Complete genome sequence of a novel infectious bronchitis virus strain circulating in China with a distinct S gene

An avian infectious bronchitis virus (IBV) was isolated and identified from a commercial layer flock vaccinated with live attenuated H120 vaccine in China, designed as ck/CH/IBTZ/2012. To determine the origination and evolution of this isolated strain, we have carried out a complete genome sequencing of this strain. The genome of the ck/CH/IBTZ/2012 strain is 27,691 nucleotides in length and includes more than 10 open reading frames. Sequence comparison and phylogenetic analysis based on the full-length genomic sequences showed that ck/CH/IBTZ/2012 is mostly related to the LX4-like strains. However, sequence analysis based on the spike protein (S) gene sequences revealed that ck/CH/IBTZ/2012 possesses a distinct S gene setting it apart from the Massachusetts-type strains and LX4-type strains. The cleavage site within the spike protein (S) of ck/CH/IBTZ/2012 is HRRKR, which is different from the majority of the IBVs in China for their cleavage sits are HRRRR. Recombination analysis showed that ck/CH/IBTZ/2012 is a chimeric virus with a LX4-like backbone except S gene which might be from an unknown strain. Based on the data presented in this paper, it can be concluded that genetic changes due to adaptive evolution and recombination both contributed to the origin of strain ck/CH/IBTZ/2012, which belongs to a new genotype.