 1 and 14

(Higgins & Gottschalk, 1990). The comparison results

showed that the cps loci of serotypes 1, 2, 14 and 1/2 are

similar (Fig. 2). With the exception of serotype 1/2, the

serotypes can infect not only pigs but also humans, and

can cause disease and/or death (Heath et al., 1996; Vila-

ichone et al., 2002; Haleis et al., 2009; Kerdsin et al.,

2009; Gottschalk et al., 2010). The similar CPS produc-

tion was predicted to be one of the reasons for the high

pathogenicity of the three serotypes.

The cpsK-T fragments of all four serotypes are highly

similar. The cpsE–J fragments of serotypes 1 and 14 are



similar, but are different from that of serotypes 2 and

1/2. The cpsE-J fragments of serotypes 2 and 1/2 are also

similar. The serotype 1 cps locus lacks a 906-bp fragment

containing IS630-Spn1 transposase in the S. suis serotype

2 cps locus, resulting in the earlier transcription termina-

tion of the cps locus. The same fragment is contained in

the serotype 14 cps locus at a similar position, with the

addition of one base. A reversed sequence of the same

fragment is contained in the serotype 1/2 cps locus, which

results in IS630-Spn1 being changed into IS66-Spn1

transposase. The critical difference between the serotype 1

and 14 loci or the serotype 2 and 1/2 loci is a 906-bp

fragment containing IS transposase. The cps locus of the

four serotypes appears to have evolved from the same

ancestor. They could be stable binary transformants pro-

duced by homologous recombination.

Cross-absorption experiments showed that RS strepto-

cocci (S. suis serotype 1/2) contains an R antigen identi-

cal with that of R streptococci (S. suis serotype 2),

whereas the S component of RS streptococci, although

closely related, is not identical to the S antigen of S strep-

tococci (S. suis serotype 1) (Perch et al., 1981). According

to the comparison of the cps locus, the monosaccharide

composition and/or structure of serotype 1/2 CPS should

be similar to that of serotype 2, but different from that of

serotype 1. The cross-reaction between serotypes 1/2 and

1 may be caused by the similar antigenicity induced by

the CPS conformation or another component on the cell

surface. A one-way cross-reaction was detected between

serotypes 1 and 14. Serotype 1 strain can react with the

serum produced against both serotypes 1 and 14. Anti-

body activity against serotype 1 can be removed from

anti-serotype 14 serum by absorption with serotype 1

organisms. The adsorbed serum still can agglutinate with

serotype 14 strains (Gottschalk et al., 1989). Eight trans-

posases are absent in the serotype 1 cps locus compared

with serotype 14, which may lead to the production of

different CPS from the similar cps locus, resulting in the

one-way cross-reaction.

CPS synthesis pathway

The cps locus encodes the enzymes to build the repeat unit

(Garcia et al., 2000). According to the available cps locus

of all 15 serotypes, CPS of S. suis are generally synthesized

by the Wzy-dependent pathway, which is also found in

several other streptococcal species (Llull et al., 2001). The

CPS synthesis pathway of genetic groups 1 and 2 is a little

different. In genetic group 1, the capsule was predicted to

be amino-polysaccharide. The polysaccharide repeat unit

can be synthesized by the sequential transfer of monos-

accharides and adding some amino by aminotransferase

or utilizing amino-monosaccharide (serotype 9 and 10).

After the CPS is translocated across the bacterial mem-

brane, CapD-like protein generates amide bonds to anchor

CPS with the cell wall. In genetic group 2, CPS was pre-

dicted to be synthesized by transfer of an initial monosac-

charide phosphate to a membrane-associated lipid carrier,

followed by the sequential transfer of further monosaccha-

rides to produce the lipid-linked repeat unit.

Evolution of the cps locus

Several bacterial pathogens, including S. suis, exist in a

large number of antigenic variants because of differences

in the polysaccharides presented on the cell surface. The

evolution of the cps locus is very complex, with a long his-

tory of gene capture, loss and genetic rearrangements, and

it is probably unrealistic to expect to be able to untangle

their evolutionary history. A striking feature of the cps

locus is the presence of many highly divergent forms of

each of the key enzyme classes. There are 12 HGs for

polysaccharide polymerases, nine HGs for flippases, 38

HGs for GTs and a great diversity of transferases in the 15

serotype cps locus. There are also multiple kinds of trans-

posases (17 HGs) downstream of the locus. The G + C

content of the genomic DNA in S. suis (GenBank acces-

sion nos. AM946016, AAFA00000000, AARD00000000,

FM252031, FM252032, CP000407, CP000408, CP002465.1,

CP000837.1 and CP002633.1) is about 41%, which is

33.62–36.55 in the cps locus (Table 1). The presence of

multiple non-homologous or highly divergent forms of

key enzymes and horizontal mobile elements (transposas-

es), together with the lower percentage of G + C content

of the region, supports the view that these genes may have

been imported into S. suis (or their ancestors) on multiple

occasions from different and unknown sources.

An attempt was made to amplify the cps locus of other

serotypes by the PCR method. The amplicon between P1

and P2 can be generated. The type-specific region of the

other serotypes cannot be amplified by primers P3 and

P4 (P5 and P6). Perhaps their cps locus is too large to be

amplified by the DNA polymerases present. Because the

exact composition and structure of most S. suis serotypes

CPS is unknown, the real function of the genes was only

analyzed according to the similarity to other proteins and

motifs. The availability of the sequences of the 15 cps

locus and the analysis of their relatedness will provide the

basis to understand the CPS synthesis pathway and gene

evolution of the S. suis cps locus.

Acknowledgement

This work was supported by the Special Fund for Public

Welfare Industry of the Chinese Ministry of Agriculture

(200803016).


122 K. Wang et al.

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Supporting Information

Additional Supporting Information may be found in the

online version of this article:

Table S1. Homology groups including numbers of mem-

bers and product description.

Please note: Wiley-Blackwell is not responsible for the

content or functionality of any supporting materials sup-

plied by the authors. Any queries (other than missing

material) should be directed to the corresponding author

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124 K. Wang et al.

genetic analysis of the capsular polysaccharide synthesis locus in 15 streptococcus suis serotypes

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