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Coccolithophores are an important group of calcifying marine phytoplankton. Although coccolithophores are not silicified, some species exhibit a requirement for Si in the calcification process. These species also possess a novel protein (SITL) that resembles the SIT family of Si transporters found in diatoms. However, the nature of Si transport in coccolithophores is not yet known, making it difficult to determine the wider role of Si in coccolithophore biology. Here, we show that coccolithophore SITLs act as Na+‐coupled Si transporters when expressed in heterologous systems and exhibit similar characteristics to diatom SITs. We find that CbSITL from Coccolithus braarudii is transcriptionally regulated by Si availability and is expressed in environmental coccolithophore populations. However, the Si requirement of C. braarudii and other coccolithophores is very low, with transport rates of exogenous Si below the level of detection in sensitive assays of Si transport. As coccoliths contain only low levels of Si, we propose that Si acts to support the calcification process, rather than forming a structural component of the coccolith itself. Si is therefore acting as a micronutrient in coccolithophores and natural populations are only likely to experience Si limitation in circumstances where dissolved silicon (DSi) is depleted to extreme levels. [ABSTRACT FROM AUTHOR]

Summary: The development of calcification by the coccolithophores had a profound impact on ocean carbon cycling, but the evolutionary steps leading to the formation of these complex biomineralized structures are not clear. Heterococcoliths consisting of intricately shaped calcite crystals are formed intracellularly by the diploid life cycle phase. Holococcoliths consisting of simple rhombic crystals can be produced by the haploid life cycle stage but are thought to be formed extracellularly, representing an independent evolutionary origin of calcification.We use advanced microscopy techniques to determine the nature of coccolith formation and complex crystal formation in coccolithophore life cycle stages.We find that holococcoliths are formed in intracellular compartments in a similar manner to heterococcoliths. However, we show that silicon is not required for holococcolith formation and that the requirement for silicon in certain coccolithophore species relates specifically to the process of crystal morphogenesis in heterococcoliths.We therefore propose an evolutionary scheme in which the lower complexity holococcoliths represent an ancestral form of calcification in coccolithophores. The subsequent recruitment of a silicon‐dependent mechanism for crystal morphogenesis in the diploid life cycle stage led to the emergence of the intricately shaped heterococcoliths, enabling the formation of the elaborate coccospheres that underpin the ecological success of coccolithophores. See also the Commentary on this article by Mock, 231: 1663–1666. [ABSTRACT FROM AUTHOR]

Microplastics are of increasing concern as they are readily ingested by aquatic organisms. This study investigated microplastic trophic transfer using larval inland silversides (Menidia beryllina) (5 d posthatch) and unicellular tintinnid (Favella spp.) as a model food chain relevant to North American estuaries. Low‐density polyethylene microspheres (10–20 μm) were used to compare direct ingestion of microplastics by larval fish and trophic transfer via tintinnid prey. Dichlorodiphenyltrichloroethane (DDT)‐treated microspheres were used to determine sorbed pollutant effects on microplastic ingestion. Larval fish exposed directly to microspheres ingested significantly fewer than those exposed via contaminated prey. Larvae ingested significantly more ciliates containing DDT‐treated microspheres than ciliates containing untreated plastics but did not discriminate when exposed directly. Larvae reared for 16 d following a direct 2 h exposure had significantly lower wet weight values than unexposed controls. Our results demonstrate that trophic transfer is a significant route of microplastic exposure that can cause detrimental effects in sensitive life stages. [ABSTRACT FROM AUTHOR]

Commercial fisheries yield essential foods, sustain cultural practices, and provide widespread employment around the globe. Commercially harvested species face a myriad of anthropogenic threats including degraded habitats, changing climate, overharvest, and pollution. Microplastics are pollutants of increasing concern, which are pervasive in the environment and can harbor or adsorb pollutants from surrounding waters. Aquatic organisms, including commercial species, encounter and ingest microplastics, but there is a paucity of data about those caught and cultured in North America. Additional research is needed to determine prevalence, physiological effects, and population‐level implications of microplastics in commercial species from Canada, the United States, and Mexico. Investigations into possible human health effects of microplastic exposure from seafood are also greatly needed. This synthesis summarizes current knowledge, identifies data gaps, and provides future research directions for addressing microplastics effects in commercially valuable North American fishery species. [ABSTRACT FROM AUTHOR]

Brevetoxin (PbTx) is a neurotoxic secondary metabolite of the dinoflagellate Karenia brevis. We used a novel, fluorescent BODIPY‐labeled conjugate of brevetoxin congener PbTx‐2 (B‐PbTx) to track absorption of the metabolite into a variety of marine microbes. The labeled toxin was taken up and brightly fluoresced in lipid‐rich regions of several marine microbes including diatoms and coccolithophores. The microzooplankton (20–200 μm) tintinnid ciliate Favella sp. and the rotifer Brachionus rotundiformis also took up B‐PbTx. Uptake and intracellular fluorescence of B‐PbTx was weak or undetectable in phytoplankton species representative of dinoflagellates, cryptophytes, and cyanobacteria over the same (4 h) time course. The cellular fate of two additional BODIPY‐conjugated K. brevis associated secondary metabolites, brevenal (B‐Bn) and brevisin (B‐Bs), were examined in all the species tested. All taxa exhibited minimal or undetectable fluorescence when exposed to the former conjugate, while most brightly fluoresced when treated with the latter. This is the first study to observe the uptake of fluorescently‐tagged brevetoxin conjugates in non‐toxic phytoplankton and zooplankton taxa, demonstrating their potential in investigating whether marine microbes can serve as a significant biological sink for algal toxins. The highly variable uptake of B‐PbTx observed among taxa suggests some may play a more significant role than others in vectoring lipophilic toxins in the marine environment. [ABSTRACT FROM AUTHOR]

Summary: Coccolithophores are globally distributed unicellular marine algae that are characterized by their covering of calcite coccoliths. Calcification by coccolithophores contributes significantly to global biogeochemical cycles. However, the physiological requirement for calcification remains poorly understood as non‐calcifying strains of some commonly used model species, such as Emiliania huxleyi, grow normally in laboratory culture. To determine whether the requirement for calcification differs between coccolithophore species, we utilized multiple independent methodologies to disrupt calcification in two important species of coccolithophore: E. huxleyi and Coccolithus braarudii. We investigated their physiological response and used time‐lapse imaging to visualize the processes of calcification and cell division in individual cells. Disruption of calcification resulted in major growth defects in C. braarudii, but not in E. huxleyi. We found no evidence that calcification supports photosynthesis in C. braarudii, but showed that an inability to maintain an intact coccosphere results in cell cycle arrest. We found that C. braarudii is very different from E. huxleyi as it exhibits an obligate requirement for calcification. The identification of a growth defect in C. braarudii resulting from disruption of the coccosphere may be important in considering their response to future changes in ocean carbonate chemistry. [ABSTRACT FROM AUTHOR]

Background. The potent neurotoxins produced by the harmful algal bloom species Karenia brevis are activators of sodium voltage-gated channels (VGC) in animals, re- sulting in altered channel kinetics and membrane hyperexcitability. Recent biophysical and genomic evidence supports widespread presence of homologous sodium (Na+) and calcium (Ca2+) permeable VGCs in unicellular algae, including marine phytoplankton. We therefore hypothesized that VGCs of these phytoplankton may be an allelopathic target for waterborne neurotoxins produced by K. brevis blooms that could lead to ion channel dysfunction and disruption of signaling in a similar manner to animal Na+ VGCs. Methods. We examined the interaction of brevetoxin-3 (PbTx-3), a K. brevis neu- rotoxin, with the Na+/Ca2+ VGC of the non-toxic diatom Odontella sinensis using electrophysiology. Single electrode current- and voltage- clamp recordings from O. sinensis in the presence of PbTx-3 were used to examine the toxin's effect on voltage gated Na+/Ca2+ currents. In silico analysis was used to identify the putative PbTx binding site in the diatoms. We identified Na+/Ca2+ VCG homologs from the transcriptomes and genomes of 12 diatoms, including three transcripts from O. sinensis and aligned them with site-5 of Na+ VGCs, previously identified as the PbTx binding site in animals. Results. Up to 1 mM PbTx had no effect on diatom resting membrane potential or membrane excitability. The kinetics of fast inward Na+/Ca2+ currents that underlie diatom action potentials were also unaffected. However, the peak inward current was inhibited by 33%, delayed outward current was inhibited by 25%, and reversal potential of the currents shifted positive, indicating a change in permeability of the underlying channels. Sequence analysis showed a lack of conservation of the PbTx binding site in diatom VGC homologs, many of which share molecular features more similar to single-domain bacterial Na+/Ca2+ VGCs than the 4-domain eukaryote channels. Discussion. Although membrane excitability and the kinetics of action potential currents were unaffected, the permeation of the channels underlying the diatom action potential was significantly altered in the presence of PbTx-3. However, at environmentally relevant concentrations the effects of PbTx- on diatom voltage activated currents and interference of cell signaling through this pathway may be limited. The relative insensitivity of phytoplankton VGCs may be due to divergence of site-5 (the putative PbTx binding site), and in some cases, such as O. sinensis, resistance to toxin effects may be because of evolutionary loss of the 4-domain eukaryote channel, while retaining a single domain bacterial-like VGC that can substitute in the generation of fast action potentials. [ABSTRACT FROM AUTHOR]

Alveolate (ciliates and dinoflagellates) grazers are integral components of the marine food web and must therefore be able to sense a range of mechanical and chemical signals produced by prey and predators, integrating them via signal transduction mechanisms to respond with effective prey capture and predator evasion behaviors. However, the sensory biology of alveolate grazers is poorly understood. Using novel techniques that combine electrophysiological measurements and high-speed videomicroscopy, we investigated the sensory biology of Favella sp., a model alveolate grazer, in the context of its trophic ecology. Favella sp. produced frequent rhythmic depolarizations (~500 ms long) that caused backward swimming and are responsible for endogenous swimming patterns relevant to foraging. Contact of both prey cells and non-prey polystyrene microspheres at the cilia produced immediate mechanostimulated depolarizations (~500 ms long) that caused backward swimming, and likely underlie aggregative swimming patterns of Favella sp. in response to patches of prey. Contact of particles at the peristomal cavity that were not suitable for ingestion resulted in depolarizations after a lag of ~600 ms, allowing time for particles to be processed before rejection. Ingestion of preferred prey particles was accompanied by transient hyperpolarizations (~1 s) that likely regulate this step of the feeding process. Predation attempts by the copepod Acartia tonsa elicited fast (~20 ms) animal-like action potentials accompanied by rapid contraction of the cell to avoid predation. We have shown that the sensory mechanisms of Favella sp. are finely tuned to the type, location, and intensity of stimuli from prey and predators. [ABSTRACT FROM AUTHOR]

Coccolithophores are the most significant producers of marine biogenic calcite, although the intracellular calcification process is poorly understood. In the case of Scyphosphaera apsteinii Lohmann 1902, flat ovoid muroliths and bulky, vase-shaped lopadoliths with a range of intermediate morphologies may be produced by a single cell. This polymorphic species is within the Zygodiscales, a group that remains understudied with respect to ultrastructure and coccolith ontogeny. We therefore undertook an analysis of cell ultrastructure, morphology, and coccolithogenesis. The cell ultrastructure showed many typical haptophyte features, with calcification following a similar pattern to that described for other heterococcolith bearing species including Emiliania huxleyi. Of particular significance was the reticular body role in governing fine-scale morphology, specifically the central pore formation of the coccolith. Our observations also highlighted the essential role of the inter- and intracrystalline organic matrix in growth and arrangement of the coccolith calcite. S. apsteinii secreted mature coccoliths that attached to the plasma membrane via fibrillar material. Time-lapse light microscopy demonstrated secretion of lopadoliths occurred base first before being actively repositioned at the cell surface. Significantly, growth irradiance influenced the coccosphere composition with fewer lopadoliths being formed relative to muroliths at higher light intensities. Overall, our observations support dynamic metabolic (i.e., in response to growth irradiance), sensory and cytoskeletal control over the morphology and secretion of polymorphic heterococcoliths. With a basic understanding of calcification established, S. apsteinii could be a valuable model to further study coccolithophore calcification and cell physiological responses to ocean acidification. [ABSTRACT FROM AUTHOR]

A fundamental requirement of all eukaryotes is the ability to translocate protons across membranes. This is critical in bioenergetics, for compartmentalized metabolism, and to regulate intracellular pH (pHi) within a range that is compatible with cellular metabolism. Plants, animals, and algae utilize specialized transport machinery for membrane energization and pH homeostasis that reflects the prevailing ionic conditions in which they evolved. The recent characterization of H+-permeable channels in marine and freshwater algae has led to the discovery of novel functions for these transport proteins in both cellular pH homeostasis and sensory biology. Here we review the potential implications for understanding the origins and evolution of membrane excitability and the phytoplankton-based marine ecosystem responses to ocean acidification. [Copyright &y& Elsevier]

Complex photoreceptor pathways exist in algae to exploit light as a sensory stimulus. Previous studies have implicated calcium in blue-light signaling in plants and algae. A photophobic response to high-intensity blue light was characterized in the marine benthic diatom Navicula perminuta (Grunow) in van Heurck. Calcium modulators were used to determine the involvement of calcium in the signaling of this response, and the fluorescent calcium indicator Calcium Crimson was used to image changes in intracellular [Ca2+] during a response. A localized, transient elevation of Calcium Crimson fluorescence was seen at the cell tip at the time of cell reversal. Intracellular calcium release inhibitors produced a significant decrease in the population photophobic response. Treatments known to decrease influx of extracellular calcium had no effect on the population photophobic response but did cause a significant decrease in average cell speed. As the increase in intracellular [Ca2+] at the cell tip corresponded to the time of direction change rather than the onset of the light stimulus, it would appear that Ca2+ constitutes a component of the switching mechanism that leads to reversal of the locomotion machinery. Our current evidence suggests that the source of this Ca2+ is intracellular. [ABSTRACT FROM AUTHOR]

Marine coccolithophorid phytoplankton are major producers of biogenic calcite, playing a significant role in the global carbon cycle. Predicting the impacts of ocean acidification on coccolithophore calcification has received much recent attention and requires improved knowledge of cellular calcification mechanisms. Uniquely amongst calcifying organisms, coccolithophores produce calcified scales (coccoliths) in an intracellular compartment and secrete them to the cell surface, requiring large transcellular ionic fluxes to support calcification. In particular, intracellular calcite precipitation using HCO3 - as the substrate generates equimolar quantities of H+ that must be rapidly removed to prevent cytoplasmic acidification. We have used electrophysiological approaches to identify a plasma membrane voltage-gated H+ conductance in Coccolithus pelagicus ssp braarudii with remarkably similar biophysical and functional properties to those found in metazoans. We show that both C. pelagicus and Emiliania huxleyi possess homologues of metazoan Hv1 H+ channels, which function as voltagegated H+ channels when expressed in heterologous systems. Homologues of the coccolithophore H+ channels were also identified in a diversity of eukaryotes, suggesting a wide range of cellular roles for the Hv1 class of proteins. Using single cell imaging, we demonstrate that the coccolithophore H+ conductance mediates rapid H+ efflux and plays an important role in pH homeostasis in calcifying cells. The results demonstrate a novel cellular role for voltage gated H+ channels and provide mechanistic insight into biomineralisation by establishing a direct link between pH homeostasis and calcification. As the coccolithophore H+ conductance is dependent on the trans-membrane H+ electrochemical gradient, this mechanism will be directly impacted by, and may underlie adaptation to, ocean acidification. The presence of this H+ efflux pathway suggests that there is no obligate use of H+ derived from calcification for intracellular CO2 generation. Furthermore, the presence of Hv1 class ion channels in a wide range of extant eukaryote groups indicates they evolved in an early common ancestor. [ABSTRACT FROM AUTHOR]

Motility of estuarine epipelic (mud-inhabiting) diatoms is an important adaptation to living in biofilms present within fine sediments. Motility allows cells to migrate within the photic zone in response to a wide range of environmental stimuli. The motile responses of two species of benthic diatoms to photon fluence rates and spectral quality were investigated. Cultures of Navicula perminuta (Grunow) in van Heurck and Cylindrotheca closterium (Ehrenb.) J. C. Lewin et Reimann both exhibited photoaccumulation at ∼200 μmol · m−2 · s−1 and photodispersal from photon flux densities (PFDs) of ∼15 μmol · m−2 · s−1. Photokinesis (changing cell speed) contributed toward photodispersal for both species, and red light (λ = 681–691 nm) was most effective at inducing this process. N. perminuta showed a phototactic (directional) response, with active movement in response to a light gradient. Although this response was exhibited in white light, these directional responses were only elicited by wavelengths from 430 to 510 nm. In contrast, C. closterium did not exhibit phototaxis under any light conditions used in this study. Motile benthic diatoms thus exhibit complex and sophisticated responses to light quantity and quality, involving combinations of photokinesis and phototaxis, which can contribute toward explaining the patterns of large-scale cell movements observed in natural estuarine biofilms. [ABSTRACT FROM AUTHOR]

Background: Electrical impulses in animals play essential roles in co-ordinating an array of physiological functions including movement, secretion, environmental sensing and development. Underpinning many of these electrical signals is a fast Na+- based action potential that has been fully characterised only in cells associated with the neuromuscular systems of multicellular animals. Such rapid action potentials are thought to have evolved with the first metazoans, with cnidarians being the earliest representatives. The present study demonstrates that a unicellular protist, the marine diatom Odontella sinensis, can also generate a fast Na+/Ca2+ based action potential that has remarkably similar biophysical and pharmacological properties to invertebrates and vertebrate cardiac and skeletal muscle cells. Methodology/Principal Findings: The kinetic, ionic and pharmacological properties of the rapid diatom action potential were examined using single electrode current and voltage clamp techniques. Overall, the characteristics of the fast diatom currents most closely resemble those of vertebrate and invertebrate muscle Na+/Ca2+ currents. Conclusions/Significance: This is the first demonstration of voltage-activated Na+ channels and the capacity to generate fast Na+-based action potentials in a unicellular photosynthetic organism. The biophysical and pharmacological characteristics together with the presence of a voltage activated Na+/Ca2+ channel homologue in the recently sequenced genome of the diatom Thalassiosira pseudonana, provides direct evidence supporting the hypothesis that this rapid signalling mechanism arose in ancestral unicellular eukaryotes and has been retained in at least two phylogenetically distant lineages of eukaryotes; opisthokonts and the stramenopiles. The functional role of the fast animal-like action potential in diatoms remains to be elucidated but is likely involved in rapid environmental sensing of these widespread and successful marine protists. [ABSTRACT FROM AUTHOR]

Adhesion of raphid diatoms to surfaces, mediated by the secretion of extracellular polymeric substances (EPS), is an important strategy for growth and survival. Diatom biofilms are also important in the context of biofouling. Diatoms exhibit selectivity in adhering to surfaces, but little is understood about how they perceive the properties of a substratum and translate that perception into altered adhesion properties. In this study, we demonstrate that Seminavis robusta Danielidis et D. G. Mann , like many other pennate diatoms , adheres more strongly to hydrophobic surfaces (such as silicone elastomer foul-release coatings) than to hydrophilic surfaces. To explore the cellular mechanisms that may underlie this selectivity, we tested the hypothesis that diatoms may perceive a hydrophilic surface as unconducive to adhesion through a form of stress response involving nitric oxide (NO) production. Single-cell imaging with the fluorescent indicator DAF-FM DA (4-amino-5-methylamino-2′,7′-difluorofluorescein diacetate), revealed NO levels that were 4-fold higher in cells adhered to a hydrophilic surface (acid-washed glass) compared with a hydrophobic surface (polydimethylsiloxane elastomer, PDMSE). Elevated levels of NO caused by the addition of the NO donor S-nitroso- N-acetylpenicillamine (SNAP) did not affect growth, but cells showed reduced adhesion strength to both glass and PDMSE. Addition of the nitric oxide synthase inhibitor NG-monomethyl-l-arginine (NMMA) caused a small but significant increase in adhesion strength. Overall, the results suggest that NO acts as a signal of the wettability properties of substrata for Seminavis. [ABSTRACT FROM AUTHOR]

The formation and secretion of heterococcoliths by the non-motile life phase of the coccolithophore Coccolithus pelagicus was investigated using electron microscopy and time-lapse bright field imaging. Coccolithogenesis in C. pelagicus exhibited sequential mineralization of single coccoliths in Golgi-derived and nuclear-associated vesicles, a pattern similar to the formation of heterococcoliths in Emiliania huxleyi. Our TEM data show that only on maturation does the single coccolith vesicle migrate away from the nucleus before secretion. A reticular body, distinct from the Golgi body, was also clearly visible at the distal surface of the developing coccolith vesicle, suggesting this is a common structural feature in placolith cells that mineralize and secrete coccoliths one at a time. Time-lapse imaging revealed that the coccolith secretion process is rapid, taking 60-190 seconds, and involves considerable contractile activity to eject and position the coccolith on the surface of the cell. An intact flagellar root apparatus was discovered at the anterior pole of this non-motile cell from which polarized secretion of coccoliths occurs, which may indicate a novel role for such cytoskeletal structures. Freeze-fracture preparations revealed columnar deposits and adhesions linking the scales and coccolith baseplates to the cell, across the periplasmic space providing points of attachment for cellular movement. Rotatory movements of the cell relative to external coccoliths were exhibited by all actively calcifying cells. These movements enable the cell, while exhibiting morphologically polarized secretion, to locate and secrete a mature coccolith in a spatially well-defined manner. Finally, the time-lapse imaging approach described here provides an opportunity to quantify the regulation of coccolith production in single cells with high temporal resolution allowing responses of calcification to rapidly fluctuating environmental conditions such as light-dark transitions to be examined in detail, which has not been possible with bulk calcification studies. [ABSTRACT FROM AUTHOR]

Phytoplankton plasma membrane electron transport activity was determined by monitoring the reduction of the impermeant artificial electron acceptor ferricyanide in a range of diatoms. The results revealed that constitutive plasma membrane electron transport activity of marine diatoms is high compared with chlorophytes and higher plant cells. Diatom plasma membrane electron transport activity was not significantly increased by iron limitation. This lack of induction on iron limitation indicates that diatoms have an iron acquisition strategy that is distinct from chlorophytes and the dicotyledon higher plants that exhibit marked increases in plasma membrane ferricyanide reductase activity on iron limitation. The interaction of the constitutive plasma membrane electron transport with photosynthesis was also investigated. We found that 1) ferricyanide reduction at the plasma membrane was progressively inhibited in response to increasing irradiances; 2) the presence of extracellular ferricyanide, but not the reduced couple ferrocyanide, caused a marked inhibition of carbon fixation at high irradiance; and 3) extracellular electron acceptors ferricyanide and hexachloroiridate (but not ferrocyanide) induced an immediate and reversible decrease in fluorescence yields (Fo and Fm). The extent to which extracellular electron acceptors affected CO2 fixation, Fo, and Fm was related to the level of constitutive ferricyanide reductase activity, the species with highest ferricyanide reduction rates being most sensitive. The data suggest that consumption of electrons and/or reductant at the plasma membrane by external acceptors may compete directly with CO2 fixation for electrons, alter cytosolic-chloroplast redox poise, and/or induce a redox-signaling cascade that alters photosynthetic metabolism. [ABSTRACT FROM AUTHOR]

Microplastics are ubiquitous in marine and estuarine ecosystems, and thus there is increasing concern regarding exposure and potential effects in commercial species. To address this knowledge gap, we investigated the effects of microplastics on larval and early juvenile life stages of the Black Sea Bass (Centropristis striata), a North American fishery. Larvae (13–14 days post hatch, dph) were exposed to 1.0 × 104, 1.0 × 105, and 1.0 × 106 particles L−1 of low-density polyethylene (LDPE) microspheres (10–20 μm) directly in seawater and via trophic transfer from microzooplankton prey (tintinnid ciliates, Favella spp.). We also compared the ingestion of virgin and chemically-treated microspheres incubated with either phenanthrene, a polycyclic aromatic hydrocarbon, or 2,4-di-tert-butylphenol (2,4-DTBP), a plastic additive. Larval fish did not discriminate between virgin or chemically-treated microspheres. However, larvae did ingest higher numbers of microspheres through ingestion of microzooplankton prey than directly from the seawater. Early juveniles (50–60 dph) were directly exposed to the virgin and chemically-treated LDPE microspheres, as well as virgin LDPE microfibers for 96 h to determine physiological effects (i.e., oxygen consumption and immune response). There was a significant positive relationship between oxygen consumption and increasing microfiber concentration, as well as a significant negative relationship between immune response and increasing virgin microsphere concentration. This first assessment of microplastic pollution effects in the early life stages of a commercial finfish species demonstrates that trophic transfer from microzooplankton can be a significant route of microplastic exposure to larval stages of C. striata , and that multi-day exposure to some microplastics in early juveniles can result in physiological stress. [Display omitted] • Larval sea bass ingest more microplastics from ciliate prey than from the water. • Exposure to fibers causes increased oxygen consumption in juvenile sea bass. • Exposure to virgin microspheres decreased immune response in juvenile sea bass. • Presence of phenanthrene or di-tert butyl phenol did not influence ingestion. • Presence of associated chemicals did not affect respiration or immune response. [ABSTRACT FROM AUTHOR]

The recently characterized single-domain voltage-gated ion channels from eukaryotic protists (EukCats) provide an array of novel channel proteins upon which to test the pharmacology of both clinically and environmentally relevant marine toxins. Here, we examined the effects of the hydrophilic µ-CTx PIIIA and the lipophilic brevetoxins PbTx-2 and PbTx-3 on heterologously expressed EukCat ion channels from a marine diatom and coccolithophore. Surprisingly, none of the toxins inhibited the peak currents evoked by the two EukCats tested. The lack of homology in the outer pore elements of the channel may disrupt the binding of µ-CTx PIIIA, while major structural differences between mammalian sodium channels and the C-terminal domains of the EukCats may diminish interactions with the brevetoxins. However, all three toxins produced significant negative shifts in the voltage dependence of activation and steady state inactivation, suggesting alternative and state-dependent binding conformations that potentially lead to changes in the excitability of the phytoplankton themselves. [ABSTRACT FROM AUTHOR]

Coccolithophores are unicellular phytoplankton that are characterized by the presence intricately formed calcite scales (coccoliths) on their surfaces. In most cases coccolith formation is an entirely intracellular process – crystal growth is confined within a Golgi-derived vesicle. A wide range of coccolith morphologies can be found amongst the different coccolithophore groups. This review discusses the cellular factors that regulate coccolith production, from the roles of organic components, endomembrane organization and cytoskeleton to the mechanisms of delivery of substrates to the calcifying compartment. New findings are also providing important information on how the delivery of substrates to the calcification site is co-ordinated with the removal of H + that are a bi-product of the calcification reaction. While there appear to be a number of species-specific features of the structural and biochemical components underlying coccolith formation, the fluxes of Ca 2+ and a HCO 3 − required to support coccolith formation appear to involve spatially organized recruitment of conserved transport processes. [ABSTRACT FROM AUTHOR]

Complex photoreceptor pathways exist in algae to exploit light as a sensory stimulus. Previous studies have implicated calcium in blue-light signaling in plants and algae. A photophobic response to high-intensity blue light was characterized in the marine benthic diatom Navicula perminuta (Grunow) in van Heurck. Calcium modulators were used to determine the involvement of calcium in the signaling of this response, and the fluorescent calcium indicator Calcium Crimson was used to image changes in intracellular [Ca2+] during a response. A localized, transient elevation of Calcium Crimson fluorescence was seen at the cell tip at the time of cell reversal. Intracellular calcium release inhibitors produced a significant decrease in the population photophobic response. Treatments known to decrease influx of extracellular calcium had no effect on the population photophobic response but did cause a significant decrease in average cell speed. As the increase in intracellular [Ca2+] at the cell tip corresponded to the time of direction change rather than the onset of the light stimulus, it would appear that Ca2+ constitutes a component of the switching mechanism that leads to reversal of the locomotion machinery. Our current evidence suggests that the source of this Ca2+ is intracellular. [ABSTRACT FROM AUTHOR]

Rapid Na+/Ca2+-based action potentials govern essential cellular functions in eukaryotes, from the motile responses of unicellular protists, such as Paramecium [ 1, 2 ], to complex animal neuromuscular activity [ 3 ]. A key innovation underpinning this fundamental signaling process has been the evolution of four-domain voltage-gated Na+/Ca2+ channels (4D-Ca v s/Na v s). These channels are widely distributed across eukaryote diversity [ 4 ], albeit several eukaryotes, including land plants and fungi, have lost voltage-sensitive 4D-Ca v /Na v s [ 5–7 ]. Because these lineages appear to lack rapid Na+/Ca2+-based action potentials, 4D-Ca v /Na v s are generally considered necessary for fast Na+/Ca2+-based signaling [ 7 ]. However, the cellular mechanisms underpinning the membrane physiology of many eukaryotes remain unexamined. Eukaryotic phytoplankton critically influence our climate as major primary producers. Several taxa, including the globally abundant diatoms, exhibit membrane excitability [ 8–10 ]. We previously demonstrated that certain diatom genomes encode 4D-Ca v /Na v s [ 4 ] but also proteins of unknown function, resembling prokaryote single-domain, voltage-gated Na+ channels (BacNa v s) [ 4 ]. Here, we show that single-domain channels are actually broadly distributed across major eukaryote phytoplankton lineages and represent three novel classes of single-domain channels, which we refer collectively to as EukCats. Functional characterization of diatom EukCatAs indicates that they are voltage-gated Na+- and Ca2+-permeable channels, with rapid kinetics resembling metazoan 4D-Ca v s/Na v s. In Phaeodactylum tricornutum , which lacks 4D-Ca v /Na v s, EukCatAs underpin voltage-activated Ca2+ signaling important for membrane excitability, and mutants exhibit impaired motility. EukCatAs therefore provide alternative mechanisms for rapid Na+/Ca2+ signaling in eukaryotes and may functionally replace 4D-Ca v s/Na v s in pennate diatoms. Marine phytoplankton thus possess unique signaling mechanisms that may be key to environmental sensing in the oceans. • Novel class of single-domain, voltage-gated channels (EukCatAs) identified in diatoms • EukCatAs are fast voltage-gated Na+- and Ca2+-permeable channels • EukCatAs underpin voltage-activated Ca2+ signaling and membrane excitability • EukCatAs may have functionally replaced 4D-Ca v /Na v channels in pennate diatoms Diatoms exhibit fast animal-like action potentials, but many species lack 4D-Ca v /Na v channels that underpin membrane excitability in animals. Diatoms do encode novel 1D voltage-gated channels (EukCatAs). Helliwell, Chrachri et al. show that EukCatAs are fast Na+ and Ca2+ channels that provide alternative mechanisms for rapid signaling in eukaryotes. [ABSTRACT FROM AUTHOR]

Marine coccolithophores are globally distributed, unicellular phytoplankton that produce nanopatterned, calcite biominerals (coccoliths). These biominerals are synthesized internally, deposited into an extracellular coccosphere, and routinely released into the external medium, where they profoundly affect the global carbon cycle. The cellular costs and benefits of calcification remain unresolved. Here, we show observational and experimental evidence, supported by biophysical modeling, that free coccoliths are highly adsorptive biominerals that readily interact with cells to form chimeric coccospheres and with viruses to form "viroliths," which facilitate infection. Adsorption to cells is mediated by organic matter associated with the coccolith base plate and varies with biomineral morphology. Biomineral hitchhiking increases host-virus encounters by nearly an order of magnitude and can be the dominant mode of infection under stormy conditions, fundamentally altering how we view biomineral-cell-virus interactions in the environment.

Odontocete cetaceans have undergone profound modifications to their integument and sensory systems and are generally thought to lack specialized exocrine glands that in terrestrial mammals function to produce chemical signals (Thewissen & Nummela, 2008). Keenan-Bateman et al. (2016, 2018), though, introduced an enigmatic exocrine gland, associated with the false gill slit pigmentation pattern in Kogia breviceps. These authors provided a preliminary description of this cervical gill slit gland in their helminthological studies of the parasitic nematode, Crassicauda magna. This study offers the first detailed gross and histological description of this gland and reports upon key differences between immature and mature individuals. Investigation reveals it is a complex, compound tubuloalveolar gland with a well-defined duct that leads to a large, and expandable central chamber, which in turn leads to two caudally projecting diverticula. All regions of the gland contain branched tubular and alveolar secretory regions, although most are found in the caudal diverticula, where the secretory process is holocrine. The gland lies between slips of cutaneous muscle, and is innervated by lamellar corpuscles, resembling Pacinian's corpuscles, suggesting that its secretory product may be actively expressed into the environment. Mature K. breviceps display larger gland size, and increased functional activity in glandular tissues, as compared to immature individuals. These results demonstrate that the cervical gill slit gland of K. breviceps shares morphological features of the specialized, chemical signaling, exocrine glands of terrestrial members of the Cetartiodactyla., (© 2021 American Association for Anatomy.)

The evolution of Na + -selective four-domain voltage-gated channels (4D-Na v s) in animals allowed rapid Na + -dependent electrical excitability, and enabled the development of sophisticated systems for rapid and long-range signaling. While bacteria encode single-domain Na + -selective voltage-gated channels (BacNa v ), they typically exhibit much slower kinetics than 4D-Na v s, and are not thought to have crossed the prokaryote-eukaryote boundary. As such, the capacity for rapid Na + -selective signaling is considered to be confined to certain animal taxa, and absent from photosynthetic eukaryotes. Certainly, in land plants, such as the Venus flytrap ( Dionaea muscipula ) where fast electrical excitability has been described, this is most likely based on fast anion channels. Here, we report a unique class of eukaryotic Na + -selective, single-domain channels (EukCatBs) that are present primarily in haptophyte algae, including the ecologically important calcifying coccolithophores, Emiliania huxleyi and Scyphosphaera apsteinii The EukCatB channels exhibit very rapid voltage-dependent activation and inactivation kinetics, and isoform-specific sensitivity to the highly selective 4D-Na v blocker tetrodotoxin. The results demonstrate that the capacity for rapid Na + -based signaling in eukaryotes is not restricted to animals or to the presence of 4D-Na v s. The EukCatB channels therefore represent an independent evolution of fast Na + -based electrical signaling in eukaryotes that likely contribute to sophisticated cellular control mechanisms operating on very short time scales in unicellular algae., (© 2020 American Society of Plant Biologists. All Rights Reserved.)