Analysis of the entire genomes of fifteen torque teno midi virus variants classifiable into a third group of genus Anellovirus

Recently, we identified a novel human virus with a circular DNA genome of 3.2 kb, tentatively designated as torque teno midi virus (TTMDV), with a genomic organization resembling those of torque teno virus (TTV) of 3.8–3.9 kb and torque teno mini virus (TTMV) of 2.8–2.9 kb. To investigate the extent of genomic variability of TTMDV genomes, the full-length sequence was determined for 15 TTMDV isolates obtained from viremic individuals in Japan. The 15 TTMDV isolates comprised 3175–3230 bases and shared 67.0–90.3% identities with each other, and were only 68.4–73.0% identical to the 3 reported TTMDV isolates over the entire genome. TTMDV possessed a genomic organization with four open reading frames (ORF1–ORF4) with characteristic sequence motifs and stem and loop structures with high GC content, similar to TTV and TTMV. The total of 18 TTMDV genomes differed by up to 60.7% from each other in the amino acid sequence of ORF1 (658–677 amino acids), but segregated phylogenetically into the same cluster, which was distantly related to the TTVs and TTMVs. These results indicate that TTMDV with a circular DNA genome of 3.2 kb, has an extremely high degree of genomic variability, and is classifiable into a third group in the genus Anellovirus.