Valérie Stiger-Pouvreau

Effect of different conditioning treatments on total phenolic content and antioxidant activities in two Sargassacean species: Comparison of the frondose Sargassum muticum (Yendo) Fensholt and the cylindrical Bifurcaria bifurcata R. Ross

The effects of different conditioning treatments (fresh, freezing, freeze‐drying, oven‐drying and greenhouse‐drying) on the total phenolic content (TPC) and antioxidant activities of two brown algae, Sargassum muticum and Bifurcaria bifurcata, were investigated and compared. Phenolic compounds were extracted in a methanol/water (50:50) solution, and TPC was measured by the colorimetric Folin‐Ciocalteu assay. Antioxidant activity was assessed by the DPPH (2, 2‐diphenyl‐1‐picrylhydrazyl) radical scavenging assay and the β‐carotene bleaching method. The dried seaweeds showed lower phenolic contents and lower antioxidant capacities than the fresh and frozen ones, which suggests that the phenolic content and antioxidant activities are decreased by the drying treatments, especially, oven‐ and greenhouse‐drying. Relationships between TPC, antioxidant properties and conditioning treatments are discussed.

Anti-microfouling activities in extracts of two invasive algae: Grateloupia turuturu and Sargassum muticum

Marine macroalgae are particularly prone to epiphytism. The colonisation of their surface may lead to severe perturbations and sometimes to the death of the host. To protect themselves against settling and/or competing organisms, many algae have developed defences against fouling by producing a wide variety of chemically active metabolites. The goal of this study was to investigate potential anti-microfouling activities of two introduced algal species from the Brittany coast (France), Sargassum muticum (Phaeophyceae) and Grateloupia turuturu (Rhodophyceae). Thus, a complete study of the antimicrobial activities of extracts (aqueous, acetone, chloroform, dichloromethane, diethyl-ether, ethyl acetate, ethanol 96°, hexane and methanol) from S. muticum and G. turuturu against marine fouling bacteria (5 strains), fungi (5 strains) and biofilm-associated microphytobenthic strains (5) were performed. The most active extract of G. turuturu was the dichloromethane fraction, while the chloroform extract from S. muticum showed some good results. Our data suggest that these macroalgae can provide useful compounds or templates for industrial anti-microfouling applications.

TAXONOMIC REVISION OF SARGASSUM (FUCALES, PHAEOPHYCEAE) FROM FRENCH POLYNESIA BASED ON MORPHOLOGICAL AND MOLECULAR ANALYSES1

An assessment of Sargassum in French Polynesia was done through the critical revision of the literature, type specimens, and specimens from type localities. Sargassum samples were newly collected, and four morphotypes were identified on the basis of morphological characters. Molecular analysis of the nuclear ITS2, chloroplastic partial rbcLS, and mitochondrial cox3 markers generated two clades and confirmed the recent divergence suspected between closely related species. Although 18 different epithets have been attributed to French Polynesian Sargassum since 1828, only three species are considered valid in this study. Most of these species were transferred to S. pacificum Bory, the only species present in the Society Archipelago, while S. obtusifolium J. Agardh was restricted to the Austral Archipelago, and S. echinocarpum J. Agardh was confirmed for the Austral and Gambier Archipelagos. A morphological identification key is provided, along with descriptions and illustrations for each polymorphic species. Moreover, the study of several regional collections underlined similar and low specific diversity among Sargassum populations in the southeastern Pacific. As a result of this study, we propose that S. bacciferum J. Agardh var. latiuscula Grunow, S. bisserula f. pacifica Grunow, S. boraborense (Grunow) Setch., S. mangarevense (Grunow) Setch., S. sociale (Grunow) Setch., and S. tahitense Grunow be considered as heterotypic synonyms of S. pacificum. Sargassum skottsbergii Sjöstedt, S. hawaiiensis Doty et Newhouse, S. divaricatum var. chilensis Grunow, S. obtusifolium J. Agardh f. chamberlainii Grunow, and S. obtusifolium J. Agardh f. lendigeroides Grunow are further regarded as heterotypic synonyms of S. obtusifolium.

Total phenolic, size‐fractionated phenolics and fucoxanthin content of tropical Sargassaceae (Fucales, Phaeophyceae) from the South Pacific Ocean: Spatial and specific variability

This innovative study investigates 18 Turbinaria and Sargassum brown seaweed samples from three archipelagos of the South West Pacific Ocean. The phenolic content of crude and size‐fractionated extracts was determined by the Folin‐Ciocalteu method; fucoxanthin was measured using high performance liquid chromatography. Although the phenolic content proved to be low for the species of both genera tested, the levels in the species of Turbinaria were higher than those of Sargassum tested, except in the Fiji islands where both species produced similar contents. These investigations also highlighted variations of total phenolic content with spatial, reef morphology and depth. A large number of small phenolic compounds (<2000 Da) were observed irrespective of the genus analyzed. Nevertheless, the composition of the phenolic pool varied in relation with the genus, the archipelago from which the material was collected, geomorphological features and the depth of each collection field site. A similar observation was for fucoxanthin content and in general, the measured constituents of the Turbinaria were less than those of the Sargassum species. The results are discussed in terms of inter‐ and intra‐specific variability. Variations in both phenolic and fucoxanthin content were noted in tropical members of the Sargassaceae; such differences could be a result of specific chemical defense mechanisms adopted by members of each genus.

Phenology, TPC and size-fractioning phenolics variability in temperate Sargassaceae (Phaeophyceae, Fucales) from western Brittany: native versus introduced species.

The phenology of the introduced Sargassum muticum and two native species Bifurcaria bifurcata and Cystoseira baccata were monitored during eighteen months at two sites in Brittany. Density and length varied seasonally only in Sargassum. Larger individuals of Sargassum were observed in summer whereas in Cystoseira, they appeared almost in autumn. Peaks in maturity were delayed: in summer for Sargassum and in winter for Cystoseira and Bifurcaria. Phenolic contents increased before their respective reproductive period as a chemical defence. Moreover, size composition varied with site and season depending on species. In Sargassum, the quantity of small compounds decreased in summer together with an increase of 2000/5000 Da compounds. In Bifurcaria 2000/5000 Da compounds increased in summer (photoprotection) while in Cystoseira it increased in winter (protection for reproduction). Sargassum presented then a phenological plasticity not observed in native species. Moreover the three species possessed different chemical strategies to succeed in partitioning their vital space.

Structural elucidation, in vitro antioxidant and photoprotective capacities of a purified polyphenolic-enriched fraction from a saltmarsh plant

In temperate saltmarshes, halophytic plants have to daily protect their internal tissues against sunlight and UV rays. Consequently, they develop adaptive responses such as the synthesis of secondary metabolites, including polyphenols. The present study focused on the biological activities of fractions enriched in polyphenols from Salicornia ramosissima. Three different extracts were obtained by purification processes to concentrate polyphenols: a crude hydroalcoholic extract, and two purified fractions: an ethyl acetate fraction (EAF) and an aqueous fraction. Phenolic and flavonoid contents, antioxidant (DPPH radical-scavenging activity, reducing activity, β-carotene linoleic acid system and the ORAC method) and sunscreen properties (Sun Protection Factor and UVA-Protection Factor) were assessed by in vitro tests. The purification process was effective in increasing phenolic and flavonoid contents as well as antioxidant and sunscreen capacities of the EAF. The EAF appeared to be a broad spectrum UV absorber. The chemical structure of 10 EAF polyphenols was elucidated using 2D NMR and mass spectrometry spectra. Furthermore, a correlation was observed between phenolic composition and biological activity. These findings are encouraging for the future use of S. ramosissima as a potential source of antioxidant and photoprotectant molecules for industrial applications.

Sunscreen, antioxidant, and bactericide capacities of phlorotannins from the brown macroalga Halidrys siliquosa

The present study focused on a brown macroalga (Halidrys siliquosa), with a particular emphasis on polyphenols and their associated biological activities. Two fractions were obtained by liquid/liquid purification from a crude hydroethanolic extract: (i) an ethyl acetate fraction and (ii) an aqueous fraction. Total phenolic contents and antioxidant activities of extract and both fractions were assessed by in vitro tests (Folin–Ciocalteu test, 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity, reducing power assay, superoxide anion scavenging assay, and β-carotene–linoleic acid system). For the most active fraction, i.e., the ethyl acetate fraction, the oxygen radical absorbance capacity (ORAC) value, antibacterial activities, and sunscreen potential (Sun Protection Factor and UV-A-Protection Factor) were tested in vitro. A high correlation found between antioxidant activities and total phenolic content was interpreted as the involvement of polyphenolic compounds in antioxidant mechanisms. Interestingly, the ethyl acetate fraction appeared to be a broad-spectrum UV absorber and showed a strong bactericidal activity against Pseudomonas aeruginosa, Staphylococcus aureus, and Escherichia coli. In this fraction, four phenolic compounds (trifuhalols and tetrafuhalols and, for the first time, diphlorethols and triphlorethols) were identified using 1D and 2D nuclear magnetic resonance (NMR) and MS analysis. These findings are promising for the use of H. siliquosa, abundant in Brittany, as a valuable source of photoprotectant molecules for sunscreen and cosmetic applications.

Extraction and Purification of Phlorotannins from Brown Algae

The interest in the physiological roles and bioactivities of plant phenols has increased over the past decades. In seaweeds, many investigations have dealt with phenolic compounds of Phaeophyceae (phlorotannins), even though little is known so far about the ecophysiological variations of their pool or their biosynthetic pathways. We describe here a simple procedure based on the use of water-organic solvent mixtures for the extraction of phlorotannins. Crude extracts are semi-purified and fractionated by separating methods based on both the polarity and the molecular size of compounds. Phenols are then quantified by the Folin-Ciocalteu method and their radical-scavenging activity is characterized using the DPPH test. All along the purification process of phenolic compounds, the efficiency of separation is assessed by (1)H-NMR.

Spatiotemporal variations of diterpene production in the brown macroalga Bifurcaria bifurcata from the western coasts of Brittany (France)

Bifurcaria bifurcata, a temperate brown macroalga, is known to show spatial fluctuations in its diterpene content along the northwestern coasts of France (Brittany). In the aim to identify environmental factors which could influence the occurrence of a particular chemical type, several populations of B. bifurcata were collected in summer 2009 and winter 2010. Their chemical composition was studied through thin layer chromatography (TLC) and nuclear magnetic resonance (NMR) analyses. Results showed that specific diterpenes are biosynthesized depending on seasons and abiotic factors, such as hydrodynamism or substratum. Exposed sites were characterized by thalli of B. bifurcata producing two main diterpenoids, bifurcane, and eleganediol, whereas thalli from sheltered sites showed crude extracts containing a major diterpene, eleganolone. On these last sites, another diterpene (bifurcanone) is only expressed in winter and was thus considered as a seasonal chemomarker. The term “chemotype” applied to a population is proposed and discussed.

Isolation of turbinaric acid as a chemomarker of Turbinaria conoides (J. Agardh) Kützing from South Pacific Islands

Several species of the genus Turbinaria coexist along the coasts of islands in the Indian and Pacific Oceans. Among these brown algae, Turbinaria ornata and T. conoides are sister species that are difficult to differentiate using exclusively morphological characters. Based on in vivo nuclear magnetic resonance and chromatographic techniques, i.e., liquid and gas chromatography‐mass spectrometry analysis, combined with phylogenetic data, we successfully identified turbinaric acid in T. conoides samples from several Indian and Pacific Ocean islands. This nonvariable discriminant molecule was only identified in T. conoides specimens, but not in the two allied species T. ornata and T. decurrens. Results are discussed with regard to turbinaric acid as an interesting chemomarker isolated from T. conoides and the rapid discrimination of Turbinaria specimens using chemical assays.