Mycelia-Assisted Isolation of Non-Host Bacteria Able to Co-Transport Phages.

Recent studies have demonstrated that phages can be co-transported with motile non-host bacteria, thereby enabling their invasion of biofilms and control of biofilm composition. Here, we developed a novel approach to isolate non-host bacteria able to co-transport phages from soil. It is based on the capability of phage-carrying non-host bacteria to move along mycelia out of soil and form colonies in plaques of their co-transported phages. The approach was tested using two model phages of differing surface hydrophobicity, i.e., hydrophobic Escherichia virus T4 (T4) and hydrophilic Pseudoalteromonas phage HS2 (HS2). The phages were mixed into soil and allowed to be transported by soil bacteria along the mycelia of Pythium ultimum. Five phage-carrying bacterial species were isolated (Viridibacillus sp., Enterobacter sp., Serratia sp., Bacillus sp., Janthinobacterium sp.). These bacteria exhibited phage adsorption efficiencies of ≈90-95% for hydrophobic T4 and 30-95% for hydrophilic HS2. The phage adsorption efficiency of Viridibacillus sp. was ≈95% for both phages and twofold higher than T4-or HS2-adsorption to their respective hosts, qualifying Viridibacillus sp. as a potential super carrier for phages. Our approach offers an effective and target-specific way to identify and isolate phage-carrying bacteria in natural and man-made environments.

A novel non-segmented double-stranded RNA virus from an Arctic isolate of Pythium polare.

We investigated virus infection in the oomycete Pythium polare from the Arctic. From 39 isolates investigated, 14 contained virus-like double-stranded RNA (dsRNA). Next generation sequencing revealed that the P. polare isolate OPU1176 contained three different virus-like sequences. We determined the full-length genome sequence of one of them. The 5397 nt-length genome had two overlapped open reading frames (ORFs) consistent with a toti and toti-like viruses, that we named Pythium polare RNA virus 1 (PpRV1). The ORF2 encoded an RNA-dependent RNA polymerase (RdRp). The shifty heptamer motif and RNA pseudoknot were predicted near the stop codon of ORF1, implying that the RdRp could be translated as a fusion protein with the ORF1 protein. Phylogenetic analysis with deduced RdRp amino acid sequences indicated that oomycete virus PpRV1 was closely related to the unclassified arthropod toti-like viruses. The comparison of PpRV1-free and -infected lines suggested that PpRV1 infected in a symptomless manner.

Genome sequence of a novel partitivirus identified from the oomycete Pythium nunn.

The mycoparasitic oomycete Pythium nunn isolate UZ415 contains two double-stranded RNAs (dsRNAs) of different sizes. The 1707-nt dsRNA1 and the 1475-nt dsRNA2 potentially encode an RNA-dependent RNA polymerase (RdRp) and a coat protein (CP), respectively, with sequence similarity to the RdRp and CP of gammapartitiviruses (< 57% and < 36%). Phylogenetic analysis of the deduced RdRp amino acid sequences indicated that the virus identified from P. nunn is classifiable as a distinct member of the genus Ganmmapartitivirus in the family Partitiviridae. This virus isolate is hereby named Pythium nunn virus 1 (PnV1).