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Virus Research 176 (2013) 78– 82

Contents lists available at SciVerse ScienceDirect

Virus Research

j ourna l ho me p age : www.elsev ier .com/ locate /v i rusres

enetic characterization of VP1 gene of seven Sacbrood virus isolated from threerovinces in northern China during the years 2008–2012

a Mingxiaoa,∗, Yin Yannab, Xu Xiaoli a, Zhang Lina, Li Yongfeia, Luan Zhidonga

Department of Laboratory Animal Center, Liaoning Medical University, Jinzhou 121001, ChinaTongliao No. 2 People’s Hospital, Tongliao 028000, China

a r t i c l e i n f o

rticle history:eceived 16 January 2013eceived in revised form 27 April 2013ccepted 30 April 2013vailable online 28 May 2013

eywords:acbrood virusP1 geneolecular epidemiology

yping criteria

a b s t r a c t

The genetic diversity of seven northern China isolated Sacbrood virus strains (SBV) has been analyzed, andhypervariable regions of the VP1 gene of 7 SBV were sequenced and characterized, in order to obtain epi-demiological and immunological information, and to suggest typing criteria for SBV. Sequence analysisof hypervariable regions of the VP1 gene in the genome of these isolates revealed a sequence homol-ogy of 91.0–99.3% among all seven local SBV isolates from Apis cerana from China, with a similarity of93.3–100.0% in deduced amino acid sequences. These local isolates shared 87.4–92.8% sequence homol-ogy with six SBV reference strains in GenBank (including two SBV reference strains from Apis cerana fromChina), which represents a 91.8–97.6% similarity in deduced amino acid sequences. Genetic analysis alsoshowed that five SBV strains from Apis cerana from China had a 13-amino-acid deletion at amino acidpositions 287–299, and two SBV strains infecting the Korean honeybee had a 17-amino-acid deletion at

amino acid positions 284–300 in comparison with other SBV. Phylogenetic analysis revealed two majorgroups (AC genotype SBV infecting Apis cerana and AM genotype SBV infecting Apis mellifera). The ACgenotype could be further divided into subgroups. Based on the results of phylogenetic analysis, a simi-larity scan of SBV nucleotide sequences was carried out by using Simplot software and results in similarresults. Our results suggest possible typing criteria for SBV based on the phylogenetic tree and sequencehomology, and also that the virus has host specificity and regional variations.

© 2013 Elsevier B.V. All rights reserved.

Sacbrood virus (SBV) is a common virus that infects the honey-ee, and has been detected in almost all colonies throughout theorld (Allen and Ball, 1996; Ellis and Munn, 2005; Mingxiao et al.,

010; Kim Cuc et al., 2008). SBV primarily affects the brood of theoneybee and results in larval death (Ritter, 1996); it may also affecthe adult bee, but in this case obvious signs of disease are lackingAnderson and Gibbs, 1989; Bailey, 1969). Such bees may, how-ver, have a decreased lifespan (Bailey, 1969; Wang and Moller,970). Sacbrood infection occurs most frequently in spring, whenhe colony is growing most rapidly and large numbers of suscep-ible larvae and young adults are available (Bailey, 1969). The SBVnfecting Apis cerana from China was first described in Guangdongrovince, China in 1972, and reemerged in Liaoning Province China

n 2008 (Mingxiao et al., 2010), causing lethal disease in individualees or the collapse of entire colonies in epidemic outbreaks. TheBV infecting the Korean honeybee, Apis cerana, was first described

∗ Corresponding author at: Department of Laboratory Animal Center, Liaoningedical University, No. 40, Section 3, Songpo Road, Jinzhou 121001, Liaoning

rovince, China. Tel.: +86 04164673585/15941628738; fax: +86 04164673528.E-mail address: nnxx8@yahoo.com.cn (M. Mingxiao).

168-1702/$ – see front matter © 2013 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.virusres.2013.04.018

in Korea in 2008, and was later responsible for epidemics, especiallyserious in 2010 (Choe et al., 2012).

The complete genomic sequence of SBV-UK (GenBank acces-sion number: AF092924 for UK 1990, isolated from UK at 1990)was first determined by Ghosh et al. (1999). SBV from Apis ceranafrom China sequences were identified by Zhang et al. (2001) andMingxiao et al. (2011) (GenBank accession numbers: AF469603 forGZ 2002 and HM237361 for LNQY 2008, isolated from GuangzhouProvince China in 2002 and Qingyuan Liaoning Province China in2008, respectively). The complete genomic sequence of KoreanSBV (GenBank accession numbers: HQ322114 for Kor 2010 isolatedfrom Apis cerana from Korea in 2010, JQ390592 for Kor19 2011 andJQ390591 for Kor21 2011, isolated from Apis mellifera from Koreain 2011) was determined by Lee et al. (2010) and Choe et al. (2012).Sequence analysis indicates that the genome contains one largeopen reading frame (ORF), encoding three or four structural pro-teins. SBV from Apis cerana from China was predicted by Ming-Xiaoet al. (2011) to contain four major structural proteins, VP1, VP2, VP3

and VP4. The VP1 gene has the highest amino acid sequence vari-ation among different SBV strains, and contains the common andmajor epitope of SBV (Cheng, 2011). Changes in this protein may beresponsible for the diversity of SBV and changes in host specificity.

s Research 176 (2013) 78– 82 79

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ence

hom

olog

y

in

13

stra

ins

of

SBV

.

nti

ty

GZ

2000

HB

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2012

LNSZ

2011

JLC

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2011

LNB

X

2009

LNN

D

2010

LNQ

Y

2012

LNQ

Y

2008

Kor

19

2011

Kor

2010

Uk

1990

Kor

21

2011

97.1

92.9

92.8

92.3

92.1

92.0

92.1

92.2

93.4

93.2

88.4

88.1

92.0

91.9

91.2

91.1

91.2

91.3

91.2

92.5

92.3

87.5

87.0

12

99.9

91.2

91.1

91.2

91.3

91.2

92.2

92.3

88.8

88.3

91.1

91.0

91.3

91.2

91.1

92.1

92.2

88.7

88.2

99.0

99.2

99.0

99.2

91.7

91.3

87.5

88.0

99.3

99.2

99.5

91.7

91.1

87.5

88.0

99.3

99.4

91.6

91.2

87.4

88.1

99.3

91.7

91.3

87.7

87.8

91.6

91.2

87.6

88.1

1

99.2

89.3

88.6

89.2

88.7

90.5

M. Mingxiao et al. / Viru

Although there have been many reports on sequence analysisnd epidemic outbreaks of SBV (Allen and Ball, 1996; Ellis andunn, 2005; Mingxiao et al., 2010; Kim Cuc et al., 2008), there

ave been very few to date concerning the molecular epidemiologynd typing of SBV. In this paper, we describe the genetic diversityf the nucleotide sequence encoding the VP1 protein, in isolatesbtained from outbreaks in Chinese honeybee colonies in northernhina between 2008 and 2012, and in published SBV strains in Gen-ank. At the same time, typing criteria for SBV were suggested usinghylogenetic analysis, similarity plots and sequence homology.

VP1 gene of the seven SBV strain obtained from threerovinces in northern China (Liaoning Province, Jilin Province,ebei Province) in 2008–2012 has been sequenced and six refer-nce strains were download from GenBank. The length of the VP1ene in LNQY 2012 (GenBank accession number: JX854440, iso-ated from QingYuan in the East Liaoning Province China in 2012),LCC 2011(GenBank accession number: JX854437, isolated fromhangchun Jilin Province being close to the East Liaoning Provinceorder China in 2011), LNND 2011 (GenBank accession number:X854439, isolated from Nandian in the East Liaoning Provincehina in 2011), LNBX 2009 (GenBank accession number: JX854438,

solated from Benxi in the East Liaoning Province China in 2009)nd LNQY 2008 was 945 nucleotides; in GZ 2000 (GenBank acces-ion number: AF251124, isolated from Guangzhou Province Chinan 2000), GZ 2002, Kor21 2011, HBQHD 2012 (GenBank accessionumber: JX854436, isolated from Qinghuangdao Hebei Provinceeing close to the West Liaoning Province border China in 2012)andNSZ 2011 (GenBank accession number: JX854441, isolated fromuizhong in the West Liaoning Province China in 2011) it was 984ucleotides; in UK 1990, it was 981 nucleotides; and in Kor 2010nd Kor19 2011, VP1 was 933 nucleotides in length.

By using the ClustalW method in the MegAlign program (DNAtar Inc., Madison, WI, USA), Multiple sequence comparisonsevealed a sequence homology of 91.0–99.3% among all seven localBV isolates from three provinces in northern China (Table 1),ith a similarity of 93.3–100.0% in deduced amino acid sequences

Table 2). They also demonstrated that these SBV from Apis ceranarom China isolates had a closer genetic relationship to GZ 2000,Z 2002, Kor 2010 and Kor19 2011 (91.1–92.9%, with a similarityf 94.9–96.8% in deduced amino acid sequences) than to UK 1990nd Kor21 2011 (87.4–88.8%, with a similarity of 93.0–94.5% ineduced amino acid sequences) (Tables 1 and 2).

Multiple deduced amino acid sequence alignment showedhat the sequences of LNQY 2012, JLCC 2011, LNND 2011,NBX 2009 and LNQY 2008 were missing a 13-amino-acid sectionetween nucleotides 287 and 299 (present in GZ 2000, GZ 2002,or21 2011, HBQHD 2012 and LNSZ 2011) and were identical to

hat of SBV from Apis mellifera from Korea. Similar comparisonsith Kor 2010 and Kor19 2011 identified a 17-amino-acid dele-

ion at amino acid positions 284–300 (present in GZ 2000, GZ 2002,or21 2011, HBQHD 2012 and LNSZ 2011), and in UK 1990 a miss-

ng amino acid at position 284 (present in GZ 2000, GZ 2002,or21 2011, HBQHD 2012 and LNSZ 2011) (Fig. 1).

To assess the genetic relatedness among the SBV strains, a phy-ogenetic tree based on the SBV-VP1 nucleotide sequences wasonstructed by the neighbor-joining method (p = distances) andsing up to 1000 bootstrapping replicates in MEGA 5.0 softwareor all seven isolates and six SBV reference strains in GenBank. TheP1 tree (shown in Fig. 2) revealed two clusters, related to SBV

nfecting Apis cerana (named the AC genotype) and SBV infectingpis mellifera (named the AM genotype). The most recent isolatef the AM cluster for which sequence information was available

as collected in Korea in 2011. The AM cluster was distinctly sepa-

ate from the AC lineages as supported by a clade credibility valuef 100.0 (Fig. 2). The AC cluster was further subdivided into fouremporally divergent groups I, II, III and IV (Fig. 2). Ta

ble

1V

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ide

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2002

GZ

2000

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201

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1990

80 M. Mingxiao et al. / Virus Research 176 (2013) 78– 82

Fig. 1. Alignment of deduced amino acid sequences of the sequenced VP1 genes from 13 SBV strains.

Fig. 2. Phylogenetic analysis of VP1 nucleotide sequences of SBV isolates and related published sequences. Numbers on the nodes indicate clade credibility values. Sequencenames are in the following format: isolate area accession number year of collection. The tree reveals two clusters, the AC and AM genotypes. The AC genotype is furthersubdivided into four temporally divergent subgroups. The bar represents a genetic distance of 0.005.

Fig. 3. Similarity plot of the SBV-VP1 nucleotide sequences obtained in this study. Each colored line indicates a group of SBV strains. (For interpretation of the references tocolor in this figure legend, the reader is referred to the web version of the article.)

M. Mingxiao et al. / Virus Rese

Tab

le

2V

P1

ded

uce

d

amin

o

acid

sequ

ence

hom

olog

y

in

13

stra

ins

of

SBV

.

Perc

ent

iden

tity

GZ

2000

HB

QH

D

2012

LNSZ

2011

JLC

C

2011

LNB

X

2009

LNN

D

2010

LNQ

Y

2012

LNQ

Y

2008

Kor

19

2011

Kor

2010

Uk

1990

Kor

21

2011

GZ

2002

97.6

97.6

97.6

94.9

95.6

95.2

95.2

94.9

97.4

97.4

84.8

93.9

GZ

2000

95.7

95.7

93.3

94.0

93.7

93.7

93.3

95.8

95.8

93.0

91.8

HB

QH

D

2012

100

94.0

94.6

94.3

94.3

94.0

96.8

96.8

94.5

93.0

LNSZ

2011

94.0

94.6

94.3

94.3

94.0

96.8

96.8

94.5

93.0

JLC

C

2011

99.4

99.7

99.7

99.4

94.9

94.9

0 94

.0

93.7

LNB

X

2009

99.7

99.7

99.4

95.5

95.5

94.3

94.0

LNN

D

2010

100.

0

99.7

95.2

95.2

94.0

93.7

LNQ

Y

2012

99.7

95.2

95.2

94.0

93.7

LNQ

Y

2008

94.9

94.9

93.7

93.3

Kor

19

2011

100.

0

96.1

95.8

Kor

2010

96.1

95.8

Uk

1990

96.0

arch 176 (2013) 78– 82 81

Based on the results of phylogenetic analysis, the 13 SBV strainswere divided into five groups: A (GZ 2000 and GZ 2002); B(UK 1990 and Kor21 2011); C (Kor 2010 and Kor19 2011); D(HBQHD 2012 and LNSZ 2011); and E (LNQY 2012, JLCC 2011,LNND 2011, LNBX 2009 and LNQY 2008), for similarity analysis.Similarity plots were performed using Simplot software (Lole et al.,1999) with the following parameters: a window of 200 base pairs(bp; step: 20 bp), with gap-stripping and Kimura (two-parameter)correction, using groups A–D for FindSites, and group E as the querysequence. The Simplot similarity scan of nucleotide sequence pos-itions 642–881 in groups A–E revealed four well-separated groupsof SBV (Fig. 3). Groups A, B, C and D were most similar at position701, with 4.1%, 12.4%, 7.3% and 5.7% divergence, respectively, givena window size of 20 nucleotides. Group A was most divergent atposition 821 with 9.6% divergence, group B at position 881 with18.8% divergence, and groups C and D at position 841 with 11.3%and 15.5% divergence, respectively.

To compare the VP1 protein secondary structures, the structuralanalysis of the AC genotype of SBV was based on a comparisonof the translated amino acid consensus sequences from the GZ2002, Kor 2010, LNQY 2008 and LNSZ 2011 lineages, represent-

ing four different groups, using the Kyte and Doolittle algorithm(Kyte and Doolittle, 1982). This revealed four regions where therewere significant differences among the consensus sequences of theGZ 2002, Kor 2010, LNQY 2008 and LNSZ 2011 lineages. From thehydrophobicity plot, LNSZ 2011 seemed to represent the most dis-tinct lineage of the AC genotype (Fig. 4).

The incidence of SBV infection has increased considerably in pastfew years (Allen and Ball, 1996; Ellis and Munn, 2005; Mingxiaoet al., 2010; Kim Cuc et al., 2008), and the virus is seriously threaten-ing apiculture; however, the molecular epidemiology of SBV and itstyping criteria have not been published. Since it has been reportedthat the hypervariable region within VP1 has the highest amino acidsequence variation among different SBV strains (Mingxiao et al.,2011; Lee et al., 2010), the VP1 nucleotide sequences of seven SBVisolates obtained between 2008 and 2012 from parts of north-ern China (Liaoning Province, Jilin Province and Hebei Province,the latter two Provinces being close to the Liaoning border) weredetermined, and compared with published SBV strains.

The phylogenetic analysis (Figs. 1 and 2) and the similarity plot(Fig. 3) of SBV, including our collection of isolates and publishedSBV strains, confirms the presence of two independent lineages,the AC genotype of SBV infecting Apis cerana and the AM genotypeof SBV infecting Apis mellifera.

Although Kor21 2011 was isolated from the Korean honey-bee, Apis cerana, this strain formed a closely related cluster withUK 1990 and showed the highest sequence homology (90.5%). Wededuced that Kor21 2011 probably originated from SBV infectingApis mellifera, and then later infected Apis cerana. The Kor21 2011strain was therefore classified into the same group as UK 1990,the AM genotype. However, the nucleotide sequence of theKor21 2011strain was three nucleotides longer than that of SBV-UK, resulting in a deduced amino acid sequence that was one aminoacid longer.

The AC genotype could be further subdivided into fourtemporally divergent groups: I (GZ 2000 and GZ 2002); II(LNQY 2012, JLCC 2011, LNND 2011, LNBX 2009 and LNQY 2008);III (HBQHD 2012 and LNSZ 2011); and IV (Kor 2010 andKor19 2011). The sequence homologies were all more than 90%within the AC genotype, but less than 90% when compared withthe AM genotype, suggesting that sequence homology can be con-sidered as one of the typing criteria for SBV. Group I contained

isolates from outbreaks in 2008 and 2012 in central and easternLiaoning Province and in Changchun in Jinlin Province, Changchunbeing close to the eastern border of Liaoning Province. Groups II andIII consisted of isolates obtained from outbreaks in Guangzhou and

82 M. Mingxiao et al. / Virus Research 176 (2013) 78– 82

F es of

c reade

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osgSsmfcC

R

A

A

B

C

Wang, D.I., Moller, F.E., 1970. The division of labor and queen attendance behaviour

ig. 4. Amino acid hydrophobicity plot alignment based on the consensus sequencolored bars. (For interpretation of the references to color in this figure legend, the

orea, respectively. Group IV consisted of isolates obtained fromutbreaks in Sunzhong, Liaoning Province in 2011 and in Qinhuang-ao, Hebei Province in 2012. Sunzhong lies in western Liaoningrovince, close to the border with Hebei Province and Qinhuangdao.he results indicate that different subgroups of AC genotype existased on regional variations. Nevertheless, structural comparisonetween representative isolates from different subgroups of the ACenotype revealed no distinct differences, suggesting that the anti-enicity of the AC genotype of SBV has not changed. These findingsill be helpful for further research into the detection, prevention

nd cure of SBV.In conclusion, this study suggested typing criteria for SBV based

n the phylogenetic tree and sequence homology, with SBV-VP1equences showing homology of more than 90% belonging to sameenotype. The above typing criteria confirmed the presence of twoBV genotypes, namely the AC and AM genotypes. The study alsouggested that the differences between the AC and AM genotypesay be due to the virus adapting to a different host, and that dif-

erent subgroups of AC genotype exist based on regional variations,onfirming the conclusions made by Grabensteiner et al. (2001) andhoe et al. (2012).

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