Biology subjects

Hu, S. K.

Publications and source records attributed to Hu, S. K..

7 recordsLinked to original sources

bioRxiv2026

Riverine input and eddy edge effects on microeukaryotic biodiversity in the Northern Gulf

Marine microorganisms drive the biogeochemical processes that sustain ocean ecosystems, such as primary production, nutrient cycling, and the transfer of carbon and energy to higher trophic levels. Single-celled eukaryotic organisms (microbial eukaryotes or protists) represent a multifaceted group that contribute to food web dynamics as primary producers, consumers, parasites, and nutrient remineralizers. The Northern Gulf of Mexico is a productive, river-influenced, semi-enclosed ecosystem with strong economic ties. To gain detailed insight into Gulf-based microbial communities, we present an 18S rRNA gene metabarcoding survey across 12 stations from the Louisiana coast to offshore Northern Gulf encompassing the surface to over 2,000 m. Together, water mass, the ratio of dissolved inorganic carbon to total alkalinity, distance to the coast, and depth structured protistan species composition; a secondary signal was associated with the edge of a Loop Current eddy. At the Mississippi River-Gulf interface, diatoms dominated the upper water column depths, with dinoflagellates, parasitic Syndiniales, and rhizaria making up the majority of the offshore communities throughout the entire water column. Shifts in species composition with Northern Gulf environmental gradients reflect varied trophic strategies and have implications for carbon transfer efficiency and food web structure. These results establish a baseline characterization of microeukaryotic biodiversity across coastal-to-offshore and surface to deep-sea gradients that provide critical context for future assessments of Northern Gulf ecosystem resilience.

ecology↗

bioRxiv2023

Microbial eukaryotic predation pressure and biomass at deep-sea hydrothermal vents: Implications for deep-sea carbon cycling

Deep-sea hydrothermal vent geochemistry shapes the foundation of the microbial food web by fueling chemolithoautotrophic microbial activity. Microbial eukaryotes (or protists) play a critical role in hydrothermal vent food webs as consumers, hosts of symbiotic bacteria, and as a nutritional source to higher trophic levels. We measured cell abundances and predation pressures of vent-associated microbial eukaryotes in low temperature diffuse hydrothermal fluids at the Von Damm and Piccard vent fields along the Mid-Cayman Rise in the Western Caribbean Sea. We present findings from experiments performed under in situ pressure that show higher cell abundances and grazing rates compared to those done at 1 atmosphere (shipboard ambient pressure); this trend was attributed to the impact of depressurization on cell integrity. A relationship between protistan grazing rate, prey cell abundance, and temperature of end member hydrothermal vent fluid was observed at both vent fields, regardless of experimental approach. The quantification of protistan biomass and grazing pressure shows that hydrothermally-fueled microbial food webs play a significant role in the broader deep-sea carbon budget by contributing to local carbon export and supply of nutrient resources to the deep ocean.

microbiology↗

bioRxiv2023

Missing microbial eukaryotes and misleading meta-omic conclusions

Meta-omics has become commonplace in the study of microbial eukaryotes. The explosion of available data has inspired large-scale analyses, including species or taxonomic group distribution mapping, gene catalog construction, and inference on the functional roles and activities of microbial eukaryotes in situ. However, genome and transcriptome databases are prone to misannotation biases, and meta-omic inventories may have no recoverable taxonomic annotation for more than half of assembled contigs or predicted proteins. Direct mapping solely to organisms of interest might introduce a problematic misattribution bias, while full databases can annotate any cataloged organism but may be imbalanced between taxa. Here, we explore the potential pitfalls of common approaches to taxonomic annotation of protistan meta-omic datasets. We argue that ongoing curation of genetic resources is critical in accurately annotating protists in situ in meta-omic datasets. Moreover, we propose that precise taxonomic annotation of meta-omic data is a clustering problem rather than a feasible alignment problem. We show that taxonomic membership of sequence clusters demonstrates more accurate estimated community composition than returning exact sequence labels, and overlap between clusters can address database shortcomings. Clustering approaches can be applied to diverse environments while continuing to exploit the wealth of annotation data collated in databases, and database selection and evaluation is a critical part of correctly annotating protistan taxonomy in environmental datasets. We re-analyze three environmental datasets at three levels of taxonomic hierarchy in order to illustrate the critical importance of both database completeness and curation in enabling accurate environmental interpretation.

microbiology↗

bioRxiv2021

The high-throughput gene prediction of more than 1,700 eukaryote genomes using the software package EukMetaSanity

Gene prediction and annotation for eukaryotic genomes is challenging with large data demands and complex computational requirements. For most eukaryotes, genomes are recovered from specific target taxa. However, it is now feasible to reconstruct or sequence hundreds of metagenome-assembled genomes (MAGs) or single-amplified genomes directly from the environment. To meet this forth-coming wave of eukaryotic genome generation, we introduce EukMetaSanity, which combines state-of-the-art tools into three pipelines that have been specifically designed for extensive parallelization on high-performance computing infrastructure. EukMetaSanity performs an automated taxonomy search against a protein database of 1,482 species to identify phylogenetically compatible proteins to be used in downstream gene prediction. We present the results for intron, exon, and gene locus prediction for 112 genomes collected from NCBI, including fungi, plants, and animals, along with 1,669 MAGs and demonstrate that EukMetaSanity can provide reliable preliminary gene predictions for a single target taxon or at scale for hundreds of MAGs. EukMetaSanity is freely available at https://github.com/cjneely10/EukMetaSanity.

bioinformatics↗

bioRxiv2021

Eukaryotic genomes from a global metagenomic dataset illuminate trophic modes and biogeography of ocean plankton

Metagenomics is a powerful method for interpreting the ecological roles and physiological capabilities of mixed microbial communities. Yet, many tools for processing metagenomic data are not designed to consider eukaryotes, nor are they built for an increasing amount of sequence data. EukHeist is an automated pipeline to retrieve eukaryotic and prokaryotic metagenome assembled genomes (MAGs) from large-scale metagenomic datasets. We developed the EukHeist workflow to specifically process large amounts of both metagenomic and/or metatranscriptomic sequence data in an automated and reproducible fashion. Here, we applied EukHeist to the large-size fraction data (0.8-2000{micro}m) from Tara Oceans to recover both eukaryotic and prokaryotic MAGs, which we refer to as TOPAZ (Tara Oceans Particle-Associated MAGs). The TOPAZ MAGs consisted of >900 environmentally-relevant eukaryotic MAGs and >4,000 bacterial and archaeal MAGs. The bacterial and archaeal TOPAZ MAGs expand the known marine phylogenetic diversity through the increase in coverage of likely particle- and host-associated taxa. We also demonstrate an approach to infer the putative functional mode of the recovered eukaryotic MAGs. A global survey of the TOPAZ MAGs enabled the identification of ecological cohorts, driven by specific environmental factors, and putative host-microbe associations. ImportanceDespite the ecological importance of single-celled eukaryotic organisms in marine environments, the majority are difficult to cultivate in the lab. Sequencing genetic material extracted from environmental samples enables researchers to document naturally-occurring protistan communities. However, conventional sequencing methodologies cannot separate out the genomes of individual organisms. To more completely capture the entire genomic content of mixed protistan community, we can create bins of sequences that represent the same organism. We developed a pipeline that enables scientists to bin individual organisms out of metagenomic reads, and show results that provide exciting insights into what protistan communities are present in the ocean and what roles they play in the ecosystem. Here, a global survey of both eukaryotic and prokaryotic MAGs enabled the identification of ecological cohorts, driven by specific environmental factors, and putative host-microbe associations. Accessible and scalable computational tools, such as EukHeist, are likely to accelerate the identification of meaningful genetic signatures from large datasets, ultimately expanding the eukaryotic tree of life.

microbiology↗

bioRxiv2021

Diel population dynamics and mortality of Prochlorococcus in the North Pacific Subtropical Gyre

Photosynthesis fuels primary production at the base of marine food webs. Yet, in many surface ocean ecosystems, diel-driven primary production is tightly coupled to daily loss. This tight coupling raises the question: which top-down drivers predominate in maintaining persistently stable picocyanobacterial populations over longer time scales? Motivated by high-frequency surface water measurements taken in the North Pacific Subtropical Gyre (NPSG), we developed multitrophic models to investigate bottom-up and top-down mechanisms underlying the balanced control of Prochlorococcus populations. We find that incorporating photosynthetic growth with viral- and predator-induced mortality is sufficient to recapitulate daily oscillations of Prochlorococcus abundances with baseline community abundances. In doing so, we infer that grazers function as the primary top-down factor despite high standing viral particle densities while identifying the potential for light-dependent viral traits and non-canonical loss factors to shape the structure and function of marine microbial communities.

ecology↗

bioRxiv2021

Protistan grazing impacts microbial communities and carbon cycling at deep-sea hydrothermal vents

Microbial eukaryotes (or protists) in marine ecosystems are a link between microbial primary producers and all higher trophic levels. The rate at which heterotrophic protistan grazers consume microbial prey and recycle organic matter is an important factor that influences marine microbial food webs and carbon cycling. At deep-sea hydrothermal vents, chemosynthetic bacteria and archaea form the base of a food web that functions in the absence of sunlight, but the role of protistan grazers in these highly productive ecosystems is largely unexplored. Here, we pair grazing experiments with a molecular survey to quantify protistan grazing and to characterize the composition of vent-associated protists in low-temperature venting fluids from Gorda Ridge in the North East (NE) Pacific Ocean. Results reveal protists exert higher predation pressure at vents compared to the surrounding deep seawater environment and may account for consuming 28-62% of the daily stock of prokaryotic biomass within the hydrothermal vent food web. The vent-associated protistan community was more species rich relative to the background deep sea, and patterns in the distribution and co-occurrence of vent microbes provide additional insights into potential predator-prey interactions. Ciliates, followed by dinoflagellates, Syndiniales, rhizaria, and stramenopiles dominated the vent protist community and included bacterivorous species, species known to host symbionts, and parasites. Our findings provide an estimate of protistan grazing pressure within hydrothermal vent food webs, highlighting the role that diverse deep-sea protistan communities have in carbon cycling. SignificanceHeterotrophic protists are ubiquitous in all aquatic ecosystems and represent an important ecological link because they transfer organic carbon from primary producers to higher trophic levels. Here, we quantify the predator-prey trophic interaction among protistan grazers and microbial prey at multiple sites of hydrothermal venting near the Gorda Ridge spreading center in the NE Pacific Ocean. Grazing pressure was higher at the site of active diffuse flow and was carried out by a highly diverse assemblage of protistan species; elevated grazing rates are attributed to higher concentrations of chemosynthetic microorganisms and biological diversity localized to hydrothermal vent environments.

microbiology↗