Molecular characterization of a novel bat-associated circovirus with a poly-T tract in the 3′ intergenic region

The family Circoviridae comprises a large group of small circular single-stranded DNA viruses with several members causing severe pig and poultry diseases. In recent years the number of new viruses within the family has had an explosive increase showing a high level of genetic diversity and a broad host range. In this report we describe two more circoviruses identified from bats in Yunnan and Heilongjiang provinces in China. Full genome sequencing has revealed that these bat associated circoviruses (bat ACV) should be classified as new species within the genus Circovirus based on the demarcation criteria of the International Committee on the Taxonomy of Viruses (ICTV). The most striking result is the novel finding of a 21-28 nt polythymidine (poly-T) tract in the 3′ terminal intergenic region of bat ACV isolates from Heilongjiang province. To understand its role in viral replication, a wild type bat ACV and a mutated version with the entire poly-T deleted were rescued through construction of infectious clones. Replication comparison in vitro showed that the poly-T is not essential for viral replication. Identification of additional bat ACV isolates and study of their biological characteristics will be the main task in future to understand the potential roles of bats in transmission of circoviruses to terrestrial mammals and humans.