Reduction in photosystem II efficiency during a virus-controlled Emiliania huxleyi bloom

Abstract

During viral infection of Emiliania huxleyi, laboratory studies have shown that photosystem (PS) II efficiency declines during the days post-infection and is thought to be associated with viral-induced interruption of electron transport rates between photosystems. However, measuring the impact of viral infection on PSII function in E. huxleyi populations from natural, taxo nomically diverse phytoplankton communities is difficult, and whether this phenomenon occurs in nature is presently unknown. Here, chlorophyll fluorescence analysis was used to assess changes in PSII efficiency throughout an E. huxleyi bloom during a mesocosm experiment off the coast of Norway. Specifically, we aimed to determine whether a measurable suppression of the efficiency of PSII photochemistry could be observed due to viral infection of the natural E. huxleyi populations. During the major infection period prior to bloom collapse, there was a significant reduction in PSII efficiency with an average decrease in maximum PSII photochemical efficiency (F v /F m ) of 17% and a corresponding 75% increase in maximum PSII effective absorption crosssection (σ PSII ); this was concurrent with a significant decrease in E. huxleyi growth rates and an increase in E. huxleyi virus (EhV) production. As E. huxleyi populations dominated the phytoplankton community and potentially contributed up to 100% of the chlorophyll a pool, we believe that the variable chlorophyll fluorescence signal measured during this period was derived predominantly from E. huxleyi and, thus, reflects changes occurring within E. huxleyi cells. This is the first demonstration of suppression of PSII photochemistry occurring during viral infection of natural coccolithophore populations. KEY WORDS: Viral infection · Emiliania huxleyi bloom · Chlorophyll fluorescence · Photosystem II efficiency · MesocosmResale or republication not permitted without written consent of the publisher Editorial responsibility: Katherine Richardson,

Modulation of host ROS metabolism is essential for viral infection of a bloom-forming coccolithophore in the ocean

“…ROS was previously proposed to be associated with viral infection and specifically with induction of hallmarks of programmed cell death during the lytic phase of infection in E. huxleyi cultures (Evans et al, 2006) and mesocosm experiments (Vardi et al, 2012). Recent reports have shown a reduction in the photosystem II efficiency, chlorophyll degradation and carotenoid production during E. huxleyi infection, supporting a possible source for ROS generation (Evans et al, 2006;Bidle et al, 2007;Llewellyn et al, 2007;Bale et al, 2013;Kimmance et al, 2014). Our transcriptome analysis suggested an additional enzymatic source for ROS production by induction of NADPH oxidase (Figure 1).…”

The mutual interplay between calcification and coccolithovirus infection

“…Culture growth and maintenance Emiliania huxleyi strains DHB607, DHB611, DHB624 and DHB659 were obtained from the Plymouth Culture Collection of Marine Microalgae (http://www.mba.ac.uk/ culture-collection/). These strains had been previously isolated via flow cytometry and single cell sorting by D. J. Hinz et al (personal communication) during a 2008 mesocosm experiment conducted in Blomsterdalen, Norway (Vardi et al, 2012;Kimmance et al, 2014). CCMP374 and CCMP1516 were obtained from the National Center for Marine Algae and Micobiota (https:// ncma.bigelow.org).…”

Intragenus competition between coccolithoviruses: an insight on how a select few can come to dominate many

“…The demise of coccolithophore blooms in temperate and sub‐temperate oceans has been predominantly attributed to the impact of viral infection (Bratbak et al ., ; Martínez‐Martínez et al ., ; Brussaard et al ., ; Sorensen et al ., ). Their role in regulating coccolithophore populations has been firmly established via studies of natural environmental systems (Wilson et al ., ; Schroeder et al ., ; Martínez‐Martínez et al ., ; Vardi et al ., ) and induced semi‐natural blooms in the Norwegian fjords (Bratbak et al ., ; Jacquet et al ., ; Pagarete et al ., ; Kimmance et al ., ). In addition to the direct reduction in total cell abundance, the species‐specific nature of viruses leads to the regulation of interspecies competition and succession within a mixed phytoplankton community (Fuhrman, ; Brussaard, ).…”