Genetic variability and phylogeny of Torque teno sus virus 1 (TTSuV1) and 2 (TTSuV2) based on complete genomes

Thirteen genomes of Torque teno sus virus 1 (TTSuV1) and 2 (TTSuV2) were obtained to examine the diversity and evolution of swine TTVs. Despite the low nucleotide identity reported, the genomic organization and transcriptional profiles of TTVs are similar. The nucleotide diversity for TTSuV1 was higher than TTSuV2, and the pattern of mutation among the ORFs was also different. Phylogenetic and genetic analyses support the proposed division of TTV into two species. TTSuV1 showed high levels of variability (>30%), with three different types (the third described for the first time) that may display a geographical structure. In contrast, TTSuV2 showed lower levels of variability (<15%), and no different types could be described. Larger values for the ratios of synonymous (dS) to non-synonymous (dN) base substitutions (dS/dN) were reported for the ORFs pointing to a certain level of selective constraint in TTV genomes.