Biology subjects

Mars Brisbin, M.

Publications and source records attributed to Mars Brisbin, M..

10 recordsLinked to original sources

bioRxiv2026

Nutrient response strategies drive coastal range shifts of phytoplankton taxa

Coastal phytoplankton blooms are important drivers of regional and global marine primary production. Recently documented increases in coastal phytoplankton blooms in the first quarter of the 21st century may be a consequence in part of changing environmental conditions and have important ecological implications. Here, we explore coastal phytoplankton dynamics in Cape Cod Bay, MA, USA. We use a 20-year phytoplankton ecology dataset to identify potential drivers of the increasing prevalence of two regionally-rare phytoplankton taxa: a coccolithophore thought to thrive in the global open ocean, and a dinoflagellate genus with potentially toxic members. Using metatranscriptomics, we show that these minor phytoplankton taxa leverage unique strategies to gain a competitive advantage under nutrient limitation compared to traditionally dominant taxa and compared to a diatom taxon that became modestly more abundant over the study period. Our results highlight the ecological dynamics arising from long-term shifts in temperature and nutrient status in coastal ecosystems.

ecology↗

bioRxiv2025

B-vitamin requirements and phycosphere interactions for the HAB-forming dinoflagellate, Pyrodinium bahamense var. bahamense

Pyrodinium bahamense is a saxitoxin-producing dinoflagellate found in tropical and subtropical estuarine waters globally, with the var. bahamense variety forming recurrent harmful algal blooms (HABs) in Florida estuaries. The intensity and duration of bloom peaks in Florida estuaries vary interannually, but life cycle transitions, estuarine water residence time, water temperature, salinity, and nutrient concentrations appear to contribute to bloom formation. However, the impact of B-vitamin availability on P. bahamense bloom formation has not been investigated, despite the knowledge that many HAB dinoflagellates require B-vitamins for growth and bloom development. In this study, we determined that of the three B-vitamins most commonly required by marine phytoplankton--biotin (B7), thiamine (B1), and cobalamin (B12)--P. bahamense strictly requires an exogenous B12 source to sustain growth. As bacterial interactions can fulfill phytoplankton B12 requirements, we tested whether bacterial communities recruited from two Florida estuaries could rescue P. bahamense from B12 limitation. We demonstrate that bacteria from the Indian River Lagoon (IRL) estuary collected during a P. bahamense bloom restored P. bahamense growth in media missing B12, while bacteria present in Old Tampa Bay (OTB) water collected when P. bahamense was not present did not restore P. bahamense growth in media missing B12. Putative bacterial B12 producers exclusively recruited from IRL included Enterobacteraceae genera that likely have anthropogenic sources. Our findings suggest B12 is essential for fueling P. bahamense blooms, and that specific bacterial communities may contribute to bloom development through B12 production.

microbiology↗

bioRxiv2024

Urbanization of a subtropical island (Okinawa, Japan) alters physicochemical characteristics and disrupts microbial community dynamics in nearshore ecosystems

Subtropical and tropical islands are undergoing rapid urbanization as human populations and tourism expand worldwide. Urbanization disrupts coastal ecosystems by replacing forests and other natural habitats with roads, parking lots, and buildings. These impervious surfaces increase the amount of runoff and pollution that reaches coastal ecosystems. Urbanization also comes with increased industry, waste treatment needs, fishing and aquaculture pressure, and coastline engineering. Despite the major changes to coasts that accompany urbanization, specific impacts on marine ecosystems can be difficult to measure due to missing baselines. Here, we take advantage of a large gradient in urbanization on the subtropical island of Okinawa, Japan, to evaluate the impact of urbanization on nearshore ecosystems. We measured physicochemical parameters and assessed bacterial community composition every two weeks for one year at two nearshore sites adjacent to watersheds with >70% urban land use and two nearshore sites adjacent to watersheds with >70% rural land use. Our results show that urbanization increases freshwater input and nutrient loading to nearshore ecosystems and profoundly alters the microbial community, overriding the natural seasonal succession observed at rural sites. At urban sites, we detected multiple bacterial species that are fecal indicators and human or marine organism pathogens. The altered physicochemical conditions and microbial communities at urban sites can contribute to the degradation of nearby coral reefs. Results highlight the importance of a "ridge-to-reef" management mindset, as restoring natural coastlines could buffer the impact of urbanization on the marine environment.

ecology↗

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↗

bioRxiv2020

Cytoklepty in the plankton: a host strategy to optimize the bioenergetic machinery of endosymbiotic algae

Endosymbioses have shaped the evolutionary trajectory of life and remain widespread and ecologically important. Investigating modern oceanic photosymbioses can illuminate how algal endosymbionts are energetically exploited by their heterotrophic hosts, and inform on putative initial steps of plastid acquisition in eukaryotes. By combining 3D subcellular imaging with photophysiology, carbon flux imaging and transcriptomics, we show that cell division of algal endosymbionts (Phaeocystis) is blocked within hosts (Acantharia), and that their cellular architecture and bioenergetic machinery are radically altered. Transcriptional evidence indicates that a nutrient-independent mechanism prevents symbiont cell division and decouples nuclear and plastid division. As endosymbiont plastids proliferate, the volume of the photosynthetic machinery volume increases 100-fold in correlation with expansion of a reticular mitochondrial network in close proximity to plastids. Photosynthetic efficiency tends to increase with cell size and photon propagation modeling indicates that the networked mitochondrial architecture enhances light capture. This is accompanied by 150-fold higher carbon uptake and upregulation of genes involved in photosynthesis and carbon fixation, which, in conjunction with a ca.15-fold size increase of pyrenoids demonstrates enhanced primary production in symbiosis. NanoSIMS analysis revealed major carbon allocation to plastids and transfer to the host cell. Invagination of the symbiosome into endosymbionts to optimize metabolic exchanges is strong evidence that the algal metamorphosis is irreversible. Hosts therefore trigger and unambiguously benefit from major bioenergetic remodeling of symbiotic microalgae with important consequences for the oceanic carbon cycle. Unlike other photosymbioses, this interaction represents a so-called cytoklepty, which is a putative initial step towards plastid acquisition.

physiology↗

bioRxiv2020

Paired high-throughput, in-situ imaging and high-throughput sequencing illuminate acantharian abundance and vertical distribution

Acantharians are important contributors to surface primary production and to carbon flux to the deep sea, but are often underestimated because their delicate structures are destroyed by plankton nets or dissolved by preservatives. As a result, relatively little is known about acantharian biology, especially regarding their life cycles. Here, we take a paired approach, bringing together high-throughput, in-situ imaging and high-throughput sequencing, to investigate acantharian abundance, vertical distribution, and life-history in the western North Pacific. Observed concentrations of acantharian cells correlated well with sequence abundances from acantharians with known, recognizable morphologies, but not to sequences from those without known morphology (basal environmental clades). These results suggest basal clades may lack characteristic star-shaped skeletons or are much smaller than known acantharians. The decreased size-range of acantharians imaged at depth supports current hypotheses regarding asymbiotic acantharian life cycles: cysts or vegetative cells release reproductive swarmer cells at depth and juvenile cells grow as they ascend towards the surface. Moreover, sequencing data present the possibility that photosymbiotic acantharians also reproduce at depth, like their asymbiotic, encysting relatives, which is counter to previous hypotheses. Finally, in-situ imaging captured a new acantharian behavior that may be a previously undescribed predation strategy.

microbiology↗

bioRxiv2019

Extreme storm-induced run-off causes rapid, context-dependent shifts in nearshore subtropical bacterial communities

Climate change scenarios predict tropical cyclones will increase in both frequency and intensity, which will escalate the amount of terrestrial run-off and mechanical disruption affecting coastal ecosystems. Bacteria are key contributors to ecosystem functioning, but relatively little is known about how they respond to extreme storm events, particularly in nearshore subtropical regions. In this study, we combine field observations and mesocosm experiments to assess bacterial community dynamics and changes in physicochemical properties during early- and late-season tropical cyclones affecting Okinawa, Japan. Storms caused large and fast influxes of freshwater and terrestrial sediment--locally known as red soil pollution--and caused moderate increases of macronutrients--especially SiO2 and PO43-. We detected shifts in relative abundances of marine bacteria and the introduction of terrestrially-derived bacteria, including putative coral and human pathogens, during storm events. Soil input alone did not substantially affect marine bacterial communities in mesocosms, indicating that other components of run-off or other storm effects likely exert a larger influence on bacterial communities. The storm effects were short-lived and bacterial communities quickly recovered following both storm events. The early- and late-season storms caused different physicochemical and bacterial community changes, demonstrating the context-dependency of extreme storm responses in a subtropical coastal ecosystem.

microbiology↗

bioRxiv2019

The microbiome wants what it wants: microbial evolution overtakes experimental host-mediated indirect selection

Microbes ubiquitously inhabit animals and plants, often affecting their hosts phenotype. As a result, even in a constant genetic background, the hosts phenotype may evolve through indirect selection on the microbiome. Microbiome engineering offers a promising novel approach for attaining desired host traits but has been attempted only a few times. Building on the known role of the microbiome on development in fruit flies, we attempted to evolve earlier eclosing flies by selecting on microbes in the growth media. We carried out parallel evolution experiments in no- and high-sugar diets by transferring media associated with fast-developing fly lines over the course of four rounds of selection. In each round, we used sterile eggs from the same inbred population, and assayed fly mean eclosion times. Ultimately, flies eclosed seven to twelve hours earlier, depending on the diet, but selection had no effect. 16S sequencing showed that the microbiome did evolve, particularly in the no sugar diet, with an increase in alpha diversity over time. Thus, while microbiome evolution did affect host eclosion times, these effects were incidental. Instead, any experimentally enforced selection effects were swamped by independent microbial evolution. These results imply that selection on host phenotypes must be strong enough to overcome other selection pressures simultaneously operating on the microbiome. The independent evolutionary trajectories of the host and the microbiome may limit the extent to which indirect selection on the microbiome can ultimately affect host phenotype. Random-selection lines accounting for independent microbial evolution are essential for experimental microbiome engineering studies.

microbiology↗

bioRxiv2018

Differential gene expression supports a resource-intensive, defensive role for colony production in the bloom-forming haptophyte, Phaeocystis globosa

Phaeocystis globosa forms dense, monospecific blooms in temperate, northern waters. Blooms are usually dominated by the colonial morphotype--non-flagellated cells embedded in a secreted mucilaginous mass. Colonial Phaeocystis blooms significantly affect food-web structure and function and negatively impact fisheries and aquaculture, but factors initiating colony production remain enigmatic. Destructive P. globosa blooms have been reported in tropical and subtropical regions more recently and warm-water blooms could become more common with continued climate change and coastal eutrophication. We therefore assessed genetic pathways associated with colony production by investigating differential gene expression between colonial and solitary cells in a warm-water Phaeocystis globosa strain. Our results illustrate a transcriptional shift in colonial cells with most of the differentially expressed genes downregulated, supporting a reallocation of resources associated with colony production. Dimethylsulfide and acrylate production and pathogen interaction pathways were upregulated in colonial cells, suggesting a defensive role for colony production. We identify several protein kinase signaling pathways that may influence the transition between morphotypes, providing targets for future research into factors triggering colony production. This study provides novel insights into genetic mechanisms involved in Phaeocystis colony formation and provides new evidence supporting a defensive role for Phaeocystis colonies.

ecology↗

bioRxiv2018

Intra-host symbiont diversity and extended symbiont maintenance in photosymbiotic Acantharea (clade F)

Photosymbiotic protists contribute to surface primary production in low-nutrient, open-ocean ecosystems and constitute model systems for studying plastid acquisition via endosymbiosis. Little is known, however, about host-symbiont dynamics in these important relationships, and whether these symbioses constitute mutualisms is debated. In this study, we applied single-cell sequencing methods and advanced fluorescent microscopy to investigate host-symbiont dynamics in clade F acantharians, a major group of photosymbiotic protists in oligotrophic subtropical gyres. We amplified the 18S rRNA gene from single acantharian hosts and environmental samples to assess intra-host symbiont diversity and to determine whether intra-host symbiont community composition directly reflects the available symbiont community in the surrounding environment. Our results demonstrate that clade F acantharians simultaneously host multiple species from the haptophyte genera Phaeocystis and Chrysochromulina. The intra-host symbiont community composition was distinct from the external free-living symbiont community, suggesting that these acantharians maintain symbionts for extended periods of time. After selective staining of digestive organelles, fluorescent confocal microscopy showed that symbionts were not being systematically digested, which is consistent with extended symbiont maintenance within hosts. Extended maintenance within hosts may benefit symbionts through protection from grazing or viral lysis, and therefore dispersal, provided that symbionts retain reproductive capacity.

ecology↗