Allelopathy Effect of the Blue Diatom HasleaOstrearia (Gaillon) Simonsen: Growth Inhibition in Aquaculture Relevant Microalgae

We are well known that the marine pennate diatom Hasleaostrearia (Gaillon) Simonsen produces the blue-green pigment called marennine. Marennine was identified as a polyphenolic compound. This compound is capable to inhibit the growth of herpes simplex virus type 1 (HSV-1) and several bacteria, including pathogens as Vibrio sp. The aim of this study was to determine how strong the allelophatic effect of marennine is generated byH. ostrearia and identifying its minimal concentration that inhibits the growth of other microalgae. The experiment consisted of two phases of research activities. The first phase was biovolumecomparaison between H. ostrearia and microalgae suitable for aquaculture tested to take into account the differences in size of the microalgae tested(Tetraselmissuecica, Chaetocerosgracilis, Skeletonemacostatum, PavlovalutheriandIsochrysisgalbana (T-Iso) in term of H. ostrearia biomass and production of marennine. The second phase was the bioactivity tests, which is include growth kinetics, allelophatic effects and concentration of marennine in the culture medium, measured with spectrophotometer. The results of this study showed that H. ostrearia could inhibit several species of microalgae currently used in aquaculture (T. suecica, C. gracilis and S. costatum). The statistical analysis (One way ANOVA) showed that there are significant differences (P < 0, 05) between treatments andwhen co-cultured with H. ostrearia, these microalgae exhibited a significant growth inhibition. The highest inhibition value was 97.77% (on the treatementH. ostrearia+C. gracilis). In this treatment, the concentration of marennine in the culture was 5.35 mg L-1. According to the results, we can conclude that the supernatant of H. ostrearia with marennine acts as an allelochemical. The minimal concentration is 0.23 mg L-1 and the highest is 5.35 mg L-1. The treatments H. ostreariawithP. lutheri and T-Iso did not performed any inhibition

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

Ion-driven communication and acclimation strategies in microalgae

Similar to all living organisms since their appearance on Earth, microalgae have continuously been exposed to natural selection and consequently evolved by adapting to different or changing ecological niches and occupying ecosystems worldwide, with concomitant genetic mutations. This has to be distinguished from acclimation, a response to environmental stressors which can occur over several generations without genetic changes, and for which phenotypic plasticity can be critical. Pertaining to both mechanisms, microalgae can sense, cooperate and propagate a timely warning message upon changes in the environment. This is key to maintain communities thriving and sustain primary production and mineralization in most ecosystems, but also for sustainability in large scale production of microalgae such as for biofuels production. Nevertheless, the nature of ubiquitous cell–cell interactions and communications, mostly prompted by stress-induced alterations, remains poorly understood, especially due to the lack of technologies suited to decipher cohort signalling and communication. Here, we have critically reviewed microalgae literature, unravelling important cues in microalgae populations that co-ordinate responses to changes in light, temperature, reproduction, grazers and osmotic stress, most likely through a mass diffusion process over a “handover distance”. We concluded that bioelectricity mediated through paracrine signalling, mostly involving Ca2+, plays a key role in microalgae cell sensing and communication, being the mediator for timely perception and concomitant collective stress acclimation. This critical analysis and the hypothesis proposed pave the way for quantitative electrogenic assessments of Ca2 + signalling and also of the acclimation potential and exquisite evolutionary perseverance of numerous microalgal lineages

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)

Duration of rapid light curves for determining the photosynthetic activity of microphytobenthos biofilm in situ

International audienceThis study is the first field work that examines the use of rapid light curves (RLCs) for in situ assessment of microphytobenthos (MPB) photosynthetic activity. The advantages offered by RLC methodology respond primarily to in situ constraints concerning MPB ecology and behaviour. In particular, the rapidity of RLCs allows for a high number of replicates during emersion, while preventing disturbance of the measurement due to MPB cell migration. It is necessary to maintain this feature in order to thoroughly assess the large spatial and temporal variability of in situ MPB biomass and photosynthetic activity. Consequently, working with intertidal mudflat MPB biofilms dominated by epipelic (motile) species, we investigated the effect of 10-s and 30-s irradiance steps: two durations commonly used for building RLCs. We compared the performance of 10-s and 30-s RLCs in determining the in situ MPB photosynthetic activity without dark acclimation and in high irradiances (summer). Although a similar trend of MPB cell photoacclimation was observed using the two procedures, there were differences, revealed by lower values of α -10 s and rETRmax-30 s compared with α -30 s and rETRmax-10 s on some experimental days (49% and 34%, respectively). Discrepancies could mainly be explained by the unbalanced QA redox state and the occurrence of photoprotective non-photochemical quenching (NPQ) present prior to RLC, which impacted the 10-s and 30-s RLCs differently. The initial slope (α ) was strongly impacted by NPQ developed prior to RLCs. A correction performed a posteriori and based on the use of the maximum Fm′Fm′ obtained during the course of RLCs was not sufficient to remove the bias of pre-existing NPQ on the determination of α completely. Consequently, a good, direct and simultaneous determination of rETRmax and α was virtually impossible in situ even when using RLCs. In contrast to published results from laboratory studies, the shorter irradiance steps (10 s) offers the better (i.e. the most reasonable) compromise for assessing MPB maximum photosynthetic capacity in situ using RLC

Detection of diatom xanthophyll cycle using spectral reflectance

Analysis of reflectance spectra was used to monitor the conversion of diadinoxanthin (DD) into diatoxanthin (DT) in two benthic diatom species, Amphora coffeaeformis (C. Agardh) Kütz. and Cylindrotheca closterium (Ehrenb.) J. C. Lewin et Reiman, cultured at high light (HL, 400 μmol · m−2 · s−1 PAR) and low light (LL, 25 μmol · m−2 · s−1 PAR). Cultures were exposed to saturating light for 32 min. HL cultures of both species showed higher (DT + DD) content, whereas LL cultures exhibited higher chl a and fucoxanthin content. DD to DT conversion, measured by HPLC, occurred mainly in the first 2 min (LL) or 5 min (HL) after exposure to saturating light. Nonphotochemical quenching (NPQ), measured by PAM fluorescence, showed the same pattern as DT/(DD + DT), resulting in a linear relationship between these parameters. Addition of dithiothreitol (DTT) blocked the conversion of DD into DT and significantly reduced NPQ induction. Reflectance spectra showed no obvious change after light exposure. However, second derivative spectra (δδ) showed a shift in reflectance from 487 to 508 nm, which was not present for DTT-treated samples. Changes in δδ487 were strongly correlated with changes in DD (r = 0.76), while changes in δδ508 were strongly correlated with changes in DT (r = 0.94). The best index to estimate DD to DT conversion was δδ508/δδ630 (r = 0.87). This index was very sensitive to minute changes that occurred immediately after exposure to light and was species insensitive. Good relationships were observed between indices for xanthophyll cycle activation (DD to DT conversion and NPQ induction) and the second derivative spectra. With further in situ validation, this index may prove to be highly useful for investigation into aquatic global photoregulation mechanisms in diatom-dominated samples

Comparative efficiency of macroalgal extracts and booster biocides as antifouling agents to control growth of three diatom species.

International audienceThe application of 'booster biocides' Diuron, Tolylfluanid and Copper thiocyanate inbantifouling paints, used to prevent development of biofouling, needs to be monitored before assessing their impacts on the environment. An alternative approach aims to propose eco-friendly and effective antifoulants isolated from marine organisms such as seaweeds. In this study, the effects of 'booster biocides' and the ethanol and dichloromethane extracts from a brown (Sargassum muticum) and a red alga (Ceramium botryocarpum) have been compared by algal growth inhibition tests of marine diatoms. The most efficient extracts were ethanol fraction of S. muticum and C. botryocarpum extracts with growth EC(50)=4.74 and 5.3μg mL(-1) respectively, with reversible diatom growth effect. The booster biocides are more efficient EC(50)=0.52μg mL(-1), but are highly toxic. Results validate the use of macroalgal extracts as non toxic antifouling compounds, and they represent valuable environmentally friendly alternatives in comparison with currently used biocides

Migration or photoacclimation to prevent high irradiance and UV-B damage in marine microphytobenthic communities

Microphytobenthos (MPB) on intertidal mudflats is a major component of primary producers in some estuarine ecosystems. To sustain photosynthesis, MPB migrate through the upper sediment layer and form transient biofilms during emersion periods, and thus may be exposed to high irradiance and ultraviolet radiation (UV-R), possibly resulting in photodamage to the photosynthetic apparatus. In contrast, downard migration could allow cells to optimize position in the photic zone, avoiding photoinhibitory light levels. Engineered biofilms with inhibited migratory capacity were used to distinguish between possible strategies (photoacclimation or migration) evolved by MPB to cope with photoinhibitory irradiances, when a series of UV filters with different cut-off wavelengths was used to estimate the respective contribution of visible light and UV-R. Engineered biofilms with full migratory capacity maintained a high relative electron transport rate (rETR), in contrast to engineered non-migratory biofilms, which showed a decrease in rETR under high irradiance, with a greater decrease under UV-B radiation. Migration thus appeared to be the principal short-term mechanism allowing MPB to avoid or minimize UV-R and high PAR photodamage in situ. Nevertheless, physiological acclimation processes to different light levels (‘light-shade’ patterns) seem to occur in the long term, and probably superimpose on migratory capacity, making light history an important component of MPB photoacclimation strategies

Prophylactic effect of Haslea ostrearia culture supernatant containing the pigment marennine to stabilize bivalve hatchery production

International audience– This paper explores the possibility of using the supernatant of Haslea ostrearia culture containing maren-nine, a natural microalgal pigment, as an antimicrobial in bivalve hatcheries. The blue mussel Mytilus edulis and the scallop Placopecten magellanicus were used as model animals, and the pathogenic marine bacteria Vibrio splendidus was used to induce larval mortality. The hypothesis tested was that V. splendidus pathogenicity in larval rearings can be controlled by using marennine-containing culture supernatants. The effect of three marennine concentrations was tested on a larval rearing over 20 days for M. edulis and 9 days for P. magellanicus. At a low dose (0.1 mg L −1), survival and physiological condition were both higher than in the control. In bacterial challenges, larvae were exposed to V. splendidus for 72 h, with or without marennine. The bacterial challenge caused significant mortality when compared to controls, while the marennine-treated larvae showed significantly higher survival. Results show that marennine is an interesting molecule for pathogen control in hatcheries as it is active at low concentrations and significantly enhanced larval survival and physiological condition