Biology subjects

Lovejoy, C.

Publications and source records attributed to Lovejoy, C..

8 recordsLinked to original sources

bioRxiv2024

Temporal dynamics and biogeography of sympagic and planktonic autotrophic microbial eukaryotes during the under-ice Arctic bloom

Photosynthetic microbial eukaryotes play a pivotal role as primary producers in the Arctic Ocean, where seasonal blooms within and below the ice are crucial phenomena, contributing significantly to global primary production and biogeochemical cycling. In this study, we investigated the taxonomic composition of sympagic algae and phytoplankton communities during the Arctic under-ice spring bloom using metabarcoding of the 18S rRNA gene. Samples were obtained from three size fractions over a period of nearly three months at an ice camp deployed on landfast ice off the coast of Baffin Island as part of the Green Edge project. We classified the major sympagic and phytoplankton taxa found in this study into biogeographical categories using publicly available metabarcoding data from more than 2 800 oceanic and coastal marine samples. This study demonstrated the temporal succession of taxonomic groups during the development of the under-ice bloom, illustrated by an overall transition from polar to polar-temperate taxa, in particular in the smallest size fraction. Overlooked classes such as Pelagophyceae (undescribed Pelagomonadales clade A1 and the genus Ankylochrysis), Bolidophyceae (Parmales environmental clade 2), and Cryptophyceae (Baffinella frigidus) might play a greater role than anticipated within the pico-sized communities in and under the ice pack during the pre-bloom period. Finally, we emphasize the importance of microdiversity, taking the example of B. frigidus for which a new strain isolated during Green Edge represents an ice ecotype while the type strain is clearly linked to marine waters.

ecology↗

bioRxiv2022

Scaled-expansion of the membrane associated cytoskeleton requires conserved kinesin adaptors

A periodic lattice of actin rings and spectrin tetramers scaffolds the axonal membrane. How spectrin is delivered to this structure to scale its size to that of the growing axon is unknown. We found that endogenous spectrin, visualized with singe axon resolution in vivo, is delivered to hotspots in the lattice that support its expansion at rates set by axon stretch-growth. Unlike other cytoskeletal proteins, whose apparent slow movement consists of intermittent bouts of fast movements, spectrin moves slowly and processively. We identified a pair of coiled coil proteins that mediate this slow movement and the expansion of the lattice by linking spectrin to kinesin-1. Thus, processive slow transport and local lattice incorporation support scaled cytoskeletal expansion during axon stretch-growth. One-Sentence SummaryKinesin adaptors control spectrin transport and expansion of the membrane periodic skeleton.

cell biology↗

bioRxiv2022

Arctic phytoplankton spring bloom diversity across the marginal ice zone in Baffin Bay

Phytoplankton under-ice blooms have been recently recognized as an important Arctic phenomenon for global primary production and biogeochemical cycling. Drastic sea-ice decline in both extension and thickness enables the development of early blooms, sometimes hundreds of kilometers beneath the pack ice. Baffin Bay is a semi-enclosed sea where Arctic and North Atlantic water masses interact. It is totally covered by sea-ice by March and ice-free by August/September. In the present work, we investigated the phytoplankton community structure across the marginal ice zone between the ice-free, Atlantic-influenced, east and the ice-covered, Arctic-influenced, west Baffin Bay using 18S rRNA high-throughput amplicon sequencing, flow cytometry cell counting and numerous environmental and biological data collected and compiled in the scope of the Green Edge project. Sampling was performed during June-July 2016 in a total of 16 stations with around 6 depths each. Stations were clustered into "Under Ice" (UI), "Marginal Ice Zone" (MIZ) and "Open Water" (OW) on the basis of its sea ice cover upon sampling. Phytoplankton community structure was analyzed by 18S rRNA metabarcoding with the microdiversity approach. The UI sector was characterized by a shallow nitracline, high pico-phytoplankton abundance and a shared dominance between Micromonas and Phaeocystis in the 0.2-3 {micro}m size fraction, as well as an increased contribution of Cryptophyceae and non-diatom Ochrophyta in the 3-20 {micro}m size fraction. Several amplicon sequence variants (ASVs) were flagged as indicator for the UI+MIZ sector group, including known ice-associated taxa such as the diatoms Melosira arctica and Pseudo-nitzschia seriata, but also specific ASVs assigned to the green alga Micromonas polaris and the cryptophyte Falcomonas daucoides, the silicoflagellate Dictyocha speculum, one member of the uncultivated MOCH-2 group, and a Pterosperma sp. (green algae) rarely seen in other metabarcoding datasets, including from the Arctic. The OW sector harbored a community adapted to a nutrient-depleted/high light environment, with a significant contribution of the haptophytePhaeocystis pouchetii and big centric diatoms, including several Thalassiosira species.

microbiology↗

bioRxiv2021

Within-Arctic horizontal gene transfer as a driver of convergent evolution in distantly related microalgae

The Arctic Ocean is being impacted by warming temperatures, increasing freshwater and highly variable ice conditions. The microalgal communities underpinning Arctic marine food webs, once thought to be dominated by diatoms, include a phylogenetically diverse range of small algal species, whose biology remains poorly understood. Here, we present genome sequences of a cryptomonad, a haptophyte, a chrysophyte, and a pelagophyte, isolated from the Arctic water column and ice. Comparing protein family distributions and sequence similarity across a densely-sampled set of algal genomes and transcriptomes, we note striking convergences in the biology of distantly related small Arctic algae, compared to non-Arctic relatives; although this convergence is largely exclusive of Arctic diatoms. Using high-throughput phylogenetic approaches, incorporating environmental sequence data from Tara Oceans, we demonstrate that this convergence was partly explained by horizontal gene transfers (HGT) between Arctic species, in over at least 30 other discrete gene families, and most notably in ice-binding domains (IBD). These Arctic-specific genes have been repeatedly transferred between Arctic algae, and are independent of equivalent HGTs in the Antarctic Southern Ocean. Our data provide insights into the specialized Arctic marine microbiome, and underlines the role of geographically-limited HGT as a driver of environmental adaptation in eukaryotic algae.

evolutionary biology↗

bioRxiv2020

Environmental vulnerability of the global ocean plankton community interactome

Marine plankton form complex communities of interacting organisms at the base of the food web, which sustain oceanic biogeochemical cycles, and help regulate climate. Though global surveys are starting to reveal ecological drivers underlying planktonic community structure, and predicted climate change responses, it is unclear how community-scale species interactions will be affected by climate change. Here we leveraged Tara Oceans sampling to infer a global ocean cross-domain plankton co-occurrence network - the community interactome - and used niche modeling to assess its vulnerabilities to environmental change. Globally, this revealed a plankton interactome self-organized latitudinally into marine biomes (Trades, Westerlies, Polar), and more connected poleward. Integrated niche modeling revealed biome-specific community interactome responses to environmental change, and forecasted most affected lineages for each community. These results provide baseline approaches to assess community structure and organismal interactions under climate scenarios, while identifying plausible plankton bioindicators for ocean monitoring of climate change.

ecology↗

bioRxiv2020

Histone Acetyltransferase 1 is Required for DNA Replication Fork Function and Stability

The replisome functions in a dynamic environment that is at the intersection of parental and nascent chromatin. Parental nucleosomes are disrupted in front of the replication fork. The daughter duplexes are packaged with an equal amount of parental and newly synthesized histones in the wake of the replication fork through the action of the replication-coupled chromatin assembly pathway. Histone acetyltransferase 1 (Hat1) is responsible for the cytosolic diacetylation of newly synthesized histone H4 on lysines 5 and 12 that accompanies replication-coupled chromatin assembly. Analysis of the role of Hat1 in replication-coupled chromatin assembly demonstrates that Hat1 also physically associates with chromatin near sites of DNA replication. The association of Hat1 with newly replicated DNA is transient but can be stabilized by replication fork stalling. The association of Hat1 with nascent chromatin may be functionally relevant as loss of Hat1 results in a decrease in replication fork progression and an increase in replication fork stalling. In addition, in the absence of Hat1, stalled replication forks are unstable and newly synthesized DNA becomes susceptible to Mre11-dependent degradation. These results suggest that Hat1 links replication fork function to the proper processing and assembly of newly synthesized histones.

biochemistry↗

bioRxiv2019

Diversity, biogeography, and evidence for endemism of SAR11 bacteria from the Arctic Ocean

The Arctic Ocean is relatively isolated from other oceans and consists of strongly stratified water masses with distinct histories, nutrient, temperature and salinity characteristics, therefore providing an optimal environment to investigate local adaptation. The globally distributed SAR11 bacterial group consists of multiple ecotypes that are associated with particular marine environments, yet relatively little is known about Arctic SAR11 diversity. Here, we examined SAR11 diversity using ITS analysis and metagenome-assembled genomes (MAGs). Arctic SAR11 assemblages were comprised of the S1a, S1b, S2, and S3 clades, and structured by water mass and depth. The fresher surface layer was dominated by an ecotype (S3-derived P3.2) previously associated with Arctic and brackish water. In contrast, deeper waters of Pacific origin were dominated by the P2.3 ecotype of the S2 clade, within which we identified a novel subdivision (P2.3s1) that was rare outside the Arctic Ocean. Arctic S2-derived SAR11 MAGs were restricted to high latitudes and included MAGs related to the recently defined S2b subclade, a finding consistent with bi-polar ecotypes and Arctic endemism. These results place the stratified Arctic Ocean into the SAR11 global biogeography and have identified SAR11 lineages for future investigation of adaptive evolution in the Arctic Ocean.

microbiology↗

bioRxiv2018

Genomic evidence for the degradation of terrestrial organic matter by pelagic Arctic Ocean Chloroflexi bacteria

The Arctic Ocean currently receives a large supply of global river discharge and terrestrial dissolved organic matter. Moreover, an increase in freshwater runoff and riverine transport of organic matter to the Arctic Ocean is a predicted consequence of thawing permafrost and increased precipitation. The fate of the terrestrial humic-rich organic material and its impact on the marine carbon cycle are largely unknown. Here, the first metagenomic survey of the Canada Basin in the Western Arctic Ocean showed that pelagic Chloroflexi from the Arctic Ocean are replete with aromatic compound degradation genes, acquired in part by lateral transfer from terrestrial bacteria. Our results imply marine Chloroflexi have the capacity to use terrestrial organic matter and that their role in the carbon cycle may increase with the changing hydrological cycle.

microbiology↗