Larsen Aud

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Larsen
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Aud
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  • Article
    Virus infection of Haptolina ericina and Phaeocystis pouchetii implicates evolutionary conservation of programmed cell death induction in marine haptophyte–virus interactions
    (Oxford University Press, 2014-05-05) Ray, Jessica L. ; Haramaty, Liti ; Thyrhaug, Runar ; Fredricks, Helen F. ; Van Mooy, Benjamin A. S. ; Larsen, Aud ; Bidle, Kay D. ; Sandaa, Ruth-Anne
    The mechanisms by which phytoplankton cope with stressors in the marine environment are neither fully characterized nor understood. As viruses are the most abundant entities in the global ocean and represent a strong top-down regulator of phytoplankton abundance and diversity, we sought to characterize the cellular response of two marine haptophytes to virus infection in order to gain more knowledge about the nature and diversity of microalgal responses to this chronic biotic stressor. We infected laboratory cultures of the haptophytes Haptolina ericina and Phaeocystis pouchetii with CeV-01B or PpV-01B dsDNA viruses, respectively, and assessed the extent to which host cellular responses resemble programmed cell death (PCD) through the activation of diagnostic molecular and biochemical markers. Pronounced DNA fragmentation and activation of cysteine aspartate-specific proteases (caspases) were only detected in virus-infected cultures of these phytoplankton. Inhibition of host caspase activity by addition of the pan-caspase inhibitor z-VAD-fmk did not impair virus production in either host–virus system, differentiating it from the Emiliania huxleyi-Coccolithovirus model of haptophyte–virus interactions. Nonetheless, our findings point to a general conservation of PCD-like activation during virus infection in ecologically diverse haptophytes, with the subtle heterogeneity of cell death biochemical responses possibly exerting differential regulation on phytoplankton abundance and diversity.
  • Article
    The possession of coccoliths fails to deter microzooplankton grazers
    (Frontiers Media, 2020-12-02) Mayers, Kyle M. J. ; Poulton, Alex J. ; Bidle, Kay D. ; Thamatrakoln, Kimberlee ; Schieler, Brittany ; Giering, Sarah L. C. ; Wells, Seona R. ; Tarran, Glen A. ; Mayor, Daniel J. ; Johnson, Matthew D. ; Riebesell, Ulf ; Larsen, Aud ; Vardi, Assaf ; Harvey, Elizabeth L.
    Phytoplankton play a central role in the regulation of global carbon and nutrient cycles, forming the basis of the marine food webs. A group of biogeochemically important phytoplankton, the coccolithophores, produce calcium carbonate scales that have been hypothesized to deter or reduce grazing by microzooplankton. Here, a meta-analysis of mesocosm-based experiments demonstrates that calcification of the cosmopolitan coccolithophore, Emiliania huxleyi, fails to deter microzooplankton grazing. The median grazing to growth ratio for E. huxleyi (0.56 ± 0.40) was not significantly different among non-calcified nano- or picoeukaryotes (0.71 ± 0.31 and 0.55 ± 0.34, respectively). Additionally, the environmental concentration of E. huxleyi did not drive preferential grazing of non-calcified groups. These results strongly suggest that the possession of coccoliths does not provide E. huxleyi effective protection from microzooplankton grazing. Such indiscriminate consumption has implications for the dissolution and fate of CaCO3 in the ocean, and the evolution of coccoliths.