Comparison of two Phaeodactylum tricornutum ecotypes under nitrogen starvation and resupply reveals distinct lipid accumulation strategies but a common degradation process.

Introduction: Phaeodactylum tricornutum is a model species frequently used to study lipid metabolism in diatoms. When exposed to a nutrient limitation or starvation, diatoms are known to accumulate neutral lipids in cytoplasmic lipid droplets (LDs). Those lipids are produced partly de novo and partly from the recycle of plastid membrane lipids. Under a nitrogen resupply, the accumulated lipids are catabolized, a phenomenon about which only a few data are available. Various strains of P. tricornutum have been isolated around the world that may differ in lipid accumulation patterns. Methods: To get further information on this topic, two genetically distant ecotypes of P. tricornutum (Pt1 and Pt4) have been cultivated under nitrogen deprivation during 11 days followed by a resupply period of 3 days. The importance of cytoplasmic LDs relative to the plastid was assessed by a combination of confocal laser scanning microscopy and cell volume estimation using bright field microscopy pictures. Results and discussion: We observed that in addition to a basal population of small LDs (0.005 µm3 to 0.7 µm3) present in both strains all along the experiment, Pt4 cells immediately produced two large LDs (up to 12 µm3 after 11 days) while Pt1 cells progressively produced a higher number of smaller LDs (up to 7 µm3 after 11 days). In this work we showed that, in addition to intracellular available space, lipid accumulation may be limited by the pre-starvation size of the plastid as a source of membrane lipids to be recycled. After resupplying nitrogen and for both ecotypes, a fragmentation of the largest LDs was observed as well as a possible migration of LDs to the vacuoles that would suggest an autophagic degradation. Altogether, our results deepen the understanding of LDs dynamics and open research avenues for a better knowledge of lipid degradation in diatoms.

Enhancing the biochemical growth of Haematococcus pluvialis by mitigation of broad-spectrum light stress in wastewater cultures.

In this study, the microalgae Haematococcus pluvialis were cultivated in wastewater inoculated into low-density polypropylene plastic air pillows (LDPE-PAPs) under a light stress. The cells were irradiated to different light stresses using white LED lights (WLs) as the control, and broad-spectrum lights (BLs) as a test for the period of 32 days. It was observed that the inoculum (70 × 102 mL-1 cells) of H. pluvialis algal cells increased almost 30 and 40 times in WL and BL, respectively, at day 32 coherent to its biomass productivity. Higher lipid concentration of up to 36.85 µg mL-1 was observed in BL irradiated cells compared to 13.215 µg L-1 dry weight of biomass in WL. The chlorophyll 'a' content was 2.6 times greater in BL (3.46 µg mL-1) compared to that in WL (1.32 µg mL-1) with total carotenoids being about 1.5 times greater in BL compared to WL on day 32. The yield of red pigment 'Astaxanthin' was about 27% greater in BL than in WL. The presence, of different carotenoids including astaxanthin was also confirmed by HPLC, whereas fatty acid methyl esters (FAMEs) were confirmed by GC-MS. This study further confirmed that wastewater alongwith with light stress is suitable for the biochemical growth of H. pluvialis with good biomass yield as well as carotenoid accumulation. Additionally there was 46% reduction in chemical oxygen demand (COD) in a far more efficient manner when cultured in recycled LDPE-PAP. Such type of cultivation of H. pluvialis made the overall process economical and suitable for upscaling to produce value-added products such as lipids, pigments, biomass, and biofuel for commercial applications.

Metal Contamination and Biomarkers in Cerastoderma glaucum: A Multi-level Approach.

In this study, we focused on evaluating the responses of the cockle, Cerastoderma glaucum to in situ exposures to metals at three sites in the Gulf of Gabes in the coastal zone of Tunisia differing in levels of metal contamination. Firstly, we examined the general physiological state of the organisms. Secondly, we evaluated the bioaccumulation of several metals (Cd, Cu, Zn, Ni) in the cockles. Thirdly, we focused on evaluating histologically changes in gametogenesis and sexual maturity of the organisms. Finally, we determined the expression of seven key genes encoding enzymes or proteins involved in responses to different types of environmental stressors. Results showed a decrease in the general physiological status of the cockles, including a reduced condition index, sex ratios skewed to females (70% and 80% females in the intermediate and the contaminated site, respectively) and greater mortalities in tests under anoxic conditions (i.e., stress on stress test) in cockles collected from the most contaminated site (LT50 = 2.88 days) compared to the cockles from the intermediate site (LT50 = 5 days) and the less contaminated site (LT50 = 6 days). Results for metal bioaccumulation showed that the levels of Cd, Cu, Zn and Ni in cockles were consistent with the contaminant gradient, with the highest levels in cockles from the most contaminated site (1.04; 4.92; 52.76 and 13.81 µg/g dw, respectively), followed by those from the intermediate site (0.34; 2.94; 36.94; 17.40 µg/g dw, respectively) and then the less contaminated site (0.065; 1.27; 21.62 and 5.40 µg/g dw, respectively). Results from the gametogenesis and maturity index showed few differences in the reproductive cycle of cockles collected from the three study sites. There were different patterns of gene expression that were divided into three groups in terms of responses: (1) expression of genes involved in metal detoxification, ATP Binding Cassette Subfamily B Member 1 (ABCB1) and metallothionein MT) and genes for superoxide dismutases (i.e., Mn SOD and CuZn SOD), which did not show any difference in their levels of expression; (2) heat shock protein 70 (HSP70) gene expression, which decreased in cockles according to the pollution gradient, and (3) expression of catalase (CAT) and cytochrome oxidase subunit 1 (COI) genes was threefold and 1000-fold higher in cockles from intermediate and most contaminated sites compared to the less contaminated site. Therefore, changes in overall physiological condition, sex ratios and expression of HSP70, CAT and COI genes may be appropriate biomarkers for in situ studies of the impacts of metals in cockles. However, these biomarkers should be coupled to proteomics studies.

Astaxanthin as a King of Ketocarotenoids: Structure, Synthesis, Accumulation, Bioavailability and Antioxidant Properties.

Astaxanthin (3,3-dihydroxy-ß, ß-carotene-4,4-dione) is a ketocarotenoid synthesized by Haematococcus pluvialis/lacustris, Chromochloris zofingiensis, Chlorococcum, Bracteacoccus aggregatus, Coelastrella rubescence, Phaffia rhodozyma, some bacteria (Paracoccus carotinifaciens), yeasts, and lobsters, among others However, it is majorly synthesized by Haematococcus lacustris alone (about 4%). The richness of natural astaxanthin over synthetic astaxanthin has drawn the attention of industrialists to cultivate and extract it via two stage cultivation process. However, the cultivation in photobioreactors is expensive, and converting it in soluble form so that it can be easily assimilated by our digestive system requires downstream processing techniques which are not cost-effective. This has made the cost of astaxanthin expensive, prompting pharmaceutical and nutraceutical companies to switch over to synthetic astaxanthin. This review discusses the chemical character of astaxanthin, more inexpensive cultivating techniques, and its bioavailability. Additionally, the antioxidant character of this microalgal product against many diseases is discussed, which can make this natural compound an excellent drug to minimize inflammation and its consequences.

Bioinformatics-Based Screening Approach for the Identification and Characterization of Lipolytic Enzymes from the Marine Diatom Phaeodactylum tricornutum.

Oleaginous diatoms accumulate lipids of biotechnological interest when exposed to nutrient stress conditions such as nitrogen starvation. While accumulation mechanisms are well-known and have been engineered to improve lipid production, degradation mechanisms remain poorly investigated in diatoms. Identifying lipid-degrading enzymes is the initial step to understanding the catabolic processes. In this study, an in silico screening of the genome of Phaeodactylum tricornutum led to the identification of 57 putative triacylglycerol lipases (EC 3.1.1.3) grouped in 4 families. Further analysis revealed the presence of conserved domains and catalytic residues of lipases. Physico-chemical characteristics and subcellular localization predictions highlighted that a majority of these putative proteins are hydrophilic and cytosolic, suggesting they could be recruited to lipid droplets directly from the cytosol. Among the 57 identified putative proteins, three lipases were identified as possibly involved in lipophagy due to a potential vacuolar localization. The expression of the mRNA corresponding to the 57 proteins was then searched in 3 transcriptomic datasets obtained under nitrogen starvation. Nine genes were highly regulated and were considered as encoding enzymes with a probable important function in lipid catabolism. A tertiary structure prediction of these nine candidates yielded eight functional 3D models. Among those, two downregulated enzymes, Phatr3_J54974 and Phatr3_EG00720, were highlighted as good targets for future functional genomics and purification studies to investigate their role in lipid degradation.

ABSCISIC ACID INSENSITIVE 4 coordinates eoplast formation to ensure acquisition of seed longevity during maturation in Medicago truncatula.

Seed longevity, the capacity to remain alive during dry storage, is pivotal to germination performance and is essential for preserving genetic diversity. It is acquired during late maturation concomitantly with seed degreening and the de-differentiation of chloroplasts into colorless, non-photosynthetic plastids, called eoplasts. As chlorophyll retention leads to poor seed performance upon sowing, these processes are important for seed vigor. However, how these processes are regulated and connected to the acquisition of seed longevity remains poorly understood. Here, we show that such a role is at least provided by ABSCISIC ACID INSENSITIVE 4 (ABI4) in the legume Medicago truncatula. Mature seeds of Mtabi4 mutants contained more chlorophyll than wild-type seeds and exhibited a 75% reduction in longevity and reduced dormancy. MtABI4 was necessary to stimulate eoplast formation, as evidenced by the significant delay in the dismantlement of photosystem II during the maturation of mutant seeds. Mtabi4 seeds also exhibited transcriptional deregulation of genes associated with retrograde signaling and transcriptional control of plastid-encoded genes. Longevity was restored when Mtabi4 seeds developed in darkness, suggesting that the shutdown of photosynthesis during maturation, rather than chlorophyll degradation per se, is a requisite for the acquisition of longevity. Indeed, the shelf life of stay green mutant seeds that retained chlorophyll was not affected. Thus, ABI4 plays a role in coordinating the dismantlement of chloroplasts during seed development to avoid damage that compromises the acquisition of seed longevity. Analysis of Mtabi4 Mtabi5 double mutants showed synergistic effects on chlorophyll retention and longevity, suggesting that they act via parallel pathways.

Sustainable treatment of dye wastewater by recycling microalgal and diatom biogenic materials: Biorefinery perspectives.

Discharge of untreated or partially treated toxic dyes containing wastewater from textile industries into water streams is hazardous for environment. The use of heavy metal(s) rich dyes, which are chemically active in azo and sulfur content(s) has been tremendously increasing in last two decades. Conventional physical and chemical treatment processes help to eliminate the dyes from textile wastewater but generates the secondary pollutants which create an additional environmental problem. Microalgae especially the diatoms are promising candidate for dye remediation from textile wastewater. Nanoporous diatoms frustules doped with nanocomposites increase the wastewater remediation efficiency due to their adsorption properties. On the other hand, microalgae with photosynthetic microbial fuel cell have shown significant results in being efficient, cost effective and suitable for large scale phycoremediation. This integrated system has also capability to enhance lipid and carotenoids biosynthesis in microalgae while simultaneously generating the bioelectricity. The present review highlights the textile industry wastewater treatment by live and dead diatoms as well as microalgae such as Chlorella, Scenedesmus, Desmodesmus sp. etc. This review engrosses applicability of diatoms and microalgae as an alternative way of conventional dye removal techniques with techno-economic aspects.

A techno-economic approach for eliminating dye pollutants from industrial effluent employing microalgae through microbial fuel cells: Barriers and perspectives.

Microbial fuel cells are biochemical factories which besides recycling wastewater are electricity generators, if their low power density can be scaled up. This also adds up to work on many factors responsible to increase the cost of running a microbial fuel cell. As a result, the first step is to use environment friendly dead organic algae biomass or even living algae cells in a microbial fuel cell, also referred to as microalgal microbial fuel cells. This can be a techno-economic aspect not only for treating textile wastewater but also an economical way of obtaining value added products and bioelectricity from microalgae. Besides treating wastewater, microalgae in its either form plays an essential role in treating dyes present in wastewater which essentially include azo dyes rich in synthetic ions and heavy metals. Microalgae require these metals as part of their metabolism and hence consume them throughout the integration process in a microbial fuel cell. In this review a detail plan is laid to discuss the treatment of industrial effluents (rich in toxic dyes) employing microbial fuel cells. Efforts have been made by researchers to treat dyes using microbial fuel cell alone or in combination with catalysts, nanomaterials and microalgae have also been included. This review therefore discusses impact of microbial fuel cells in treating wastewater rich in textile dyes its limitations and future aspects.

Perovskite-based solar cells fabricated from TiO2 nanoparticles hybridized with biomaterials from mollusc and diatoms.

Perovskite solar cells (PVSCs) convert solar energy into electrical energy. Current study employs fabrication of PVSCs using calcium titanate (CaTiO3) prepared by co-precipitation of TiO2 nanoparticle (NP) and CaCO3 NP with later synthesized from mollusc shell. Furthermore, frustules of diatom, Nitzschia palea were used to prepare silica doped CaTiO3 (Si-CaTiO3) nanocomposite. CaTiO3 NP and Si-CaTiO3 nanocomposites film were made on fluorine doped tin oxide (FTO) glass plate using spin coater separately for two different kinds of PVSCs tested at different intensities of light. The perovskite materials were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM) and energy dispersive X-ray (EDX) spectroscopy. Thickness of the film was measured by profilometer. The maximum power density (PDmax) of CaTiO3 made PVSCs was 0.235 mW/m2 under white LED light and 0.041 mW/m2 in broad spectrum light. Whereas, PDmax of PVSCs with Si-CaTiO3 was higher about 0.0083 mW/m2 in broad spectrum light and was 0.0039 mW/m2 in white LED light. This is due to the fact that CaTiO3 allowed blue and red light in broad spectrum to pass through it without being absorbed compared to white LED light which gets reflected. On the offset, in PVSC made of Si-CaTiO3 since diatoms frustules are made up of nanoporous architecture it increases the overall porosity of PVSC making them potentially more efficient in broad spectrum of light compared to white LED light.

Impact of light on microalgal photosynthetic microbial fuel cells and removal of pollutants by nanoadsorbent biopolymers: Updates, challenges and innovations.

Photosynthetic microbial fuel cells (PMFCs) with microalgae have huge potential for treating wastewater while simultaneously converting light energy into electrical energy. The efficiency of such cells directly depends on algal growth, which depends on light intensity. Higher light intensity results in increased potential as well as enhancement in generation of biomass rich in biopolymers. Such biopolymers are produced either by microbes at anode and algae at cathode or vice versa. The biopolymers recovered from these biological sources can be added in wastewater alone or in combination with nanomaterials to act as nanoadsorbents. These nanoadsorbents further increase the efficiency of PMFC by removing the pollutants like metals and dyes. In this review firstly the effect of different light intensities on the growth of microalgae, importance of diatoms in a PMFC and their impact on PMFCs efficiencies have been narrated. Secondly recovery of biopolymers from different biological sources and their role in removal of metals, dyes along with their impact on circular bioeconomy have been discussed. Thereafter bottlenecks and future perspectives in this field of research have been narrated.

Resilience of bumblebee foraging behavior despite colony size reduction.

Foraging behavior is driven by diverse factors, notably life history traits. Foraging strategies are particularly complex among eusocial species such as bumblebees, because they depend primarily on the needs of the colony, rather than on individual's needs. Colony size, i.e. the number of workers in a colony vary a lot among eusocial insects. While a large colony can be adaptive, several drivers can strongly decrease colony size, like pesticides or high temperatures. In this study, we used the bumblebee Bombus terrestris to assess if workers adapted their foraging behavior to such rapid decreases in colony size. We conducted the foraging experiments with two plant species commonly used by bumblebees: Borago officinalis and Echium plantagineum. Several foraging parameters were measured: foraging time, number of foraging trips, number of workers foraging, handling time and visiting rate. Despite a drastic reduction in colony size, nearly all the foraging behavior parameters were unaffected by the colony size reduction. Colonies that were subject to a large decrease in workers instead displayed high resilience and behavioral plasticity by quickly increasing the proportion of foragers. Ultimately, further research should assess if this consistency in foraging behavior also allows bumblebee colonies to maintain both the efficiency of the resources collection and pollination.

Metabolite Quantification by Fourier Transform Infrared Spectroscopy in Diatoms: Proof of Concept on Phaeodactylum tricornutum.

Diatoms are feedstock for the production of sustainable biocommodities, including biofuel. The biochemical characterization of newly isolated or genetically modified strains is seminal to identify the strains that display interesting features for both research and industrial applications. Biochemical quantification of organic macromolecules cellular quotas are time-consuming methodologies which often require large amount of biological sample. Vibrational spectroscopy is an essential tool applied in several fields of research. A Fourier transform infrared (FTIR) microscopy-based imaging protocol was developed for the simultaneous cellular quota quantification of lipids, carbohydrates, and proteins of the diatom Phaeodactylum tricornutum. The low amount of sample required for the quantification allows the high throughput quantification on small volume cultures. A proof of concept was performed (1) on nitrogen-starved experimental cultures and (2) on three different P. tricornutum wild-type strains. The results are supported by the observation in situ of lipid droplets by confocal and brightfield microscopy. The results show that major differences exist in the regulation of lipid metabolism between ecotypes of P. tricornutum.

Diatom microalgae as smart nanocontainers for biosensing wastewater pollutants: recent trends and innovations.

Microalgae have been recognized as one of the most efficient microorganisms to remediate industrial effluents. Among microalgae diatoms are silica shelled unicellular eukaryotes, found in all types of water bodies and flourish very well even in wastewater. They have their silica cell wall made up of nano arrayed pores arranged in a uniform fashion. Therefore, they act as smart nanocontainers to adsorb various trace metals, dyes, polymers, and drugs which are hazardous to human as well to aquatic life. The beautiful nanoarchitecture in diatoms allows them to easily bind to ligands of choice to form a nanocomposite structure with the pollutants which can be a chemical or biological component. Such naturally available diatom nanomaterials are economical and highly sensitive compared to manmade artificial silica nanomaterials to help in facile removal of the toxic pollutants from wastewater. This review is thus focused on employing diatoms to remediate various pollutants such as heavy metals, dyes, hydrocarbons detected in the wastewater. It also includes different microalgae as biosensors for determination of pollutants in effluents and the perspectives for nanotechnological applications in the field of remediating pollutants through microalgae. The review also discusses in length the hurdles and perspectives of employing microalgae in wastewater remediation.

"Light modulates transcriptomic dynamics upregulating astaxanthin accumulation in Haematococcus: A review".

Haematococcus pluvialis is a green alga that can accumulate high astaxanthin content, a commercially demanding market keto food. Due to its high predicted market value of about 3.4 billion USD in 2027, it is essential to increase its production. Therefore, it is crucial to understand the genetic mechanism and gene expressions profile during astaxanthin synthesis. The effect of poly- and mono-chromatic light of different wavelengths and different intensities have shown to influence the gene expression towards astaxanthin production. This includes transcriptomic gene analysis in H. pluvialis underneath different levels of illumination stress. This review has placed the most recent data on the effects of light on bioastaxanthin production in the context of previous studies, which were more focused on the biochemical and physiological sides. Doing so, it contributes to delineate new ways along the biotechnological process with the aim to increase bioastaxanthin production while decreasing production costs.

The Transition Toward Nitrogen Deprivation in Diatoms Requires Chloroplast Stand-By and Deep Metabolic Reshuffling.

Microalgae have adapted to face abiotic stresses by accumulating energy storage molecules such as lipids, which are also of interest to industries. Unfortunately, the impairment in cell division during the accumulation of these molecules constitutes a major bottleneck for the development of efficient microalgae-based biotechnology processes. To address the bottleneck, a multidisciplinary approach was used to study the mechanisms involved in the transition from nitrogen repletion to nitrogen starvation conditions in the marine diatom Phaeodactylum tricornutum that was cultured in a turbidostat. Combining data demonstrate that the different steps of nitrogen deficiency clustered together in a single state in which cells are in equilibrium with their environment. The switch between the nitrogen-replete and the nitrogen-deficient equilibrium is driven by intracellular nitrogen availability. The switch induces a major gene expression change, which is reflected in the reorientation of the carbon metabolism toward an energy storage mode while still operating as a metabolic flywheel. Although the photosynthetic activity is reduced, the chloroplast is kept in a stand-by mode allowing a fast resuming upon nitrogen repletion. Altogether, these results contribute to the understanding of the intricate response of diatoms under stress.

Application of pulsed electric fields for the biocompatible extraction of proteins from the microalga Haematococcus pluvialis.

This study aims to employ a pulsed electric field (PEF) treatment for the biocompatible (non-destructive) extraction of proteins from living cells of the green microalga Haematococcus pluvialis. Using a field strength of 1 kV cm-1, we achieved the extraction of 10.2 µg protein per mL of culture, which corresponded to 46% of the total amount of proteins that could be extracted by complete destructive extraction (i.e. the grinding of biomass with glass beads). We found that the extraction yield was not improved by stronger field strengths and was not dependent on the pulse frequency. A biocompatibility index (BI) was defined as the relative abundance of cells that remained alive after the PEF treatment. This index relied on measurements of several physiological parameters after a PEF treatment. It was found that at 1 kV cm-1 that cultures recovered after 72 h. Therefore, these PEF conditions constituted a good compromise between protein extraction efficiency and culture survival. To characterize the PEF treatment further at a molecular level, mass spectrometry-based proteomics analyses of PEF-prepared extracts was used. This led to the identification of 52 electro-extracted proteins. Of these, only 16 proteins were identified when proteins were extracted with PEF at 0.5 cm-1. They belong to core metabolism, stress response and cell movement. Unassigned proteins were also extracted. Their physiological implications and possible utilization in food as alimentary complements are discussed.

Transcriptomic Response of Breast Cancer Cells MDA-MB-231 to Docosahexaenoic Acid: Downregulation of Lipid and Cholesterol Metabolism Genes and Upregulation of Genes of the Pro-Apoptotic ER-Stress Pathway.

Despite considerable efforts in prevention and therapy, breast cancer remains a major public health concern worldwide. Numerous studies using breast cancer cell lines have shown the antiproliferative and pro-apoptotic effects of docosahexaenoic acid (DHA). Some studies have also demonstrated the inhibitory effect of DHA on the migration and invasion of breast cancer cells, making DHA a potential anti-metastatic agent. Thus, DHA has shown its potential as a chemotherapeutic adjuvant. However, the molecular mechanisms triggering DHA effects remain unclear, and the aim of this study was to provide a transcriptomic basis for further cellular and molecular investigations. Therefore, MDA-MB-231 cells were treated with 100 µM DHA for 1`2 h or 24 h before RNA-seq analysis. The results show the great impact of DHA-treatment on the transcriptome, especially after 24 h of treatment. The impact of DHA is particularly visible in genes involved in the cholesterol biosynthesis pathway that is strongly downregulated, and the endoplasmic reticulum (ER)-stress response that is, conversely, upregulated. This ER-stress and unfolded protein response could explain the pro-apoptotic effect of DHA. The expression of genes related to migration and invasion (especially SERPINE1, PLAT, and MMP11) is also impacted by DHA. In conclusion, this transcriptomic analysis supports the antiproliferative, pro-apoptotic and anti-invasive effects of DHA, and provides new avenues for understanding its molecular mechanisms.

Carbon Orientation in the Diatom Phaeodactylum tricornutum: The Effects of Carbon Limitation and Photon Flux Density.

Diatoms adapt to changing environmental conditions in very efficient ways. Among the mechanisms that can be activated, the reorientation of carbon metabolism is crucial because it allows the storage of energy into energy-dense molecules, typically lipids. Beside their roles in physiology, lipids are commercially interesting compounds. Therefore studies dealing with this topic are relevant for both basic and applied science. Although the molecular mechanisms involved in the reorientation of carbon metabolism as a response to a deficiency in nutrients such as nitrogen or phosphorus has been partially elucidated, the impacts of carbon availability on the implementation of the reorientation mechanisms remain unclear. Indeed, it has not been determined if the same types of mechanisms are activated under carbon and other nutrient deficiencies or limitations. The first aim of this work was to get insights into the physiological, biological and molecular processes triggered by progressive carbon starvation in the model diatom Phaeodactylum tricornutum. The second aim was to investigate the effects of the growth light intensity on these processes. For such a purpose three different photon flux densities 30, 300, and 1000 µmol photons m-2 s-1 were used. The results presented here demonstrate that under carbon limitation, diatom cells still reorient carbon metabolism toward either phosphoenolpyruvate or pyruvate, which serves as a hub for the production of more complex molecules. The distribution of carbon atoms between the different pathways was partially affected by the growth photon flux density because low light (LL) provides conditions for the accumulation of chrysolaminarin, while medium light mostly stimulated lipid synthesis. A significant increase in the amount of proteins was observed under high light (HL).

Effects of Hg sublethal exposure in the brain of peacock blennies Salaria pavo: Molecular, physiological and histopathological analysis.

Marine environments are affected by large amounts of toxicants among those mercury (Hg). The aim of this study was to assess potential neurotoxic effects of Hg in the peacock blenny Salaria pavo. A sublethal contamination to 66 µg HgCl2 L-1 over periods of 1, 4, 10 and 15 days was performed. Total Hg concentrations measured in the brain highlighted the detection of Hg at days 1 and 4 following the exposure but no concentration of the metal was further detected. Partial-length cDNA of genes coding ABC transporters (abcb1, abcc1, abcc2, abcg2) and acetylcholinesterase (ache) were characterized. Results from mRNA expression levels displayed an up-regulation of abcb1 mRNA while a down-regulation of abcc1 and abcc2 mRNA was observed. No change in abcg2 and ache mRNA expression was noted throughout the experiment. At each sampling time, Hg exposure did not affect the activity of the AChE enzyme. The histological analysis indicated that fish exhibited several damages in the optic tectum and the cerebellum and 3 reaction patterns were identified for each organ: circulatory disturbances, regressive and progressive changes. Molecular, physiological and histological biomarkers assessed in the present study highlighted that peacock blennies were able to detoxify Hg from the brain tissue by developing defense mechanisms. More globally, neurotoxic effects of a sublethal Hg exposure in the brain of peacock blennies and the adaptation capacity of this species were evaluated.