Biology subjects

Ulloa, O.

Publications and source records attributed to Ulloa, O..

3 recordsLinked to original sources

bioRxiv2022

High genetic diversity in the pelagic deep-sea fauna of the Atacama Trench revealed by environmental DNA

A current paradigm in marine biodiversity states that faunal richness decreases with depth. However, the deep-ocean ecosystem has been significantly under-sampled, hindering a complete view of its biodiversity. This situation is accentuated in ultra-deep waters, where the remote and extreme conditions unfit the traditional sampling methods. Using environmental DNA, we assessed the pelagic metazoan diversity of the Atacama Trench from the high-productive near-surface level down to ~8000 m depth. Our results show that waters deeper than 4000 m contributed up to 50% of the overall genetic diversity. These findings contrast with similar observations in the less-productive Kermadec Trench, where the diversity in deep waters was lower than in shallower waters. Moreover, both deep pelagic ecosystems exhibited some unknown phylogenetic clades within the dominant taxonomic groups: hydrozoans and copepods. The deep-ocean biota may thus contribute to global biodiversity far more than hitherto suggested, especially in zones influenced by high primary production. Our results underline the need for increased effort to study these remote ecosystems and improve our understanding of their contribution to the ecology and biogeochemistry of the deep-sea pelagic and benthic realms.

ecology↗

bioRxiv2020

Flow cytometry with cell sorting and sequencing as a tool for the study of the Humboldt Current krill stomach microbiota

Euphausiids (or krill) are important contributors to marine biomass and key players in marine pelagic trophic webs. Euphausiids stomachs represent a specific niche for microbes that participate in the digestion of the host dietary components. To date, methods for the study of the diversity and function of these microorganisms remain complex. Often, bacterial ribosomal sequences obtained from lysates of stomachs are overrepresented by organisms from the surrounding environment. Flow cytometry with cell sorting (FC-CS) have become a powerful technique to study microbial community structure but also for the study of population genomics of gut-associated bacteria, even at a single-cell level. In this study, we used FC-CS and sequencing of the bacterial 16S rRNA gene to study the microorganisms inhabiting the stomach of the Humboldt Current krill, Euphausia mucronata. This approach was complemented with DNA extraction and sequencing from whole lysate stomachs as described for other crustacean species. Non-specific amplification was not retrieved in the polymerase chain reaction (PCR) from cells sorted, opposite to the observed using the DNA from the whole lysate. Sequences obtained from the whole stomach DNA were enriched in picocyanobacteria, meanwhile, sequences retrieved from cells sorted belonged almost exclusively to Balneola sp. of the new phylum, Balneolaeota. This study represents, to our knowledge, the first report of Balneola sp. in the stomach for any organism inhabiting the Humboldt Current System (HCS). Our results suggest that the stomach-associated microbiota can be characterized by FC-CS and sequencing by manual scraping of the stomach coupled with the DNA extraction and sequencing. This work represents a baseline for similar studies of other mesozooplankton groups. The implementation of this technique might complement future studies on host-microbes interaction and their implications on the marine pelagic food web.

microbiology↗

bioRxiv2020

Genome-resolved viral ecology in a marine oxygen minimum zone (OMZ)

Oxygen minimum zones (OMZs) are critical to marine nitrogen cycling and global climate change. While OMZ microbial communities are relatively well-studied, little is known about their viruses. Here we assess the viral community ecology of 22 deeply sequenced viral metagenomes along a gradient of surface oxygenated to anoxic waters (< 0.02 mol/L O2) in the Eastern Tropical South Pacific (ETSP) OMZ. We identified 46,127 viral populations (>5 kb), which augments the known viruses at this site by 10-fold. ETSP viral communities clustered into 6 groups that correspond to oceanographic features, with 3 clusters representing samples from suboxic to anoxic waters. Oxygen concentration was the predominant environmental feature driving viral community structure. Alpha and beta diversity of viral communities in the anoxic zone were lower than in surface waters, which parallels the low microbial diversity seen in other studies. Viruses were largely endemic as few (6% of viruses from this study) were found in at least another marine metagenome, and of those, most (77%) were restricted to other OMZs. Together these findings provide an ecological baseline for viral community structure, drivers and population variability in OMZs that will help future studies assess the role of viruses in these climate-critical environments. Originality-Significance StatementMarine oxygen minimum zones (OMZs) are unique and important ocean ecosystems where microbes drive climate-altering nutrient transformations. This study provides a baseline, deeply sequenced viral metagenomic dataset and reference viral genomes to assess ecological change and drivers across the oxygenated surface to de-oxygenated deep waters of the Eastern Tropical South Pacific (ETSP) OMZ. Community ecological assessment of the ETSP viromes reveals a relatively low diversity viral community with a high degree of endemic populations in the OMZ waters.

microbiology↗