Collective intercellular communication through ultra-fast hydrodynamic trigger waves.

The biophysical relationships between sensors and actuators1-5 have been fundamental to the development of complex life forms. Swimming organisms generate abundant flows that persist in aquatic environments6-13, and responding promptly to external stimuli is key to survival14-19. Here we present the discovery of 'hydrodynamic trigger waves' in cellular communities of the protist Spirostomum ambiguum that propagate-in a manner similar to a chain reaction20-22-hundreds of times faster than their swimming speed. By coiling its cytoskeleton, Spirostomum can contract its long body by 60% within milliseconds23, experiencing accelerations that can reach forces of 14g. We show that a single cellular contraction (the transmitter) generates long-ranged vortex flows at intermediate Reynolds numbers that can, in turn, trigger neighbouring cells (the receivers). To measure the sensitivity to hydrodynamic signals in these receiver cells, we present a high-throughput suction-flow device for probing mechanosensitive ion channels24 by back-calculating the microscopic forces on the cell membrane. We analyse and quantitatively model the ultra-fast hydrodynamic trigger waves in a universal framework of antenna and percolation theory25,26, and reveal a phase transition that requires a critical colony density to sustain collective communication. Our results suggest that this signalling could help to organize cohabiting communities over large distances and influence long-term behaviour through gene expression (comparable to quorum sensing16). In more immediate terms, because contractions release toxins27, synchronized discharges could facilitate the repulsion of large predators or immobilize large prey. We postulate that numerous aquatic organisms other than protists could coordinate their behaviour using variations of hydrodynamic trigger waves.

Widespread transmission of independent cancer lineages within multiple bivalve species.

Most cancers arise from oncogenic changes in the genomes of somatic cells, and while the cells may migrate by metastasis, they remain within that single individual. Natural transmission of cancer cells from one individual to another has been observed in two distinct cases in mammals (Tasmanian devils and dogs), but these are generally considered to be rare exceptions in nature. The discovery of transmissible cancer in soft-shell clams (Mya arenaria) suggested that this phenomenon might be more widespread. Here we analyse disseminated neoplasia in mussels (Mytilus trossulus), cockles (Cerastoderma edule), and golden carpet shell clams (Polititapes aureus) and find that neoplasias in all three species are attributable to independent transmissible cancer lineages. In mussels and cockles, the cancer lineages are derived from their respective host species; however, unexpectedly, cancer cells in P. aureus are all derived from Venerupis corrugata, a different species living in the same geographical area. No cases of disseminated neoplasia have thus far been found in V. corrugata from the same region. These findings show that transmission of cancer cells in the marine environment is common in multiple species, that it has originated many times, and that while most transmissible cancers are found spreading within the species of origin, cross-species transmission of cancer cells can occur.

Energetic coupling between plastids and mitochondria drives CO2 assimilation in diatoms.

Diatoms are one of the most ecologically successful classes of photosynthetic marine eukaryotes in the contemporary oceans. Over the past 30 million years, they have helped to moderate Earth's climate by absorbing carbon dioxide from the atmosphere, sequestering it via the biological carbon pump and ultimately burying organic carbon in the lithosphere. The proportion of planetary primary production by diatoms in the modern oceans is roughly equivalent to that of terrestrial rainforests. In photosynthesis, the efficient conversion of carbon dioxide into organic matter requires a tight control of the ATP/NADPH ratio which, in other photosynthetic organisms, relies principally on a range of plastid-localized ATP generating processes. Here we show that diatoms regulate ATP/NADPH through extensive energetic exchanges between plastids and mitochondria. This interaction comprises the re-routing of reducing power generated in the plastid towards mitochondria and the import of mitochondrial ATP into the plastid, and is mandatory for optimized carbon fixation and growth. We propose that the process may have contributed to the ecological success of diatoms in the ocean.

Additions to the genus Gimesia: description of Gimesia alba sp. nov., Gimesia algae sp. nov., Gimesia aquarii sp. nov., Gimesia aquatilis sp. nov., Gimesia fumaroli sp. nov. and Gimesia panareensis sp. nov., isolated from aquatic habitats of the Northern Hemisphere.

Thirteen novel planctomycetal strains were isolated from five different aquatic sampling locations. These comprise the hydrothermal vent system close to Panarea Island (Italy), a biofilm on the surface of kelp at Monterey Bay (CA, USA), sediment and algae on Mallorca Island (Spain) and Helgoland Island (Germany), as well as a seawater aquarium in Braunschweig, Germany. All strains were shown to belong to the genus Gimesia. Their genomes cover a size range from 7.22 to 8.29 Mb and have a G+C content between 45.1 and 53.7%. All strains are mesophilic (Topt 26-33 °C) with generation times between 12 and 32 h. Analysis of fatty acids yielded palmitic acid (16:0) and a fatty acid with the equivalent chain length of 15.817 as major compounds. While five of the novel strains belong to the already described species Gimesia maris and Gimesia chilikensis, the other strains belong to novel species, for which we propose the names Gimesia alba (type strain Pan241wT = DSM 100744T = LMG 31345T = CECT 9841T = VKM B-3430T), Gimesia algae (type strain Pan161T = CECT 30192T = STH00943T = LMG 29130T), Gimesia aquarii (type strain V144T = DSM 101710T = VKM B-3433T), Gimesia fumaroli (type strain Enr17T = DSM 100710T = VKM B-3429T) and Gimesia panareensis (type strain Enr10T = DSM 100416T = LMG 29082T). STH numbers refer to the Jena Microbial Resource Collection (JMRC).

Visualizing virus assembly intermediates inside marine cyanobacteria.

Cyanobacteria are photosynthetic organisms responsible for ∼25% of organic carbon fixation on the Earth. These bacteria began to convert solar energy and carbon dioxide into bioenergy and oxygen more than two billion years ago. Cyanophages, which infect these bacteria, have an important role in regulating the marine ecosystem by controlling cyanobacteria community organization and mediating lateral gene transfer. Here we visualize the maturation process of cyanophage Syn5 inside its host cell, Synechococcus, using Zernike phase contrast electron cryo-tomography (cryoET). This imaging modality yields dramatic enhancement of image contrast over conventional cryoET and thus facilitates the direct identification of subcellular components, including thylakoid membranes, carboxysomes and polyribosomes, as well as phages, inside the congested cytosol of the infected cell. By correlating the structural features and relative abundance of viral progeny within cells at different stages of infection, we identify distinct Syn5 assembly intermediates. Our results indicate that the procapsid releases scaffolding proteins and expands its volume at an early stage of genome packaging. Later in the assembly process, we detected full particles with a tail either with or without an additional horn. The morphogenetic pathway we describe here is highly conserved and was probably established long before that of double-stranded DNA viruses infecting more complex organisms.

Workshop report: Cryopreservation of aquatic biomedical models.

The genetic resources of aquatic biomedical model organisms are the products of millions of years of evolution, decades of scientific development, and hundreds of millions of dollars of research funding investment. Genetic resources (e.g., specific alleles, transgenes, or combinations) of each model organism can be considered a form of scientific wealth that can be accumulated and exchanged, typically in the form of live animals or germplasm. Large-scale maintenance of live aquatic organisms that carry these genetic resources is inefficient, costly, and risky. In situ maintenance may be substantially enhanced and backed up by combining cryopreserved germplasm repositories and genetic information systems with live animal culture. Unfortunately, cryopreservation has not advanced much beyond the status of an exploratory research for most aquatic species, lacks widespread application, and methods for successful cryopreservation remain poorly defined. For most aquatic species biological materials other than sperm or somatic cells are not comprehensively banked to represent and preserve a broad range of genetic diversity for each species. Therefore, new approaches and standardization are needed for repository-level application to ensure reproducible recovery of cryopreserved materials. Additionally, development of new technologies is needed to address preservation of novel biological materials, such as eggs and embryos of aquatic species. To address these goals, the Office of Research Infrastructure Programs (ORIP) of the National Institutes of Health (NIH) hosted the Cryopreservation of Aquatic Biomedical Models Workshop on January 7 to 8, 2017, in conjunction with the 8th Aquatic Animal Models of Human Disease Conference in Birmingham, Alabama. The goals of the workshop were to assess the status of germplasm cryopreservation in various biomedical aquatic models and allow representatives of the scientific community to develop and prioritize a consensus of specific actionable recommendations that will move the field of cryopreservation of aquatic resources forward. This workshop included sessions devoted to new approaches for cryopreservation of aquatic species, discussion of current efforts and approaches in preservation of aquatic model germplasm, consideration of needs for standardization of methods to support reproducibility, and enhancement of repository development by establishment of scalable high-throughput technologies. The following three broad recommendations were forwarded from workshop attendees: 1: Establish a comprehensive, centralized unit ("hub") to programmatically develop training for and documentation of cryopreservation methods for aquatic model systems. This would include development of species-specific protocols and approaches, outreach programs, community development and standardization, freezing services and training of the next generation of experts in aquatic cryopreservation. 2: Provide mechanisms to support innovative technical advancements that will increase the reliability, reproducibility, simplicity, throughput, and efficiency of the cryopreservation process, including vitrification and pipelines for sperm, oocytes, eggs, embryos, larvae, stem cells, and somatic cells of all aquatic species. This recommendation encompasses basic cryopreservation knowledge and engineering technology, such as microfluidics and automated processing technologies. 3: Implement mechanisms that allow the various aquatic model stock centers to increase their planning, personnel, ability to secure genetic resources and to promote interaction within an integrated, comprehensive repository network for aquatic model species repositories.

Establishment and activity of the D quadrant organizer in the marine gastropod Crepidula fornicata.

During development in metazoan embryos, the fundamental embryonic axes are established by organizing centers that influence the fates of nearby cells. Among the spiralians, a large and diverse branch of protostome metazoans, studies have shown that an organizer sets up the dorsal-ventral axis, which arises from one of the four basic cell quadrants during development (the dorsal, D quadrant). Studies in a few species have also revealed variation in terms of how and when the D quadrant and the organizer are established. In some species the D quadrant is specified conditionally, via cell-cell interactions, while in others it is specified autonomously, via asymmetric cell divisions (such as those involving the formation of polar lobes). The third quartet macromere (3D) typically serves as the spiralian organizer; however, other cells born earlier or later in the D quadrant lineage can serve as the organizer, such as the 2d micromere in the annelid Capitella teleta or the 4d micromere in the mollusc Crepidula fornicata. Here we present work carried out in the snail C. fornicata to show that establishment of a single D quadrant appears to rely on a combination of both autonomous (via inheritance of the polar lobe) and conditional mechanisms (involving induction via the progeny of the first quartet micromeres). Through systematic ablation of cells, we show that D quadrant identity is established between 5th and 6th cleavage stages, as it is in other spiralians that use conditional specification. Subsequently, following the next cell cycle, organizer activity takes place soon after the birth of the 4d micromere. Therefore, unlike the case in other spiralians that use conditional specification, the specification of the D quadrant and the activity of the dorso-ventral organizer are temporally and spatially uncoupled. We also present data on organizer function in naturally-occurring and experimentally-induced twin embryos, which possess multiple D quadrants. We show that supernumerary D quadrants can arise in C. fornicata (either spontaneously or following polar lobe removal); when multiple D quadrants are present these do not exhibit effective organizer activity. We conclude that the polar lobe is not required for D quadrant specification, though it could play a role in effective organizer activity. We also tested whether the inheritance of the small polar lobe by the D quadrant is associated with the ability to laterally inhibit neighboring quadrants by direct contact in order to normally prevent supernumerary organizers from arising. Finally, we discuss the variation of spiralian organizers in a phylogenetic context.

Formation of the 'Great Unconformity' as a trigger for the Cambrian explosion.

The transition between the Proterozoic and Phanerozoic eons, beginning 542 million years (Myr) ago, is distinguished by the diversification of multicellular animals and by their acquisition of mineralized skeletons during the Cambrian period. Considerable progress has been made in documenting and more precisely correlating biotic patterns in the Neoproterozoic-Cambrian fossil record with geochemical and physical environmental perturbations, but the mechanisms responsible for those perturbations remain uncertain. Here we use new stratigraphic and geochemical data to show that early Palaeozoic marine sediments deposited approximately 540-480 Myr ago record both an expansion in the area of shallow epicontinental seas and anomalous patterns of chemical sedimentation that are indicative of increased oceanic alkalinity and enhanced chemical weathering of continental crust. These geochemical conditions were caused by a protracted period of widespread continental denudation during the Neoproterozoic followed by extensive physical reworking of soil, regolith and basement rock during the first continental-scale marine transgression of the Phanerozoic. The resultant globally occurring stratigraphic surface, which in most regions separates continental crystalline basement rock from much younger Cambrian shallow marine sedimentary deposits, is known as the Great Unconformity. Although Darwin and others have interpreted this widespread hiatus in sedimentation on the continents as a failure of the geologic record, this palaeogeomorphic surface represents a unique physical environmental boundary condition that affected seawater chemistry during a time of profound expansion of shallow marine habitats. Thus, the formation of the Great Unconformity may have been an environmental trigger for the evolution of biomineralization and the 'Cambrian explosion' of ecologic and taxonomic diversity following the Neoproterozoic emergence of animals.

Filamentous bacteria transport electrons over centimetre distances.

Oxygen consumption in marine sediments is often coupled to the oxidation of sulphide generated by degradation of organic matter in deeper, oxygen-free layers. Geochemical observations have shown that this coupling can be mediated by electric currents carried by unidentified electron transporters across centimetre-wide zones. Here we present evidence that the native conductors are long, filamentous bacteria. They abounded in sediment zones with electric currents and along their length they contained strings with distinct properties in accordance with a function as electron transporters. Living, electrical cables add a new dimension to the understanding of interactions in nature and may find use in technology development.

Sheldon spectrum and the plankton paradox: two sides of the same coin-a trait-based plankton size-spectrum model.

The Sheldon spectrum describes a remarkable regularity in aquatic ecosystems: the biomass density as a function of logarithmic body mass is approximately constant over many orders of magnitude. While size-spectrum models have explained this phenomenon for assemblages of multicellular organisms, this paper introduces a species-resolved size-spectrum model to explain the phenomenon in unicellular plankton. A Sheldon spectrum spanning the cell-size range of unicellular plankton necessarily consists of a large number of coexisting species covering a wide range of characteristic sizes. The coexistence of many phytoplankton species feeding on a small number of resources is known as the Paradox of the Plankton. Our model resolves the paradox by showing that coexistence is facilitated by the allometric scaling of four physiological rates. Two of the allometries have empirical support, the remaining two emerge from predator-prey interactions exactly when the abundances follow a Sheldon spectrum. Our plankton model is a scale-invariant trait-based size-spectrum model: it describes the abundance of phyto- and zooplankton cells as a function of both size and species trait (the maximal size before cell division). It incorporates growth due to resource consumption and predation on smaller cells, death due to predation, and a flexible cell division process. We give analytic solutions at steady state for both the within-species size distributions and the relative abundances across species.

Sperm viability assessment in marine invertebrates by fluorescent staining and spectrofluorimetry: A promising tool for assessing marine pollution impact.

The viability of spermatozoa is a crucial parameter to evaluate their quality that is an important issue in ecotoxicological studies. Here, a new method has been developed to rapidly determine the viability of spermatozoa in three marine invertebrates: the ascidian Ciona intestinalis, the sea urchin Paracentrotus lividus and the mollusc Mytilus galloprovincialis. This method employed the dual DNA fluorescent staining coupled with spectrofluorimetric analysis. The dual fluorescent staining used the SYBR-14 stained live spermatozoa and propidium iodide stained degenerated cells that had lost membrane integrity. Stain uptake was assessed by confocal microscopy and then the percentage of live and dead spermatozoa was quantified by spectrofluorimetric analysis. The microscopic examination revealed three populations of spermatozoa: living-SYBR-14 stained, dead-PI stained, and dying-doubly stained spermatozoa. The fluorescence emission peak values recorded in a spectrofluorimeter provide the portion of live and dead spermatozoa showing a significant negative correlation. The stain combination was further validated using known ratios of live and dead spermatozoa. The present study demonstrated that the dual DNA staining with SYBR-14 and propidium iodide was effective in assessing viability of spermatozoa in marine invertebrates and that spectrofluorimetric analysis can be successfully employed to evaluate the percentage of live and dead spermatozoa. The method develop herein is simple, accurate, rapid, sensitive, and cost-effective, so it could be a useful tool by which marine pollutants may be screened for spermiotoxicity.

Lulworthia atlantica: a new species supported by molecular phylogeny and morphological analysis.

This study presents morphological and molecular evidence for the establishment of a new species of Lulworthia based on the evaluation of 11 isolates of Lulworthiales collected in two marinas on the west coast of Portugal initially classified as Lulworthia sp. Maximum likelihood and Bayesian methods were applied to obtain phylogenetic trees for 18S-28S and internal transcribed spacer (ITS1-5.8S-ITS2 = internal transcribed spacer [ITS]) nuc rDNA. The isolates consistently grouped together in a distinct and highly supported clade; all other Lulworthiales analyzed, including the available sequences of Lulworthia spp., segregated separately. These results were supported by common and distinctive morphological characters and enabled recognition and description of the new species Lulworthia atlantica. Two Portuguese isolates were confirmed as Lulworthia cf. purpurea, and two were confirmed as asexual morphs of Zalerion maritima.

Energy cost and putative benefits of cellular mechanisms modulating buoyancy in aflagellate marine phytoplankton.

Little information is available on the energetics of buoyancy modulation in aflagellate phytoplankton, which comprises the majority of autotrophic cells found in the ocean. Here, we computed for three aflagellate species of marine phytoplankton (Emiliania huxleyi, Thalassiosira pseudonana, and Ethmodiscus rex) the theoretical minimum energy cost as photons absorbed and nitrogen resource required of the key physiological mechanisms (i.e., replacement of quaternary ammonium by dimethyl-sulfoniopropionate, storage of polysaccharides, and cell wall biosynthesis) affecting the cell's vertical movement as a function of nitrogen (N) availability. These energy costs were also normalized to the capacity of each buoyancy mechanism to modulate sinking or rising rates based on Stokes' law. The three physiological mechanisms could act as ballast in the three species tested in conditions of low N availability at a low fraction (<12%) of the total photon energy cost for growth. Cell wall formation in E. huxleyi was the least costly ballast strategy, whereas in T. pseudonana, the photon energy cost of the three ballast strategies was similar. In E. rex, carbohydrate storage and mobilization appear to be energetically cheaper than modulations in organic solute synthesis to achieve vertical migration. This supports the carbohydrate-ballast strategy for vertical migration for this species, but argues against the theory of replacement of low- or high-density organic solutes. This study brings new insights into the energy cost and potential selective advantages of several strategies modulating the buoyancy of aflagellate marine phytoplankton.

Calcium signaling and endoplasmic reticulum dynamics during fertilization in marine protostome worms belonging to the phylum Nemertea.

Metaphase-I-arrested eggs of marine protostome worms in the phylum Nemertea generate a series of point-source calcium waves during fertilization. Such calcium oscillations depend on inositol-1,4,5-trisphosphate-mediated calcium release from endoplasmic reticulum (ER) stores that undergo structural reorganizations prior to and after fertilization. This article reviews fertilization-induced calcium transients and ER dynamics in nemertean eggs and compares these topics to what has been reported for other animals in order to identify unifying characteristics and distinguishing features of calcium responses during fertilization across the animal kingdom.

Different iron sources to study the physiology and biochemistry of iron metabolism in marine micro-algae.

We compared ferric EDTA, ferric citrate and ferrous ascorbate as iron sources to study iron metabolism in Ostreococcus tauri, Phaeodactlylum tricornutum and Emiliania huxleyi. Ferric EDTA was a better iron source than ferric citrate for growth and chlorophyll levels. Direct and indirect experiments showed that iron was much more available to the cells when provided as ferric citrate as compared to ferric EDTA. As a consequence, growth media with iron concentration in the range 1-100 nM were rapidly iron-depleted when ferric citrate-but not ferric EDTA was the iron source. When cultured together, P. tricornutum cells overgrew the two other species in iron-sufficient conditions, but E. huxleyi was able to compete other species in iron-deficient conditions, and when iron was provided as ferric citrate instead of ferric EDTA, which points out the critical influence of the chemical form of iron on the blooms of some phytoplankton species. The use of ferric citrate and ferrous ascorbate allowed us to unravel a kind of regulation of iron uptake that was dependent on the day/night cycles and to evidence independent uptake systems for ferrous and ferric iron, which can be regulated independently and be copper-dependent or independent. The same iron sources also allowed one to identify molecular components involved in iron uptake and storage in marine micro-algae. Characterizing the mechanisms of iron metabolism in the phytoplankton constitutes a big challenge; we show here that the use of iron sources more readily available to the cells than ferric EDTA is critical for this task.

Phenotypic switching in biofilm-forming marine bacterium Paenibacillus lautus NE3B01.

Biofilm-forming marine bacterium Paenibacillus lautus NE3B01 was isolated from a mangrove ecosystem, Odisha, India. This isolate formed a swarming type of colony pattern on the solid culture medium with 0.5-2 % agar. Phase contrast microscopy study of a growing colony of P. lautus on solid media and swarming pattern revealed the existence of two phenotypically distinct cells (i.e. cocci and rods) across the colonies. However, in actively growing planktonic culture, only rod-shaped cells were observed. Biofilm growth studies (crystal violet assay) with the isolate showed significant biofilm formation by 6 h, and the detachment phase was observed after 18 h. Biofilm parameters (such as total biomass, roughness coefficient, biofilm thickness, etc.) of 24-h-old P. lautus biofilm were studied by confocal scanning laser microscopy (CSLM). The CSLM study showed that P. lautus formed a biofilm with an average thickness of 14.8 ± 2.6 µm, a high roughness coefficient (0.379 ± 0.103) and surface to bio-volume ratio (4.59 ± 1.12 µm(2)/µm(3)), indicating a highly uneven topography of the biofilm. This also indicates that the 24-h-old biofilm is in dispersal phase. Scanning electron microphotographs of P. lautus also supported the existence of two distinct phenotypes of P. lautus. The current findings suggest that P. lautus has two vegetative phenotypes and to decongest the overcrowded biofilm the bacterium can switch over to motile rods from nonmotile cocci and vice versa.

Identification of G protein-coupled receptor signaling pathway proteins in marine diatoms using comparative genomics.

BACKGROUND: The G protein-coupled receptor (GPCR) signaling pathway plays an essential role in signal transmission and response to external stimuli in mammalian cells. Protein components of this pathway have been characterized in plants and simpler eukaryotes such as yeast, but their presence and role in unicellular photosynthetic eukaryotes have not been determined. We use a comparative genomics approach using whole genome sequences and gene expression libraries of four diatoms (Pseudo-nitzschia multiseries, Thalassiosira pseudonana, Phaeodactylum tricornutum and Fragilariopsis cylindrus) to search for evidence of GPCR signaling pathway proteins that share sequence conservation to known GPCR pathway proteins. RESULTS: The majority of the core components of GPCR signaling were well conserved in all four diatoms, with protein sequence similarity to GPCRs, human G protein α- and ß-subunits and downstream effectors. There was evidence for the Gγ-subunit and thus a full heterotrimeric G protein only in T. pseudonana. Phylogenetic analysis of putative diatom GPCRs indicated similarity but deep divergence to the class C GPCRs, with branches basal to the GABAB receptor subfamily. The extracellular and intracellular regions of these putative diatom GPCR sequences exhibited large variation in sequence length, and seven of these sequences contained the necessary ligand binding domain for class C GPCR activation. Transcriptional data indicated that a number of the putative GPCR sequences are expressed in diatoms under various stress conditions in culture, and that many of the GPCR-activated signaling proteins, including the G protein, are also expressed. CONCLUSIONS: The presence of sequences in all four diatoms that code for the proteins required for a functional mammalian GPCR pathway highlights the highly conserved nature of this pathway and suggests a complex signaling machinery related to environmental perception and response in these unicellular organisms. The lack of evidence for some GPCR pathway proteins in one or more of the diatoms, such as the Gγ-subunit, may be due to differences in genome completeness and genome coverage for the four diatoms. The high divergence of putative diatom GPCR sequences to known class C GPCRs suggests these sequences may represent another, potentially ancestral, subfamily of class C GPCRs.

Effects of phthalates on marine organisms: cytotoxicity and genotoxicity of mono-(2-ethylhexyl)-phthalate (MEHP) on European sea bass (Dicentrarchus labrax) embryonic cell line.

INTRODUCTION: Mono-(2-ethylhexyl) phthalate (MEHP) represents a toxicological risk for marine organisms due to its widespread presence in aquatic environments. METHODS: MEHP effects on cell viability, cell death and genotoxicity were investigated on the DLEC cell line, derived from early embryos of the European sea bass Dicentrarchus labrax L. RESULTS: A dose-dependent cytotoxic effect, with no induction of necrotic process, except at its highest concentration, was observed. Moreover, chromosomal instability was detected, both in binucleated and mononucleated cells, coupled with a minor inhibition of cell proliferation, whereas genomic instability was not revealed. To our knowledge, the overall results suggest the first evidence of a possible aneugenic effect of this compound in the DLEC cell line, that is the induction of chromosomal loss events without the induction of primary DNA damage. CONCLUSIONS: MEHP should be considered more harmful than its parent compound DEHP, because it induces genomic instability in the DLEC cell line without triggering cell death.

Weak organic ligands enhance zinc uptake in marine phytoplankton.

A recent study of the effect of pH on Zn and Cd bioavailability shows that binding to weak organic ligands can increase the pool of metals available to phytoplankton in the presence of strong chelating agents. We explore the underlying mechanism in laboratory experiments with the model species Emiliania huxleyi and Thalassiosira weissflogii. Additions of L- and D- isomers of cysteine (Cys) result in similar increases in Zn uptake rates in the presence of the strong chelator ethylenediaminetetraacetic acid (EDTA) but decrease it in the absence of EDTA, ruling out uptake by a specific Zn-Cys transporter. The effect of Cys does not result from alleviating diffusion limitation of inorganic Zn. The enhancement of Zn uptake kinetics by weak ligands is consistent with a mechanism involving formation of a transient ternary complex with uptake molecules: (1) the enhancement is most dramatic in Zn limited cells whose high affinity transporters should be most effective at extracting Zn from weak ligands; (2) the enhancement occurs with a variety of weak ligands, demonstrating that the underlying mechanism has little chemical specificity; and (3) no enhancement of uptake is seen when Zn is bound in complexes that would make formation of multiligand complexes with uptake molecules difficult. Weak complexing agents which have received heretofore little attention may play a key role in the bioavailability of metals in natural waters.