Novel Divavirus (the family Betaflexiviridae) and Mitovirus (the family Narnaviridae) species identified in basil (Ocimum basilicum)

Transcriptome data obtained from a plant sample often contain a large number of reads that are derived from associated RNA virus genomes that were co-isolated during RNA preparation. These virus-derived reads can be assembled into a novel plant RNA genome sequence. Here, a basil (Ocimum basilicum) transcriptome dataset was analyzed to identify two new RNA viruses, which were named Ocimum basilicum RNA virus 1 (ObRV1) and Ocimum basilicum RNA virus 2 (ObRV2). A phylogenetic analysis of the ObRV1 RNA-dependent RNA polymerase (RdRp) motif indicated that ObRV1 is a novel species of the genus Divavirus of the family Betaflexiviridae. ObRV1 is the fourth divavirus species to be identified. The ObRV2 RdRp motif showed sequence similarity to viruses of the genus Mitovirus of the family Narnaviridae, which infect fungal mitochondria. Although most of the known mitoviruses do not produce a functional RdRp using the plant mitochondrial genetic code, the ObRV2 encodes a full-length RdRp using both the fungal and plant mitochondrial genetic codes.

Isolation of additional bacteriophages with genomes of segmented double-stranded RNA

Eight different bacteriophages were isolated from leaves of Pisum sativum, Phaseolus vulgaris, Lycopersicon esculentum, Daucus carota sativum, Raphanus sativum, and Ocimum basilicum. All contain three segments of double-stranded RNA and have genomic-segment sizes that are similar but not identical to those of previously described bacteriophage phi6. All appear to have lipid-containing membranes. The base sequences of some of the viruses are very similar but not identical to those of phi6. Three of the viruses have little or no base sequence identity to phi6. Two of the viruses, phi8 and phi12, contain proteins with a size distribution very different from that of phi6 and do not package genomic segments of phi6. Whereas phi6 attaches to host cells by means of a pilus, several of the new isolates attach directly to the outer membrane. Although the normal hosts of these viruses seem to be pseudomonads, those viruses that attach directly to the outer membrane can establish carrier states in Escherichia coli or Salmonella typhimurium. One of the isolates, phi8, can form plaques on heptoseless strains of S. typhimurium.