Biology subjects

Bertrand, E. M.

Publications and source records attributed to Bertrand, E. M..

10 recordsLinked to original sources

bioRxiv2026

Glacier-induced upwelling shapes microbial communities in Arctic marine systems

The Canadian Arctic Archipelago (CAA) is warming at an unprecedented rate, leading to sea ice loss and glacial retreat. Marine-terminating (tidewater) glaciers can fuel summertime marine productivity by delivering nutrient-rich deep waters via upwelling to the surface ocean. While the impact of glacier-induced upwelling has been well-studied in the context of phytoplankton and primary productivity, its effects on broader marine microbial communities remain poorly understood. We investigated how glacier-driven upwelling shapes marine microbial (bacterial and archaeal) communities across a series of sites in the CAA. At upwelling sites, the upper 50 m of the water column exhibited elevated nutrient concentrations and physical characteristics that resembled deeper waters, which were associated with differences in microbial community composition relative to non-upwelling sites. Our results indicate that upwelling influences microbial communities in surface waters in two ways. It directly introduces typically deeper-water-associated taxa into surface waters and reshapes ecological niches by enhancing nutrient supply and stimulating primary production, indirectly driving changes in microbial communities. The enrichment of Candidatus Nitrosopumilus, a deep water nitrifier, likely affects nitrogen cycling and raises the possibility of active nitrification in surface waters. Likewise, the increased abundance of taxa known to be associated with phytoplankton-derived organic matter in upwelling regions suggests an enhanced capacity to process organic matter generated from elevated primary productivity. Ultimately, as tidewater glaciers continue to retreat, the resulting changes in the glacially-driven upwelling regime will likely shift marine microbial communities towards assemblages adapted to less productive ecosystems, with implications for nutrient cycling in these systems. ImportanceClimate change has a disproportionate impact on the Arctic, with rising temperatures causing increased marine-terminating glacier retreat and changes in the marine water column structure. The consequent loss of the ability of these glaciers to upwell deep water to the surface ocean results in a reduction of nutrient delivery and mixing in these ecosystems. Previous work has highlighted the importance of marine-terminating glaciers in sustaining phytoplankton productivity during the summer season through this delivery of deep-water nutrients to the surface ocean. The impact of glacially-induced upwelling on marine bacterial and archaeal communities, however, remains underexplored. We found that in regions with glacially-driven upwelling, the surface ocean showed enrichment of phytoplankton-associated taxa and nitrifiers commonly associated with deep waters. This work underscores the role of glacially-driven upwelling in structuring both microbial communities and nutrient cycling, suggesting that glacier loss could reshape community composition and biogeochemical processes in a rapidly changing Arctic.

microbiology↗

bioRxiv2026

Novel connections between B-vitamins and microbial communities along biogeochemical gradients in a large temperate estuary

As B-vitamins are organic cofactors required by prokaryotic and eukaryotic planktonic cells, their availability impacts aquatic microbial communities and associated biogeochemistry. Contrary to inorganic nutrients, measurements of B-vitamins from brackish systems are scarce and relationships between B-vitamins and plankton composition in estuaries are unclear, limiting our understanding of estuary biology in general as well as how B-vitamins are distributed and dispersed in marine systems. Here, we quantify multiple B-vitamins and their vitamers in particulate and dissolved phases, and characterize microbial community composition, across fresh to polyhaline zones of the Neuse River Estuary (NRE), North Carolina, USA. We uncover elevated concentrations of B-vitamins within the mid-estuary, Chlorophyll a maximum along with a unique suite of dissolved B-vitamin associated with sporadic surges in pico- and microplankton populations. The dynamics of both dissolved and particulate B-vitamin concentrations in space and time were striking - from subpicomolar to high picomolar levels observed and strong short-term (weeks) variability. We find notable autochtonous B-vitamin production in the estuary, but we expect the ability of the system to deliver these micronutrients to the ocean will depend on flushing as well as changes in microbial community. We identify vitamin B1, B12, psB12 (pseudocobalamin), and B3 as key explanatory variables for change in prokaryotic and eukaryotic NRE plankton, providing new evidence of B-vitamin influence upon estuarine plankton community composition. Our work reveals new complexities in B-vitamin production and consumption within zones of estuaries while underscoring these micronutrients as key drivers of microbial plankton composition.

ecology↗

bioRxiv2026

Thalassolituus haligoni sp. nov., BB40, a model species for non-cyanobacterial diazotrophs within Oceanospirillales isolated from a Fjord-like Inlet in Kjipuktuk

Marine non-cyanobacterial diazotrophs (NCDs) are recognized as globally distributed, however, few representatives have been isolated in pure cultures. As a result, understanding the physiology, growth rate, substrate preference and dinitrogen (N2) fixation capabilities proves difficult. Thalassolituus haligoni. sp. nov., BB40 was isolated from a fjord-like inlet within Kjipuktuk (Halifax), Nova Scotia. The fully sequenced genome displayed all necessary genes required for N2 fixation, and various carbon uptake pathways. The gram-negative flagellated rod shape bacterium displayed significantly higher growth rates in medium amended with nitrate (NO3-) or ammonia (NH3), compared to dissolved N2, as the sole nitrogen source. Biological N2 fixation rates were detectable across all conditions, measuring a range from 9.34 x 10-6 to 1.4 x 10-1 fmol N cell-1 day-1. Growth of the isolate was successful between 4 {degrees}C up to 35 {degrees}C, with a Topt of 20 {degrees}C for N2, and between 27 - 30 {degrees}C for fixed nitrogen (NO3- and NH3). The closest relatives to T. haligoni, were found to be the uncultured Arc-gamma-03 (99% average nucleotide identity (ANI)) and Oceanobacter antarcticus (81% ANI). T. haligoni also displays versatile capabilities for growth on various carbon, and nitrogen sources, and antibiotics. Collectively this study provides an in-depth physiological assessment of an Oceanospirillales diazotrophic species which we presently have limited knowledge of.

ecology↗

bioRxiv2025

Elemental allocation to molecular drivers of biogeochemistry in the Southern Ocean

Metabolic processes underpinning ocean biogeochemistry are powered by molecular machines, proteins, that require various elements to function. Yet, the allocation of elements to these proteins, and subsequent implications for biogeochemical processes, remain poorly characterized. Here we integrate elemental measurements with metaproteomics to quantitatively examine elemental use in Southern Ocean microbial proteins and metabolic processes. We demonstrate that iron availability influences elemental allocation, including decreased iron allocation to photosynthesis and compensatory incorporation of non-iron metals into metalloproteins under iron scarcity. Manganese was primarily allocated to photosynthesis in iron-replete conditions, and reallocated to other metabolic roles under low iron. Photosystem I:II protein mass ratios impacted both iron and manganese allocation, and appeared to be driven by iron availability. Approximately half of biogenic copper was found in plastocyanin, likely substituting for iron-containing cytochromes in photosynthesis. Moreover, biogenic nitrogen to phosphorus ratios were decoupled from ribosomal abundance, contrary to prevailing assumptions about ribosomal influence on stoichiometric regulation in the ocean. Instead, our results suggest that community composition and intracellular storage are important regulators of N:P in the Southern Ocean. Together, our findings identify key molecular mechanisms that modulate elemental demand and limitation, and provide a foundation for quantitatively connecting molecular measurements with biogeochemical models.

microbiology↗

bioRxiv2025

Superoxide dismutases shape manganese stoichiometry in Southern Ocean diatoms

Elemental stoichiometry of biomass is a focal point that connects different biogeochemical cycles. Yet, the mechanistic underpinnings of elemental stoichiometry are poorly quantified in many cases. We combined targeted and untargeted metaproteomics, Bayesian statistical modelling, and geochemical measurements to quantify the contribution of specific proteins to metal stoichiometry in natural populations of Southern Ocean diatoms. Our analyses indicate that a substantial amount of non-photosynthetic manganese (Mn) in diatoms in an Antarctic polynya can be attributed to superoxide dismutases ([~]0.7 {micro}mol Mn: mol Carbon; [~]20% of the total cellular Mn quota). We then used cultures and proteomic profiling of the key polar diatom Fragilariopsis cylindrus to identify environmental controls on superoxide dismutases, and discovered that iron concentration has little influence on the abundance of two Mn superoxide dismutases, while Mn limitation induces the depletion of these Mn superoxide dismutases and an accompanying increase of nickel superoxide dismutase. Overall, we combined metaproteomic approaches to quantify proteomic composition and connected these measurements to metal-to-carbon ratios and their responses to metal availability. Because metal quotas are key parameters in some biogeochemical models, our approach provides a direct mechanism for informing ecosystem-scale models with molecular measurements.

microbiology↗

bioRxiv2024

Production of the cobalamin lower ligand, 5,6-dimethylbenzimidazole, by a diatom under cobalamin-deplete conditions

Cobalamin, or vitamin B12, is a micronutrient required by half of all surveyed phytoplankton but produced only by select bacteria and archaea. Cobalamin influences community composition and primary productivity in various regions of the ocean and has been shown to be a critical currency in microbial interactions. Many marine microorganisms can salvage cobinamide and remodel pseudocobalamin, to generate cobalamin using the lower ligand 5,6-dimethylbenzimidazole (DMB), or the ribosylated form, -ribazole. The sources of the cobalamin lower ligand and intermediate remain poorly characterized but are currently attributed to prokaryotes alone. Here, we grew axenic cultures of a recently isolated Thalassiosiraceae diatom over a range of cobalamin concentrations (0, 0.75, 10, 100 pM). Then, using mass spectrometry, we quantified cobalamin and -ribazole in both particulate (cellular) and dissolved (media) phases. We found that this diatom is a facultative cobalamin consumer: it takes up cobalamin when available but can survive in its absence. Strikingly, under low cobalamin availability, we demonstrate that the diatom produces -ribazole. This highlights eukaryotic production as a source of the molecule and suggests that salvaging and remodeling by phytoplankton may be less dependent on prokaryotes than previously imagined. We detected -ribazole in the spent media during stationary phase, highlighting eukaryotic production of the molecule as a public good. We provide evidence that -ribazole is produced by this diatom as a mechanism to cope with low cobalamin availability, suggesting that even amongst organisms that dont absolutely require it, cobalamin use has important consequences for fitness. Importance SectionCobalamin (vitamin B12) is a scarce micronutrient in the ocean that impacts the composition and activity of marine microbial communities. Microbes employ a range of strategies to cope with low cobalamin availability, including remodeling cobalamin intermediates and alternatives into cobalamin when the lower ligand is available. Here we show that a recently isolated Thalassiosiraceae diatom doesnt need cobalamin to survive but will take it up and use it when available. Additionally, the diatom produces the lower ligand (-ribazole) under low cobalamin conditions. The production of -ribazole was previously thought to be restricted to bacteria and archaea, so these results suggest that eukaryotes could play a larger role in cobamide remodeling than previously imagined. This work also demonstrates that even organisms that dont absolutely require cobalamin for survival have adopted metabolic strategies to cope with its absence, emphasizing the importance of this vitamin for phytoplankton metabolism.

microbiology↗

bioRxiv2024

Seasonal patterns in b-vitamins and cobalamin co-limitation in the Northwest Atlantic

B-vitamins are important co-enzymes that have long been hypothesized to play key roles in marine ecosystems. However, environmental measurements remain scarce, which limits our understanding of their potential impact. Here, we present mass spectrometry-based measurements of b-vitamins (B1, B2, B3, B5, B6, B12) and related vitamers along a transect in the Northwest Atlantic Ocean, in both particulate phase and dissolved in seawater, seasonally over 5 years, and couple this with targeted investigations of the impact of B12 (cobalamin) on phytoplankton growth. We show that these metabolites are present at femto to pico-molar concentrations and demonstrate that season explains most variance in particulate phase b-vitamins but not dissolved, offering further evidence that metabolite inventories in these two phases are often decoupled. We find correlations between particulate organic carbon with particulate B1 and B3, and between chlorophyll a and particulate B2 and DMB in fall but not spring, indicating unique seasonal drivers of vitamin inventories. Of all measured vitamins, only cobalamin was enriched in the particulate over dissolved phase, predominantly in spring. We documented nitrogen and cobalamin co-limitation of phytoplankton growth during spring bloom decline, when dissolved cobalamin is seemingly drawn down, but not during fall, when dissolved cobalamin concentrations remain elevated. These seasonal differences may be underpinned by the increased importance of cobalamin remodeling and recycling during the fall. This study provides insights into the absolute concentrations, stoichiometry, and variability of b-vitamins in the ocean and offers evidence that cobalamin exerts seasonally-varying controls on Northwest Atlantic marine ecosystems.

microbiology↗

bioRxiv2024

Pseudocobalamin production and use in Synechococcus cultures and communities

Cobalamin influences marine microbial communities because an exogenous source is required by most eukaryotic phytoplankton, and demand can exceed supply. Pseudocobalamin is a cobalamin analog that is produced and used by most cyanobacteria but is not directly available to eukaryotic phytoplankton. Some microbes can remodel pseudocobalamin into cobalamin, but a scarcity of pseudocobalamin measurements impedes our ability to evaluate its importance for marine cobalamin production. Here, we perform simultaneous measurements of pseudocobalamin and methionine synthase (MetH), the key protein that uses it as a co-factor, in Synechococcus cultures and communities. In Synechococcus sp. WH8102, pseudocobalamin quota decreases in low temperature (17 {degrees}C) and low N:P, while MetH did not. Pseudocobalamin and MetH quotas were influenced by culture methods and growth phase. Despite the variability present in cultures, we found a comparably consistent quota of 300 {+/-} 100 pseudocobalamin molecules per cyanobacterial cell in the Northwest Atlantic Ocean, suggesting that cyanobacterial cell counts may be sufficient to estimate pseudocobalamin inventories in this region. This work offers insights into cellular pseudocobalamin metabolism, and the environmental and physiological conditions that may influence it, and provides environmental measurements to further our understanding of when and how pseudocobalamin can influence marine microbial communities.

microbiology↗

bioRxiv2021

Proteomic traits vary across taxa in a coastal Antarctic phytoplankton bloom

Production and use of proteins is under strong selection in microbes, but its unclear how proteome-level traits relate to ecological strategies. We identified and quantified proteomic traits of eukaryotic and prokaryotic microbes through an Antarctic phytoplankton bloom using in situ metaproteomics. To do this, we first used simulations, cultures, and bioinformatic methods to rigorously assess our inferences about various proteomic traits and use these assessments to provide several practical recommendations for researchers using metaproteomics. Different taxa, rather than different environmental conditions, formed distinct clusters based on their ribosomal and photosynthetic proteomic proportions, and we propose that these characteristics relate to ecological differences. We defined and used a proteomic proxy for regulatory cost, which showed that SAR11 had the lowest regulatory cost of any taxa we observed at our summertime Southern Ocean study site. Haptophytes had lower regulatory cost than diatoms, which may underpin haptophyte-to-diatom bloom progression in the Ross Sea. Using metaproteomics, we have quantified several proteomic traits (ribosomal and photosynthetic proteomic proportions, regulatory cost) in eukaryotic and prokaryotic taxa, which can then be incorporated into trait-based models of microbial communities that reflect resource allocation strategies.

microbiology↗

bioRxiv2020

Molecular underpinnings and biogeochemical consequences of enhanced diatom growth in a warming Southern Ocean

The Southern Ocean (SO) harbours some of the most intense phytoplankton blooms on Earth. Changes in temperature and iron availability are expected to alter the intensity of SO phytoplankton blooms, but little is known about how environmental change will influence community composition and downstream biogeochemical processes. We performed experimental manipulations on surface ocean microbial communities from McMurdo Sound in the Ross Sea, with and without iron addition, at −0.5 °C, 3 °C, and 6 °C. We then examined nutrient uptake patterns as well as the growth and molecular responses of two dominant diatoms, Fragilariopsis and Pseudo-nitzschia, to these conditions. We found that nitrate uptake and primary productivity were elevated at increased temperature in the absence of iron addition, and were even greater at high temperature with added iron. Pseudo-nitzschia became more abundant under increased temperature without added iron, while Fragilariopsis required additional iron to benefit from warming. We attribute the apparent advantage Pseudo-nitzschia shows under warming to upregulation of iron-conserving photosynthetic processes, utilization of iron-economic nitrogen assimilation mechanisms, and increased iron uptake and storage. These data identify important molecular and physiological differences between dominant diatom groups and add to the growing body of evidence for Pseudo-nitzschia’s increasingly important role in warming SO ecosystems. This study also suggests that temperature-driven shifts in SO phytoplankton assemblages may increase utilization of the vast pool of excess nutrients in iron-limited SO surface waters, and thereby influence global nutrient distributions and carbon cycle.Significance Statement Phytoplankton assemblages contribute to the Southern Ocean’s ability to absorb atmospheric CO2, form the base of marine food webs, and shape the global distribution of macronutrients. Anthropogenic climate change is altering the SO environment, yet we do not fully understand how resident phytoplankton will react to this change. By comparing the responses of two prominent SO diatom groups to changes in temperature and iron in a natural community, we find that one group, Pseudo-nitzschia, grows better under warmer low-iron conditions by managing cellular iron demand and efficiently increasing photosynthetic capacity. This ability to grow and draw down nutrients in the face of warming, regardless of iron availability, may have major implications for ocean ecosystems and global nutrient and carbon cycles.Competing Interest StatementThe authors have declared no competing interest.View Full Text

ecology↗