ABSTRACTMicrobial consortia confer important benefits to animal and plant hosts, and model associations are necessary to examine these types of host/microbe interactions. The accessory nidamental gland (ANG) is a female reproductive organ found among cephalopod mollusks that contains a consortium of bacteria, the exact function of which is unknown. To begin to understand the role of this organ, the bacterial consortium was characterized in the Hawaiian bobtail squid,Euprymna scolopes, a well-studied model organism for symbiosis research. Transmission electron microscopy (TEM) analysis of the ANG revealed dense bacterial assemblages of rod- and coccus-shaped cells segregated by morphology into separate, epithelium-lined tubules. The host epithelium was morphologically heterogeneous, containing ciliated and nonciliated cells with various brush border thicknesses. Hemocytes of the host's innate immune system were also found in close proximity to the bacteria within the tubules. A census of 16S rRNA genes suggested thatRhodobacterales, Rhizobiales, andVerrucomicrobiabacteria were prevalent, with members of the genusPhaeobacterdominating the consortium. Analysis of 454-shotgun sequencing data confirmed the presence of members of these taxa and revealed members of a fourth,Flavobacteriaof theBacteroidetesphylum. 16S rRNA fluorescentin situhybridization (FISH) revealed that many ANG tubules were dominated by members of specific taxa, namely,Rhodobacterales,Verrucomicrobia, orCytophaga-Flavobacteria-Bacteroidetes, suggesting symbiont partitioning to specific host tubules. In addition, FISH revealed that bacteria, includingPhaeobacterspecies from the ANG, are likely deposited into the jelly coat of freshly laid eggs. This report establishes the ANG of the invertebrateE. scolopesas a model to examine interactions between a bacterial consortium and its host.

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.

We used a metagenomic approach to identify viruses that may be involved in the ecology of Daphnia spp. in Oneida and Cayuga lakes (upstate New York). We identified several highly represented, putative eukaryotic, circular, single-stranded deoxyribonucleic acid (DNA) viral genomes. Among these, we discovered a genotype similar in both sequence and genomic architecture to a virus previously reported from a hyperthermal lake that shares characteristics of both single-stranded ribonucleic acid (RNA) and single-stranded DNA viruses. We used quantitative polymerase chain reactions to study the prevalence and viral load of both positive-sense and negative-sense strands of the Daphnia mendotae-associated (Cladocera) hybrid virus (DMClaHV) over a summer season in Oneida and Cayuga lakes. DMClaHV had high prevalence within Daphnia populations, where viral load and the proportion of virus-positive individuals were higher preceding host population decline. DMClaHV viral load was different between two species of Daphnia (D. mendotae and D. retrocurva), and the dynamics between viruses and their hosts varied between the two lakes. We detected DMClaHV in eggs (ephippia) retrieved from Oneida Lake sediments with an estimated age of 30 yr. Using transmission electron microscopy, we observed small (20 nm diameter) virus-like particles in Daphnia that were well away from gut tissues and not associated with intracellular parasites. Because Daphnia plays a critical role in many lake ecosystems, DMClaHV may have important effects on herbivory and thus carbon flow through the lake ecosystem.

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