Sequence analysis reveals mosaic genome of Aichi virus
© Han et al; licensee BioMed Central Ltd. 2011
Received: 23 May 2011
Accepted: 5 August 2011
Published: 5 August 2011
Aichi virus is a positive-sense and single-stranded RNA virus, which demonstrated to be related to diarrhea of Children. In the present study, phylogenetic and recombination analysis based on the Aichi virus complete genomes available in GenBank reveal a mosaic genome sequence [GenBank: FJ890523], of which the nt 261-852 region (the nt position was based on the aligned sequence file) shows close relationship with AB010145/Japan with 97.9% sequence identity, while the other genomic regions show close relationship with AY747174/German with 90.1% sequence identity. Our results will provide valuable hints for future research on Aichi virus diversity.
Aichi virus is a member of the Kobuvirus genus of the Picornaviridae family [1, 2] and belongs to a positive-sense and single-stranded RNA virus. Its presence in fecal specimens of children suffering from diarrhea has been demonstrated in several Asian countries [[3–6]], in Brazil and German , in France  and in Tunisia . Some reports showed the high level of seroprevalence in adults [7, 10], suggesting the widespread exposure to Aichi virus during childhood.
The genome of Aichi virus contains 8,280 nucleotides and a poly(A) tail. The single large open reading frame (nt 713-8014 according to the strain AB010145) encodes a polyprotein of 2,432 amino acids that is cleaved into the typical picornavirus structural proteins VP0, VP3, VP1, and nonstructural proteins 2A, 2B, 2C, 3A, 3B, 3C and 3D [2, 11]. Based on the phylogenetic analysis of 519-bp sequences at the 3C-3D (3CD) junction, Aichi viruses can be divided into two genotypes A and B with approximately 90% sequence homology . Although only six complete genomes of Aichi virus were deposited in GenBank at present, mosaic genomes can be found in strains from different countries.
The study sequences comprised six available complete genome sequences of Aichi virus from GenBank dated May 2011, including three Japan strains [GenBank: FJ890523, GenBank: NC_001918, GenBank: AB010145], one German strain [GenBank: AY747174], one Brazil strain [GenBank: DQ028632] and one China strain [GenBank: FJ890523]. Sequences were firstly screened to exclude patented and artificial mutants, and then aligned in the ClustalW program . The alignment was manually adjusted for the correct reading frame. Sequences showing less than 1% divergence from each other were considered as the same. The remaining five genomes include two Japan strains, one German strain, one Brazil strain and one China strain.
Phylogenetic Analysis and Recombination Detection
Before phylogenetic analysis, multiple-alignment was performed in the ClustalW program (http://www.clustal.org/). Phylogenetic trees were constructed using the neighbor-joining method and evaluated using the interior branch test method with Mega 4 software . Percent bootstrap support was indicated at each node. GenBank accession no. was indicated at each branch. Detection of potential recombinant sequences, identification of potential parental sequences, and localization of possible recombination break points were determined using the Recombination Detection Program (RDP), GENECONV , BOOTSCAN , MaxChi , CHIMAERA , and SISCAN  methods embedded in RDP3 . A Multiple-comparison-corrected P-value cutoff of 0.05 was used throughout.
Results and Discussion
Due to the limited numbers of Aichi virus sequence available at present days, the parental strains of the mosaic Aichi virus strain have not been identified in the present study. However, we think with the increasing number of Aichi virus genome, further study should be performed to elucidate whether accurate recombination event can happen between different Aichi virus strains. Because recombination is a relatively common phenomenon in positive-sense RNA viruses [[22–24]] and understanding recombination can be helpful in unravelling the evolution of pathogens and drug resistance.
Taken together, this study reveals a mosaic genome sequence of Aichi virus [GenBank: FJ890523], of which the nt 261-852 region shows close relationship with strain of AB010145/Japan, while the other genomic regions show close relationship with German strain [GenBank:AY747174].
This work was supported by the Professional Research Foundation for Advanced Talents of Jiangsu University under Grant No.10JDG059.
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