Diatom teratologies as biomarkers of contamination: Are all deformities ecologically meaningful?

Contaminant-related stress on aquatic biota is difficult to assess when lethal impacts are not observed. Diatoms, by displaying deformities (teratologies) in their valves, have the potential to reflect sub-lethal responses to environmental stressors such as metals and organic compounds. For this reason, there is great interest in using diatom morphological aberrations in biomonitoring. However, the detection and mostly the quantification of teratologies is still a challenge; not all studies have succeeded in showing a relationship between the proportion of abnormal valves and contamination level along a gradient of exposure. This limitation in part reflects the loss of ecological information from diatom teratologies during analyses when all deformities are considered. The type of deformity, the severity of aberration, species proneness to deformity formation, and propagation of deformities throughout the population are key components and constraints in quantifying teratologies. Before a metric based on diatom deformities can be used as an indicator of contamination, it is important to better understand the “ecological signal” provided by this biomarker. Using the overall abundance of teratologies has proved to be an excellent tool for identifying contaminated and non-contaminated environments (presence/absence), but refining this biomonitoring approach may bring additional insights allowing for a better assessment of contamination level along a gradient. The dilemma: are all teratologies significant, equal and/or meaningful in assessing changing levels of contamination? This viewpoint article examines numerous interrogatives relative to the use of diatom teratologies in water quality monitoring, provides selected examples of differential responses to contamination, and proposes solutions that may refine our understanding and quantification of the stress. This paper highlights the logistical problems associated with accurately evaluating and interpreting teratologies and stimulates more discussion and research on the subject to enhance the sensitivity of this metric in bioassessments

Diatom Deformities and Tolerance to Cadmium Contamination in Four Species

The relative tolerance of four diatoms (Nitzschia palea, Pinnularia mesolepta, Mayamaea atomus, and Gomphonema truncatum) to Cd was evaluated, including their proneness to deformities, and the severity of the abnormalities in relation to Cd concentration. The indirect effect of Cd on photosynthetic capacities was assessed during a short time exposure experiment using a dose-response approach to evaluate the relative tolerance of the four diatom species. The EC25 were 9 (3, 23), 606 (348, 926), 1179 (1015, 1349) and 2394 (1890, 2896) µg/L for P. mesolepta, G. truncatum, N. palea, and M. atomus respectively. P. mesolepta was by far the most Cd sensitive species while M. atomus was the most tolerant. In addition, diatoms were exposed to a single concentration of Cd comparable to a heavily contaminated environment for a longer duration to evaluate the effect of Cd on growth kinetics and the deformities induced. N. palea, P. mesolepta, and M. atomus were able to grow when cultivated with Cd while G. truncatum was not. Cadmium strongly affected the effective quantum yield in G. truncatum (4.8 ± 5.9% of the control) and P. mesolepta cultures (29.2 ± 6.9% of the control). The effects were moderate for N. palea (88.3 ± 0.7% of the control) and no impact was observed for M. atomus. The results from the two approaches were in accordance since they identified N. palea and M. atomus as the two most tolerant species to Cd, while P. mesolepta and G. truncatum were the most sensitive. The microscopy analyses revealed that P. mesolepta was more impacted by Cd than N. palea and M. atomus considering both the quantity of abnormal cells and the severity of the deformities. Overall, this research shows that not all deformities can be considered equal for a water quality bio-assessment. The work highlights a need to take into account metal-tolerance/sensitivity of the species and the severity of the deformities

Insights into the Diversity of Secondary Metabolites of Planktothrix Using a Biphasic Approach Combining Global Genomics and Metabolomics

Cyanobacteria are an ancient lineage of slow-growing photosynthetic bacteria and a prolific source of natural products with diverse chemical structures and potent biological activities and toxicities. The chemical identification of these compounds remains a major bottleneck. Strategies that can prioritize the most prolific strains and novel compounds are of great interest. Here, we combine chemical analysis and genomics to investigate the chemodiversity of secondary metabolites based on their pattern of distribution within some cyanobacteria. Planktothrix being a cyanobacterial genus known to form blooms worldwide and to produce a broad spectrum of toxins and other bioactive compounds, we applied this combined approach on four closely related strains of Planktothrix. The chemical diversity of the metabolites produced by the four strains was evaluated using an untargeted metabolomics strategy with high-resolution LC–MS. Metabolite profiles were correlated with the potential of metabolite production identified by genomics for the different strains. Although, the Planktothrix strains present a global similarity in terms of a biosynthetic cluster gene for microcystin, aeruginosin, and prenylagaramide for example, we found remarkable strain-specific chemodiversity. Only few of the chemical features were common to the four studied strains. Additionally, the MS/MS data were analyzed using Global Natural Products Social Molecular Networking (GNPS) to identify molecular families of the same biosynthetic origin. In conclusion, we depict an efficient, integrative strategy for elucidating the chemical diversity of a given genus and link the data obtained from analytical chemistry to biosynthetic genes of cyanobacteria

Effets de mélanges de pesticides sur les biofilms périphytiques d'eau douce

On considère généralement les biofilms comme des indicateurs biologiques d’alerte, les organismes les composant ayant des temps de génération relativement courts et présentant une grande diversité de preferenda environnementaux et de sensibilité aux altérations anthropiques. Dans ces travaux, les effets de pesticides sur les biofilms de rivière ont été étudiés à différentes échelles de représentativité, allant de mélanges complexes à faible dose en utilisant des extraits d’échantillonneur passif POCIS (Polar Organic Chemical Integrative Sampler) à des molécules testées seules, en passant par des mélanges simples.L’exposition chronique et à faible dose aux extraits de POCIS a révélé des impacts au niveau de la croissance, de la structure (assemblages de diatomées) et du fonctionnement du biofilm en lien avec son exposition passée. De plus les expériences utilisant des molécules testées seules (pesticides et métabolites) et les mélanges simples ont permis de caractériser la toxicité relative des composés présents dans les extraits de POCIS en lien avec leur mode d’action et d’explorer la réponse de descripteurs encore peu utilisés en écotoxicologie comme la construction de Rapid Light Curves (RLCs).Ce travail confirme la pertinence de l’utilisation des extraits d’échantillonneurs passifs comme le POCIS pour mieux appréhender les effets des pesticides en mélanges sur le biofilm de rivière ainsi que l’intérêt des RLCs en tant que descripteur précoces d’exposition aux pesticides.Biofilms can be regarded as biological warming systems, because they are generally composed of short generation time organisms presenting a large range of environmental preferenda and various sensibilities to anthropogenic disturbance. In the present study, effects of pesticides on river biofilms have been studied at different levels of representativeness, from complex mixtures at low dose represented by POCIS passive sampler extracts (Polar Organic Chemical Integrative Sampler) to molecules tested alone via simple mixtures.Chronic exposure to low dose of POCIS extracts revealed impacts on growth related, structural (diatom assemblages) and functional parameters related to biofilm exposure history. Moreover experiment using single molecules and simple mixtures allowed to characterised the relative toxicity of compounds present in the POCIS extracts in link with their specific mode of action and explore the response of descriptor not very used in ecotoxicology field like the construction of Rapid Light Curves (RLCs).This work confirms the relevance of the use of passive sampler extracts as POCIS in order to better understand the effects of pesticides in mixture on river biofilms as well as the interest of RLCs as early exposure descriptors of pesticides exposure

Improving toxicity assessment of pesticide mixtures: the use of polar passive sampling devices extracts in microalgae toxicity tests

Complexity of contaminants exposure needs to be taking in account for an appropriate evaluation of risks related to mixtures of pesticides released in the ecosystems. Toxicity assessment of such mixtures can be made through a variety of toxicity tests reflecting different level of biological complexity. This paper reviews the recent developments of passive sampling techniques for polar compounds, especially Polar Organic Chemical Integrative Samplers (POCIS) and Chemcatcher® and the principal assessment techniques using microalgae in laboratory experiments. The progresses permitted by the coupled use of such passive samplers and ecotoxicology testing as well as their limitations are presented. Case studies combining passive sampling devices (PSD) extracts and toxicity assessment toward microorganisms at different biological scales from single organisms to communities level are presented. These case studies, respectively aimed i) at characterizing the toxic potential of waters using dose-response curves, and ii) at performing microcosm experiments with increased environmental realism in the toxicant exposure in term of cocktail composition and concentration. Finally perspectives and limitations of such approaches for future applications in the area of environmental risk assessment are discussed

Effets de mélanges réalistes de pesticides sur des communautés naturelles périphytiques ayant différentes histoires d'exposition

International audienceThis study deals with the use of Polar Organic Chemical Integrative Sampler (POCIS) extracts to assess the impact of low-dose pesticide mixtures on natural biofilm communities originating from either a chronically contaminated or a reference field site. To investigate how natural biofilm communities, pre-exposed to pesticides in situ or not might respond to environmentally realistic changes in pesticide pressure, they were exposed to either clean water or to POCIS extracts (PE) in order to represent toxic pressure with a realistic pesticide mixture directly isolated from the field. The impacts of PE were assessed on structure, physiology and growth of biofilms. Initial levels of tolerance of phototrophic communities to PE were also estimated at day 0. PE exposure led to negative effects on diatom growth kinetics independently of in-field biofilm exposure history. In contrast, the impacts observed on dry weight, ash-free dry mass and algal fluorescence-related parameters followed different trends depending on biofilm origin. Exposure to PE induced changes in diatom assemblages for the biofilm originating from the reference field site with higher relative abundance of Eolimna minima and Nitzschia palea with PE exposure. Initial tolerance of phototrophic communities to PE was 8-fold higher for the biofilm originating from the chronically contaminated site compared to the reference field site. The use of POCIS extracts allowed us to highlight both chronic impacts of low doses of a mixture of pesticides on natural communities with regard to biofilm exposure history as well as initial levels of tolerance of phototrophic communities

Genomic Insights of <i>Alnus</i>-Infective <i>Frankia</i> Strains Reveal Unique Genetic Features and New Evidence on Their Host-Restricted Lifestyle

The present study aimed to use comparative genomics to explore the relationships between Frankia and actinorhizal plants using a data set made of 33 Frankia genomes. The determinants of host specificity were first explored for “Alnus-infective strains” (i.e., Frankia strains belonging to Cluster Ia). Several genes were specifically found in these strains, including an agmatine deiminase which could possibly be involved in various functions as access to nitrogen sources, nodule organogenesis or plant defense. Within “Alnus-infective strains”, Sp+ Frankia genomes were compared to Sp− genomes in order to elucidate the narrower host specificity of Sp+ strains (i.e., Sp+ strains being capable of in planta sporulation, unlike Sp− strains). A total of 88 protein families were lost in the Sp+ genomes. The lost genes were related to saprophytic life (transcriptional factors, transmembrane and secreted proteins), reinforcing the proposed status of Sp+ as obligatory symbiont. The Sp+ genomes were also characterized by a loss of genetic and functional paralogs, highlighting a reduction in functional redundancy (e.g., hup genes) or a possible loss of function related to a saprophytic lifestyle (e.g., genes involved in gas vesicle formation or recycling of nutrients)

Dynamics of the Metabolome of <i>Aliinostoc</i> sp. PMC 882.14 in Response to Light and Temperature Variations

Cyanobacteria are microorganisms able to adapt to a wide variety of environmental conditions and abiotic stresses. They produce a large number of metabolites that can participate in the dynamic adaptation of cyanobacteria to a range of different light, temperature, and nutrient conditions. Studying the metabolite profile is one way to understand how the physiological status of cells is related to their adaptive response. In this study, we sought to understand how the diversity and dynamics of the whole metabolome depended on the growth phase and various abiotic factors such as light intensity and temperature. The cyanobacterium, Aliinostoc sp. PMC 882.14, was selected for its large number of biosynthetic gene clusters. One group of cells was grown under normal conditions as a control, while other groups were grown under higher light or temperature. Metabolomes were analyzed by mass spectrometry (qTOF-MS/MS) combined with untargeted analysis to investigate metabolite dynamics, and significant variation was found between exponential and stationary phases, regardless of culture conditions. In the higher light group, the synthesis of several metabolites, including shinorine, was induced while other metabolites, such as microviridins, were synthesized under higher temperature conditions. Among highly regulated metabolites, we observed the presence of mycosporine-like amino acids (MAAs) and variants of somamides, microginins, and microviridins. This study demonstrated the importance of considering the physiological state of cyanobacteria for comparative global metabolomics and studies of the regulatory processes involved in production of specific metabolites. Our results also open up new perspectives on the use of organisms such as cyanobacteria for the targeted production of bioactive metabolites

Pesticide toxicity towards microalgae increases with environmental mixture complexity

International audienceEffect-directed analysis (EDA) aims at identifying the compound(s) responsible for toxicity in a complex environmental sample where several dozens of contaminants can be present. In this study, we used an environmental mixture extracted from the Polar Organic Chemical Integrative Sampler (POCIS) previously immersed downstream a landfill (River Ponteils, South West France), to perform an EDA approach using a microalgal bioassay based on the photosynthetic capacities of diatom (Nitzschia palea) cultures. Adverse effects on photosynthetic capacities were recorded when algae were exposed to the entire POCIS extract (> 85% inhibition at the highest concentration tested). This result was coherent with the detection of diuron and isoproturon, which were the 2 most concentrated herbicides in the extract. However, the EDA process did not allow pointing out the specific compound(s) responsible for the observed toxicity but rather suggested that multiple compounds were involved in the overall toxicity and caused mixture effects

Insights into the Diversity of Secondary Metabolites of Planktothrix Using a Biphasic Approach Combining Global Genomics and Metabolomics

International audienceCyanobacteria are an ancient lineage of slow-growing photosynthetic bacteria and a prolific source of natural products with diverse chemical structures and potent biological activities and toxicities. The chemical identification of these compounds remains a major bottleneck. Strategies that can prioritize the most prolific strains and novel compounds are of great interest. Here, we combine chemical analysis and genomics to investigate the chemodiversity of secondary metabolites based on their pattern of distribution within some cyanobacteria. Planktothrix being a cyanobacterial genus known to form blooms worldwide and to produce a broad spectrum of toxins and other bioactive compounds, we applied this combined approach on four closely related strains of Planktothrix. The chemical diversity of the metabolites produced by the four strains was evaluated using an untargeted metabolomics strategy with high-resolution LC-MS. Metabolite profiles were correlated with the potential of metabolite production identified by genomics for the different strains. Although, the Planktothrix strains present a global similarity in terms of a biosynthetic cluster gene for microcystin, aeruginosin, and prenylagaramide for example, we found remarkable strain-specific chemodiversity. Only few of the chemical features were common to the four studied strains. Additionally, the MS/MS data were analyzed using Global Natural Products Social Molecular Networking (GNPS) to identify molecular families of the same biosynthetic origin. In conclusion, we depict an efficient, integrative strategy for elucidating the chemical diversity of a given genus and link the data obtained from analytical chemistry to biosynthetic genes of cyanobacteria. Key Contribution: The chemodiversity of Planktothrix metabolites revealed by genome mining and molecular networking