Mixed infection by a partitivirus and a negative-sense RNA virus related to mymonaviruses in the polypore fungus Bondarzewia berkeleyi.

Virus communities of forest fungi remain poorly characterized. In this study, we detected two new viruses co-infecting an isolate of the polypore fungus Bondarzewia berkeleyi using high-throughput sequencing. One of them was a putative new partitivirus designated as Bondarzewia berkeleyi partitivirus 1 (BbPV1), with two linear dsRNA genome segments of 1928 and 1863 bp encoding a putative RNA-dependent RNA polymerase (RdRP) of 591 aa and a putative capsid protein of 538 aa. The other virus, designated as Bondarzewia berkeleyi negative-strand RNA virus 1 (BbNSRV1), had a non-segmented negative-sense RNA genome of 10,983 nt and was related to members of family Mymonaviridae. The BbNSRV1 genome includes six predicted open reading frames (ORFs) of 279, 425, 230, 174, 200 and 1970 aa. The longest ORF contained conserved regions corresponding to Mononegavirales RdRP and mRNA-capping enzyme region V constituting the mononegavirus Large protein. In addition, a low level of sequence identity was detected between the putative nucleocapsid protein-coding ORF2 of Lentinula edodes negative-strand RNA virus 1 and BbNSRV1. The viruses characterized in this study are the first ones described in Bondarzewia spp., and BbNSRV1 is the second mymona-like virus described in a basidiomycete host.