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Arctic marine microbial eukaryotes in the face of climate change
Examining the physiological responses of marine microbial phytoplankton species to oceanic change.
Focus 1: Understanding the dynamics of phytoplankton and other microbial species assemblage in the face of oceanic change
A Decadal Perspective on North Water Microbial Eukaryotes as Arctic Ocean Sentinels.
Freyria et al., 2021, Sci. Rep.
Main goal: In an effort to disentangle season versus interannual and spatial differences, we investigated the variability of marine microbial eukaryotes from two sides of the North Water region.
Results: Community composition was tied to seasonality with summer communities more variable than distinct October communities. In summer, sentinel pan-Arctic species, including a diatom in the Chaetoceros socialis-gelidus complex and the picochlorophyte Micromonas polaris dominated phytoplankton and were summer specialists. In autumn, uncultured undescribed open water dinoflagellates were favored, and their ubiquity suggests they are sentinels of arctic autumn conditions. Overall, the summer sentinel microbial taxa are persisting, and a subset oceanic dinoflagellate should be monitored for possible ecosystem shifts as later autumn ice formation becomes prevalent elsewhere.
Shotgun metagenomics reveils the flexibility and diversity of Arctic marine microbiomes.
Freyria et al., 2024, ISME Comm.
Main goal: Climate warming is already occurring in polar regions, where physical oceanography and ice melt influence microbial species composition and activity. We hypothesized that microbial community taxonomic and functional signatures are closely linked to the in-situ environment within the latitudinal constraints of polar regions.
Results: Our findings provide increased understanding of the function of microbes in the ecosystem and their potential interactions within the polar environment. The results of our study demonstrate that the microbial community in the North Water pelagic zone has the genetic capacity for potential bio-attenuation of methane, as well as metabolising hydrocarbon compounds into key intermediates of carbon metabolism.
Focus 2: Assessing the genetic capacity of Arctic microalgae to tolerate salinity fluctuations
Salinity Tolerance Mechanisms of an Arctic Pelagophyte Using Comparative Transcriptomic and Gene Expression Analysis.
Freyria et al., 2022, Comm. Biol.
Main goal: The aim of this study was to determine the range and response of CCMP2097 to changes in salinity, to gain a deeper understanding of the potential genetic capacity of an ice-associated Arctic alga to adjust to a range of realistic salinities that would be encountered in its ice influenced habitat.
Results: We show overexpression of Na+–H+ antiporters and Na+–Pi symporters as salinity decreases, but with K+-channel complex overexpressed at higher salinities. More surprisingly, we found the potential implications of ice-binding proteins and antifreeze proteins with differential expression under the tested salinity conditions, suggesting tight coupling between cold temperature adaptation and salinity. We speculate that these key genes confer properties to adapt to progressive changes in salinity and facilitate survival in the sea-ice-influenced ocean.
Stress Responses in an Arctic Microalga (Pelagophyceae) Following Sudden Salinity Change Revealed by Gene Expression Analysis
Freyria et al., 2024, Comm. Biol.
Main goal: To investigate algal responses to lowered salinity, we analysed the responses and acclimatation over 24h in a non-model Arctic marine alga (pelagophyte CCMP2097) following transfer to realistic lower salinities.
Results: Using RNA-seq transcriptomics, here we show rapid differentially expressed genes related to stress oxidative responses, proteins involved in the photosystem and circadian clock, and those affecting lipids and inorganic ions. After 24h the pelagophyte adjusted to the lower salinity seen in the overexpression of genes associated with freezing resistance, cold adaptation, and salt tolerance. Overall, a suite of ancient widespread pathways is recruited enabling the species to adjust to the stress of rapid salinity change.
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