Dynamics of transparent exopolymer particle production and aggregation during viral infection of the coccolithophore, Emiliania huxleyi

Abstract

Emiliania huxleyi produces calcium carbonate (CaCO ) coccoliths and transparent exopolymer particles (TEP), sticky, acidic carbohydrates that facilitate aggregation. E. huxleyi's extensive oceanic blooms are often terminated by coccolithoviruses (EhVs) with the transport of cellular debris and associated particulate organic carbon (POC) to depth being facilitated by TEP-bound 'marine snow' aggregates. The dynamics of TEP production and particle aggregation in response to EhV infection are poorly understood. Using flow cytometry, spectrophotometry and FlowCam visualization of alcian blue (AB)-stained aggregates, we assessed TEP production and the size spectrum of aggregates for E. huxleyi possessing different degrees of calcification and cellular CaCO :POC mass ratios, when challenged with two EhVs (EhV207 and EhV99B1). FlowCam imaging also qualitatively assessed the relative amount of AB-stainable TEP (i.e., blue:red ratio of each particle). We show significant increases in TEP during early phase EhV207-infection (∼ 24 h) of calcifying strains and a shift towards large aggregates following EhV99B1-infection. We also observed the formation of large aggregates with low blue:red ratios, suggesting that other exopolymer substances contribute towards aggregation. Our findings show the potential for virus infection and the associated response of their hosts to impact carbon flux dynamics and provide incentive to explore these dynamics in natural populations.

Biochemical diversity of glycosphingolipid biosynthesis as a driver of Coccolithovirus competitive ecology

“…Taken together with field data showing entrainment of fast viruses at depth (Fig. S10), the ‘ differential removal’ model supports enhanced removal of virulent strains from the upper ocean and implicates them in the enhanced production of TEP, particle aggregation and sinking flux (Laber et al ., ; Nissimov et al ., ).…”

“…We argue that it is likely a combination of these two factors that contribute to the competitive success of slow‐infecting EhVs in natural populations. While we acknowledge that multifaceted processes likely drive virus ecology, our empirical lab‐ and field‐based observations here and elsewhere (Vardi et al ., , ; Fulton et al ., ; Hunter et al ., ; Laber et al ., ; Nissimov et al ., ; Sheyn et al ., ) are consistent with SPT functional diversity and GSL production being a driver that helps to explain the competitive ecology of EhV strains infecting E. huxleyi populations in the North Atlantic. There may indeed be other mechanistic drivers that help to shape EhV competitive ecology in the North Atlantic, but they have yet to be demonstrated.…”

“…The rationale for this approach was several fold. First, EhV infection induces the production of sticky transparent exopolymeric particles (TEP), enhancing aggregate formation of infected cells and facilitating downward flux in natural populations in the North Atlantic (Vardi et al ., ; Laber et al ., ; Nissimov et al ., ); this phenomenon is accentuated in fast‐infecting EhV207 and occurs early in infection, absent of lysis (Nissimov et al ., ). Second, we observed an enrichment of EhV207‐like SPT linker amplicons in sinking biomass collected at 150 m at 5 of seven CTD cast stations (Fig.…”

The mutual interplay between calcification and coccolithovirus infection

“…Calcification does indeed appear to play a protective role by serving as a physical barrier from, and adsorption reservoir for, virus particles. The enhanced EhV adsorption characteristics of detached coccoliths combined with their likely entrainment into TEP-derived marine particles and aggregates (Laber et al, 2018;Nissimov et al, 2018;Sheyn et al, 2018) suggest that this might be an effective strategy to remove EhVs and function as an effective loss term. In this way, differential calcification states (coccolith morphologies and calcite content), arising from different genetic makeups, morphotype biogeographical patterns and nutrient availabilities, may critically structure epicentres of EhV infection in the ocean.…”

“…Globally distributed blooms of E. huxleyi, which spañ 100,000 km 2 (Brown and Yoder, 1994;Brown, 1995;Tyrell and Merico, 2004), are often terminated by infection of lytic, double-stranded DNA containing coccolithoviruses (EhVs) (Bratbak et al, 1993;Schroeder et al, 2003;Vardi et al, 2012). Infection triggers cell lysis and the release of dissolved organic carbon (DOC) and PIC-laden coccoliths in surface waters along with the production of transparent expolymeric particles (TEP; Passow et al, 2001;Passow, 2002;Lehahn et al, 2014), which facilitate particle aggregation, high zooplankton grazing and greater downward vertical fluxes of both POC and PIC from the upper mixed layer (Laber et al, 2018;Sheyn et al, 2018;Nissimov et al, 2018). Emiliania huxleyi-EhV interactions are mechanistically regulated by a lipid-based, chemical arms race, with three structurally distinct membrane glycosphingolipids (GSLs)host GSLs (hGSLs), virus GSLs (vGSLs) and sialic acid GSLs (sGSLs)at the core of this interaction, each serving a unique diagnostic indicator of different aspects of the infection process Bidle, 2015).…”