In vivo estimation of pigment composition and optical absorption cross-sectionby spectroradiometry in four aquatic photosynthetic micro-organisms

International audienceThe objective of the present study was to estimate in vivo pigment composition and to retrieve absorption cross-section values, a∗, of photosynthetic micro-organisms using a non-invasive technique of reflectance spectrometry. To test the methodology, organisms from different taxonomical groups and different pigment composition were used (Spirulina platensis a Cyanophyta, Porphyridium cruentum a Rhodophyta, Dunaliella tertiolecta a Chlorophyta and Entomoneis paludosa a Bacillariophyta) and photoacclimated to two different irradiance levels: 25 μmol photon m−2 s−1 (Low Light, LL) and 500 μmol photon m−2 s−1 (High Light, HL). Second derivative spectra from reflectance were used to identify pigment in vivo absorption bands that were linked to specific pigments detected by high performance liquid chromatography. Whereas some absorption bands such as those induced by Chlorophyll (Chl) a (416, 440, 625 and around 675 nm) were ubiquous, others were taxonomically specific (e.g. 636 nm for Chl c in E. paludosa) and/or photo-physiological dependent (e.g. 489 nm for zeaxanthin in the HL-acclimated S. platensis). The optical absorption cross-section, a∗, was retrieved from reflectance data using a radiative transfer model previously developed for microphytobenthos. Despite the cellular Chl a decrease observed from LL to HL (up to 88% for S. platensis), the a∗ increased, except for P. cruentum. This was attributed to a ‘package effect’ and to a greater absorption by photoprotective carotenoids that did not contribute to the energy transfer to the core Chl a

Metadata standards and practical guidelines for specimen and DNA curation when building barcode reference libraries for aquatic life

DNA barcoding and metabarcoding is increasingly used to effectively and precisely assess and monitor biodiversity in aquatic ecosystems. As these methods rely on data availability and quality of barcode reference libraries, it is important to develop and follow best practices to ensure optimal quality and traceability of the metadata associated with the reference barcodes used for identification. Sufficient metadata, as well as vouchers, corresponding to each reference barcode must be available to ensure reliable barcode library curation and, thereby, provide trustworthy baselines for downstream molecular species identification. This document (1) specifies the data and metadata required to ensure the relevance, the accessibility and traceability of DNA barcodes and (2) specifies the recommendations for DNA harvesting and for the storage of both voucher specimens/samples and barcode data.info:eu-repo/semantics/publishedVersio

Editorial: Advances and challenges in microphytobenthos research : from cell biology to coastal ecosystem function

Thanks are due to FCT/MCTES for the financial support to CESAM (UIDP/50017/2020 + UIDB/50017/2020), through national funds, to JS, and to the NERC Blue-coast project to DMP (NE/N016009/1).Publisher PDFPeer reviewe

Typification of the first recognized blue pigmented diatom, Haslea ostrearia (Bacillariophyceae)

Background and aims – The blue pigmented diatom, Haslea ostrearia (Gaillon) Simonsen, which has been the material object for many physiological and ecological studies, was first described from oyster ponds in France as Vibrio ostrearius Gaillon; however, his study material seems not to be conserved.Methods – A thorough search to retrieve potential available historical collections has been conducted.Key results – It has been proven that no relevant historical material exists for H. ostrearia. Thus, an oyster pond at Bouin in Baie de Bourgneuf, France, was sampled in 2018 to obtain material allowing neotype designation.Conclusion – Slides and stubs have been deposited as neotype material of the species in the Muséum National d’Histoire Naturelle, Paris, France (PC). At the same time, this material is the generitype of the genus Haslea Simonsen. Furthermore, isoneotypes have been deposited at the British Museum (BM) and the Bremerhaven Hustedt collection (BRM)

The Vertical Migratory Rhythm of Intertidal Microphytobenthos in Sediment Depends on the Light Photoperiod, Intensity, and Spectrum: Evidence for a Positive Effect of Blue Wavelengths

International audienceEstuarine intertidal flats strong biological productivity is mainly based on the activity of benthic microalgae communities or microphytobenthos (MPB), mostly dominated by diatoms. Epipelon is a major MPB growth form comprising motile species, which perform repeated "vertical migration" patterns in the upper sediment layers according to tidal and diurnal cycles with upward migration at the beginning of the daylight emersion and downward migration before immersion starts. Although this fascinating behavior has been extensively studied for more than a century, many of its features remain uncharacterized. Epipelon migratory rhythms are believed to be driven by an endogenous internal clock of unknown nature in combination with diverse environmental stimuli. Among the environmental stimuli impacting on MPB vertical migration, light is probably the most important. Rhythmic changes in surface abundance of natural MPB assemblages were therefore continuously assessed at high frequency by Imaging-PAM fluorimetry in fresh sediment sampled at different seasons, comprising 85 migration profiles from 40 sediment samplings over 2 years, and exposed to different light conditions without any other environmental stimuli (i.e., no tidal-like water flow and stable optimal temperature). In particular, we manipulated (i) the 24-h natural photoperiod MPB that was acclimated to in order to disentangle the tight link between the diurnal and tidal rhythmicity of epipelon migration, and (ii) the light spectrum in order to potentially influence MPB accumulation at the surface of sediment. We found that the migration rhythmicity mapped onto the tidal cycle but that it was modulated, and even overridden, by the diurnal cycle and by the irradiance level during daytime periods with a positive phototactic upward migration up to a certain threshold (in our conditions, 120 µmol photons m −2 s −1 of white light). Also, we found blue wavelengths (465 nm) triggered MPB surface accumulation, as compared to other wavelengths (white, green, and red) in patterns that were intensity-dependent and species-dependent. In particular, we foundtwo species, Navicula spartinetensis and Gyrosigma fasciola, which strongly migrate up under blue light and could potentially be used as model species for further studying the light-responses of intertidal MPB

Functional xanthophyll cycle and pigment content of a kleptoplastic benthic foraminifer: Haynesina germanica

International audienceSome shallow water benthic foraminifera are able to retain functional chloroplasts (kleptoplasts) from their food source, i.e. diatoms. Here we assessed the functionality of the kleptoplast xanthophyll cycle (XC, i.e. the main diatom short-term photo-regulation mechanism) and we surveyed Haynesina germanica kleptoplast pigment composition over time and at different light regimes. Six common diatom lipophilic pigments were detected, two chlorophylls (Chl a, Chl c) and four carotenoids (fucoxanthin and by-products, diadinoxanthin, diatoxanthin and β-carotene), the same pigment profile as the diatom species frequently isolated at the sampling site. The xanthophyll cycle (XC) was functional with kleptoplast diatoxanthin (DT) content increase with concomitant diadinoxanthin (DD) decrease after short term light exposure. DT/(DT+DD) and DT/DD ratios increased significantly in specimens exposed to low light and high light in comparison to specimens maintained in the dark. Specimens placed in very low light after the light treatments reverted to values close to the initial ones, suggesting that H. germanica XC is functional. A functional XC is an indication of H. germanica kleptoplasts capacity for short-term photo-protection from photo-oxidative damages caused by excess of light. Furthermore, the pigment survey suggests that H. germanica preserved some chloroplasts over a longer time than others and that pigment content is influenced by previous light history. Finally, the current study highlighted seasonal differences, with higher pigment contents in winter specimens (27.35 ± 1.30 ng cell-1) and lower in summer specimens (6.08 ± 1.21 ng cell-1), a quantitative and qualitative composition suggesting light acclimation to low or high light availability, according to the season.</p

Exploration of the bioactive lipids diversity of the marine benthic diatoms of the Nantes Culture Collection (NCC)

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Lipids in benthic diatoms: A new suitable screening procedure

The selection of suitable and indigenous microalgae species is a fundamental requirement in developing added-value bioactive compounds recoverable in the food, health, and cosmetics markets. In this work, an integrated screening approach was developed to characterize the lipid rate of 33 diatom species (including 15 species studied for the first time) belonging to 16 genera from the Nantes Culture Collection, with the main objective of discovering bioactive lipid producers. For that purpose, a simple reliable method for establishing growth kinetics of strains and semi-quantitative analysis of lipid rates was developed. Growth kinetics measurements were achieved by daily minimal measurement fluorescence (F0) whereas lipid rate analyses were performed by high-throughput Fourier Transform Infrared spectroscopy on entire cells and lipid extracts. Results indicated that the method could be used directly on entire cells in spite of the presence of silica for the FTIR approach (due to frustule). The total lipid rate was species-dependant and ranged from 3.7% to 30.5% DW. Six strains out of 33 were found to present a higher total lipid rate superior to 15% DW, and 11 showed medium lipid rates ranging from 10% to 15% DW. The results revealed that five diatom species i.e. Amphora sp. NCC169, Nitzschia sp. NCC109, Nitzschia alexandrina NCC33, Opephora sp. NCC366 and Staurosira sp. NCC182 presented interesting growth capabilities and should be further investigated as potential sources for their original lipid rate

Combined effect of high light and high salinity on the regulation of photosynthesis in three diatom species belonging to the main growth forms of intertidal flat inhabiting microphytobenthos

International audienceThe strong biological production of estuarine intertidal flats is mainly supported by benthic diatoms in temperate areas. Their photosynthetic productivity is largely driven by changes in light intensity and temperature at the surface of sediment flats during emersion. The impact of an increase in salinity of the upper-layer sediment pore-water during emersion, which is often coupled with high light (HL), has been less studied. Furthermore, benthic diatoms show several growth forms which inhabit specific sediment types where the pore-water salinity can differentially vary due to the degree of cohesion of sediment grains. So far, no study explored if the main growth forms of benthic diatoms (i.e. epipelon, epipsammon and tychoplankton) show different photophysiological response to a combine high salinity-HL stress. Based on field monitoring, we compared the photophysiology (photosynthetic efficiency and photoprotection) of three representatives of the main growth forms during a short high salinity coupled with a moderate HL stress and stable optimal temperature, i.e. experimental conditions reproducing Spring environmental conditions in intertidal flats by the Atlantic French coast. Our results show that all growth forms reacted to HL exposure alone, as expected. While the epipelon representative was relatively insensitive to high salinity alone and combined with HL, the tychoplankton representative was highly sensitive to both, and the epipsammon representative was sensitive mainly to the stress combination. These specific responses fitted well with i) their natural habitat (i.e. more or less cohesive sediment) for which light climate and changes in salinity are different, ii) their growth form (i.e. motile, immotile or amphibious) which determines their probability to be confronted to a combined high salinity-HL stress. Hence, the negative effect of high salinity on photosynthetic efficiency of benthic diatoms appears to be mostly restricted to epipsammon and tychoplankton, and in field conditions, its effect probably remains negligible compared to HL stress

Microphytobenthos primary production estimated by hyperspectral reflectance

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