The Calcium Carbonate Shell of Emiliania huxleyi Provides Limited Protection Against Viral Infection

Abstract

Coccolithophores are an important group of marine phytoplankton which cover themselves with the coccosphere -a shell composed of numerous calcium carbonate (CaCO 3 ) platelets. Despite more than a century of coccolithophore research, it remains speculative why coccolithophores calcify. Resolving this question is essential to assess the competitive fitness of coccolithophores in the future ocean where changes in calcification are expected. Here, we used the Emiliania huxleyi -Emiliania huxleyi Virus 86 host-virus model system to test the hypothesis that the coccosphere serves as a physical barrier reducing viral infection. Therefore, we removed the coccosphere from living E. huxleyi cells and compared the infection progress relative to calcified cells in a series of 6 experiments under different growth conditions. We found that the coccosphere does not constitute an effective physical barrier against viral penetration, since non-growing calcified cells were susceptible to viral infection and lysis (growth stopped by light limitation). However, we also found that protection against the virus may depend on the daily growth cycle. E. huxleyi reached higher peak abundances when decalcified cells were allowed to rebuild their coccosphere before entering cell division phase and being exposed to the virus, thereby suggesting that rates of viral infection could be reduced by the coccosphere during the critical phase in the cell cycle. However, the benefit of this potential protection is arguably of limited ecological significance since the concentrations of both, calcified and decalcified E. huxleyi approached similar values until the end of the bloom. We conclude that the coccosphere provides at best a limited protection against infection with the EhV86.

Raman Microspectroscopy Goes Viral: Infection Dynamics in the Cosmopolitan Microalga, Emiliania huxleyi

“…It is worth noting that while we used a commonly studied non-calcified E. huxleyi strain (e.g., Bidle et al, 2007 ; Evans et al, 2007 ; Johns et al, 2019 ; Gilg et al, 2016 ; Pasulka et al, 2018 ; Goode et al, 2019 ; Knowles et al, 2020 ), we expect the results from this study are also representative of infection of calcified strains. The infection dynamics and virion production are not significantly impacted by whether the host cells are calcified or not ( Paasche, 2001 ; Haunost et al, 2020 ). However, variations in strains of hosts and virions and host physiology more likely account for reported differences in infection success and dynamics ( Allen et al, 2007 ; Kegel et al, 2013 ).…”

Abundances and morphotypes of the coccolithophore <i>Emiliania huxleyi</i> in southern Patagonia compared to neighbouring oceans and Northern Hemisphere fjords

“…The lightly calcified A morphotype was rare and did not show any clear pattern in its distribution. The A-CC morphotype has been associated with coastal upwelling zones in the Atlantic (Giraudeau et al, 1993;Smith et al, 2012;Henderiks et al, 2012) but not reported from the 7-18 33.4-35.6 Poulton et al (20117-18 33.4-35.6 Poulton et al ( , 2013 a E. huxleyi as a component of larger coccolithophore assemblages. When information about other coccolithophores was provided, the percentage abundance of E. huxleyi is given or if it was noted that E. huxleyi was dominant.…”

Cell-Penetrating Peptide Delivery of Nucleic Acid Cargo to Emiliania huxleyi, a Calcifying Marine Coccolithophore

“…Cells were decalcified prior to experiments using an established low-pH decalcification protocol. 25 A Beckman Coulter Z2 with a 100 μm orifice was used to collect cell count and median cell size as described by Fan et al 22 Decalcified cells were measured in bulk at 0 h, then aliquoted into a well plate prior to treating with 10 μΜ CPP-PNA. Throughout the incubation process, the cells were maintain in standard L1-Si/25 media.…”