ABSTRACTAquatic viruses play important roles in the biogeochemistry and ecology of lacustrine ecosystems; however, their composition, dynamics, and interactions with viruses of terrestrial origin are less extensively studied. We used a viral shotgun metagenomic approach to elucidate candidate autochthonous (i.e., produced within the lake) and allochthonous (i.e., washed in from other habitats) viral genotypes for a comparative study of their dynamics in lake waters. Based on shotgun metagenomes prepared from catchment soil and freshwater samples from two contrasting lakes (Cayuga Lake and Fayetteville Green Lake), we selected two putatively autochthonous viral genotypes (phycodnaviruses likely infecting algae and cyanomyoviruses likely infecting picocyanobacteria) and two putatively allochthonous viral genotypes (geminiviruses likely infecting terrestrial plants and circoviruses infecting unknown hosts but common in soil libraries) for analysis by genotype-specific quantitative PCR (TaqMan) applied to DNAs from viruses in the viral size fraction of lake plankton, i.e., 0.2 μm > virus > 0.02 μm. The abundance of autochthonous genotypes largely reflected expected host abundance, while the abundance of allochthonous genotypes corresponded with rainfall and storm events in the respective catchments, suggesting that viruses with these genotypes may have been transported to the lake in runoff. The decay rates of allochthonous and autochthonous genotypes, assessed in incubations where all potential hosts were killed, were generally lower (0.13 to 1.50% h−1) than those reported for marine virioplankton but similar to those for freshwater virioplankton. Both allochthonous and autochthonous viral genotypes were detected at higher concentrations in subsurface sediments than at the water-sediment interface. Our data indicate that putatively allochthonous viruses are present in lake plankton and sediments, where their temporal dynamics reflect active transport to the lake during hydrological events and then decay once there.

Echinoderms are important constituents of marine ecosystems, where they may influence the recruitment success of benthic flora and fauna, and are important consumers of detritus and plant materials. There are currently no described viruses of echinoderms. We used a viral metagenomic approach to examine viral consortia within three urchins -Colobocentrotus atratus, Tripneustes gratilla and Echinometra mathaei -which are common constituents of reef communities in the Hawaiian archipelago. Metagenomic libraries revealed the presence of bacteriophages and densoviruses (family Parvoviridae) in tissues of all three urchins. Densoviruses are known typically to infect terrestrial and aquatic arthropods. Urchin-associated densoviruses were detected by quantitative PCR in all tissues tested, and were also detected in filtered suspended matter (.0.2 mm) from plankton and in sediments at several locations near to where the urchins were collected for metagenomic analysis. To the best of our knowledge, this is the first report of echinoderm-associated viruses, which extends the known host range of parvoviruses.

No abstract

Circular replication initiator protein (rep)-encoding ssDNA (CRESS-DNA) viruses have been widely reported in viral metagenomic surveys and in association with invertebrate zooplankton in freshwater and marine habitats. However, there have been no systematic or quantitative studies of their distribution in marine waters. We investigated the distribution of CRESS-DNA viruses in net plankton (> 64 µm) collected from geographically widespread locations, using quantitative PCR that targets viral genotypes previously recovered from soil, freshwater and estuarine free-living viruses, and viruses associated with arthropod tissues. We detected CRESS-DNA viruses in most net plankton samples except for a sample containing only the cyanobacterium Trichodesmium. Soil and freshwater plankton CRESS-DNA viruses were detected only at sites with substantial freshwater and runoff effects, while 2 CRESS-DNA viruses recovered from plankton of the Chesapeake Bay were detected in most net plankton tested. CRESS-DNA viruses recovered from marine copepods, the freshwater cladoceran Daphnia and the freshwater amphipod Diporeia were primarily detected in habitats where similar hosts were observed in zooplankton counts. Our data suggest that CRESS-DNA viruses previously recovered from invertebrate tissues and from virioplankton may be widely distributed in plankton > 64 µm, providing evidence for a zooplankton origin of this viral group.