Saccharomyces paradoxus K66 Killer System Evidences Expanded Assortment of Helper and Satellite Viruses.

The Saccharomycetaceae yeast family recently became recognized for expanding of the repertoire of different dsRNA-based viruses, highlighting the need for understanding of their cross-dependence. We isolated the Saccharomyces paradoxus AML-15-66 killer strain from spontaneous fermentation of serviceberries and identified helper and satellite viruses of the family Totiviridae, which are responsible for the killing phenotype. The corresponding full dsRNA genomes of viruses have been cloned and sequenced. Sequence analysis of SpV-LA-66 identified it to be most similar to S. paradoxus LA-28 type viruses, while SpV-M66 was mostly similar to the SpV-M21 virus. Sequence and functional analysis revealed significant differences between the K66 and the K28 toxins. The structural organization of the K66 protein resembled those of the K1/K2 type toxins. The AML-15-66 strain possesses the most expressed killing property towards the K28 toxin-producing strain. A genetic screen performed on S. cerevisiae YKO library strains revealed 125 gene products important for the functioning of the S. paradoxus K66 toxin, with 85% of the discovered modulators shared with S. cerevisiae K2 or K1 toxins. Investigation of the K66 protein binding to cells and different polysaccharides implies the ß-1,6 glucans to be the primary receptors of S. paradoxus K66 toxin. For the first time, we demonstrated the coherent habitation of different types of helper and satellite viruses in a wild-type S. paradoxus strain.

Trichomonas vaginalis infection in symbiosis with Trichomonasvirus and Mycoplasma.

Trichomonas vaginalis is a protozoan with an extracellular obligatory parasitic lifestyle exclusively adapted to the human urogenital tract and responsible for nearly a quarter billion sexually transmitted infections worldwide each year. This review focuses on symbiotic Trichomonasvirus and mycoplasmas carried by the protozoan, their molecular features and their role in altering the human vaginal microbiome and the immunopathogenicity of the parasite. Improved diagnostics and larger clinical interventional studies are needed to confirm the causative role of protozoan symbionts in the variable clinical presentation of trichomoniasis and its morbid sequelae, including adverse reproductive outcome, susceptibility to viral infections and cancer.

Analysis of new isolates reveals new genome organization and a hypervariable region in infectious myonecrosis virus (IMNV).

Infectious myonecrosis virus (IMNV) has been the cause of many losses in shrimp farming since 2002, when the first myonecrosis outbreak was reported at Brazilian's northeast coast. Two additional genomes of Brazilian IMNV isolates collected in 2009 and 2013 were sequenced and analyzed in the present study. The sequencing revealed extra 643 bp and 22 bp, at 5' and 3' ends of IMNV genome respectively, confirming that its actual size is at least 8226 bp long. Considering these additional sequences in genome extremities, ORF1 can starts at nt 470, encoding a 1708 aa polyprotein. Computational predictions reveal two stem loops and two pseudoknots in the 5' end and a putative stem loop and a slippery motif located at 3' end, indicating that these regions can be involved in the start and termination of translation. Through a careful phylogenetic analysis, a higher genetic variability among Brazilian isolates could be observed, comparing with Indonesian IMNV isolates. It was also observed that the most variable region of IMNV genome is located in the first half of ORF1, coinciding with a region which probably encodes the capsid protrusions. The results presented here are a starting point to elucidate the viral's translational regulation and the mechanisms involved in virulence.

Identification and molecular characterization of a new nonsegmented double-stranded RNA virus isolated from Culex mosquitoes in Japan.

Two infectious agents were isolated from Culex species mosquitoes in Japan and were identified as distinct strains of a new RNA virus by a method for sequence-independent amplification of viral nucleic acids. The virus designated Omono River virus (OMRV) replicated in mosquito cells in which it produced a severe cytopathic effect. Icosahedral virus particles of approximately 40 nm in diameter were detected in the cytoplasm of infected cells. The OMRV genome was observed to consist of a nonsegmented, 7.6-kb double-stranded RNA (dsRNA) and contain two overlapping open reading frames (ORFs), namely ORF1 and ORF2. ORF1 was found to encode a putative dsRNA-binding protein, a major capsid protein, and other putative proteins, which might be generated by co- and/or post-translational processing of the ORF1 polyprotein precursor, and ORF2 was found to encode a putative RNA-dependent RNA polymerase (RdRp), which could be translated as a fusion with the ORF1 product by a -1 ribosomal frameshift. Phylogenetic analysis based on RdRp revealed that OMRV is closely related to penaeid shrimp infectious myonecrosis virus and Drosophila totivirus, which are tentatively assigned to the family Totiviridae. These results indicated that OMRV is a new member of the family of nonsegmented dsRNA viruses infecting arthropod hosts, but not fungal or protozoan hosts.