VP2 gene based phylogenetic relationship of Indian isolates of Bluetongue virus serotype 1 and other serotypes from different parts of the world.

Bluetongue virus (BTV), a member of genus Orbivirus, family Reoviridae, is non-enveloped with double shelled structure and 10 segmented double stranded RNA genome. The RNA segment L2 encodes an outer capsid serotype specific viral protein VP2. BTV serotype 1 (BTV-1) specific novel primer pair, forward primer (1240-1271 bp) and reverse primer (1844-1813 bp), was designed using VP2 gene sequences available in GenBank to amplify 1240-1844 bp region because two hypervariable and three conserved regions have been reported within these 604 nucleotides. This primer pair successfully amplified cell culture adapted six Indian isolates of BTV-1. The 604 bp PCR product of VP2 gene of BTV-1 Avikanagar (A), Chennai (C) and Sirsa 3 (S3) Indian isolates were cloned in pPCR-Script Amp SK (+) vector and transformed into XL10-Gold Kan ultracompetent Epicurian coli cells. The positive clones selected by blue-white screening and colony touch PCR were sequenced. BTV-1A, C and S3 isolates revealed 99% nucleotide sequence identity within 1304-1844 bp region of VP2 gene. The partial VP2 gene sequences (1240-1844 bp region) revealed that BTV-1 Indian isolates were 89% identical with Australian (AUS) BTV-1 isolates while the identity with South African (SA) BTV-1 isolate was 75%. Phylogenetically, three BTV-1 Indian isolates formed one group which is closely related to BTV-1AUS isolates followed by BTV-1SA, BTV-2, 9, 23, 13, 17, 10 and 11 isolates from different parts of world. Based on partial VP2 gene sequences, it is concluded that Indian isolates of BTV-1 are closely related to BTV-1AUS isolates than BTV-1SA and other serotypes.