Highly divergent mesnidoviruses found in TSA database, especially in spiders

The mesnidoviruses are positive single-stranded viruses belonging to the orderNidovirales. They were mostly found in mosquitoes, and represent a link from small to large nidoviruses. In this study, we report 18 newly discovered nidoviruses in TSA database, most of them are from spiders (OrderArachnida). After reassembly, we got 9 nearly complete genomes with sizes ranged from ∼19,500 to 33,500 nt. Further phylogenetic analyses assigned these nidoviruses toMesnidovirineae. Among them, the spider viruses represent a new clade. Pairwise evolutionary distance (PED) analysis showed these mesnidoviruses are highly divergent, with PED values from 2.2 to 4.9 with existing ones. Even among themselves the PED values are notable: with most exceeding the threshold of 0.32 that defines a new virus genus, suggesting these viruses are new species or belong to new higher-ranking taxa. In summary, we reported 18 mesnidoviruses in spiders, insects, plant andAnthozoa, the highly divergence suggested that spiders may harbor diverse mesnidoviruses. As the first nidovirus reported inArachnidaandAnthozoa, this discovery will contribute to the evolution study ofNidovirales.