Camille Jégou

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.

Antimicrobial Peptides from Marine Proteobacteria

After years of inadequate use and the emergence of multidrug resistant (MDR) strains, the efficiency of “classical” antibiotics has decreased significantly. New drugs to fight MDR strains are urgently needed. Bacteria hold much promise as a source of unusual bioactive metabolites. However, the potential of marine bacteria, except for Actinomycetes and Cyanobacteria, has been largely underexplored. In the past two decades, the structures of several antimicrobial compounds have been elucidated in marine Proteobacteria. Of these compounds, polyketides (PKs), synthesised by condensation of malonyl-coenzyme A and/or acetyl-coenzyme A, and non-ribosomal peptides (NRPs), obtained through the linkage of (unusual) amino acids, have recently generated particular interest. NRPs are good examples of naturally modified peptides. Here, we review and compile the data on the antimicrobial peptides isolated from marine Proteobacteria, especially NRPs.

Spotlight on Antimicrobial Metabolites from the Marine Bacteria Pseudoalteromonas: Chemodiversity and Ecological Significance.

This review is dedicated to the antimicrobial metabolite-producing Pseudoalteromonas strains. The genus Pseudoalteromonas hosts 41 species, among which 16 are antimicrobial metabolite producers. To date, a total of 69 antimicrobial compounds belonging to 18 different families have been documented. They are classified into alkaloids, polyketides, and peptides. Finally as Pseudoalteromonas strains are frequently associated with macroorganisms, we can discuss the ecological significance of antimicrobial Pseudoalteromonas as part of the resident microbiota.

Phlorotannins in sargassaceae species from brittany (France): Interesting molecules for ecophysiological and valorisation purposes

Phlorotannins are metabolites synthesised by brown algae to protect against environmental stresses. Only a few studies presented structural elucidation of native molecules extracted from macroalgae, contrary to previous published studies, which characterised acetylated phlorotannins. The present work introduces quantitative and qualitative studies to characterise phlorotannins from the eight species of Sargassaceae settled in Brittany, using a colorimetric method used for quantification of total phenolic content (TPC), and one- and two-dimensional nuclear magnetic resonance (NMR) (1H, heteronuclear multiple bond correlation) together with in vivo NMR (high-resolution magic-angle spinning (HR-MAS) NMR) analyses, with the aim to elucidate structural and fingerprint of phlorotannins signals. Halidrys siliquosa, which settles in low tide rock pools, exhibited high TPC (17.77±1.68% dry weight (DW)) while the other species showed lower TPC (ranged from 0.85±0.11% DW for Cystoseira baccata growing in low tide rock pools to 5.53±0.63% DW in Cystoseira humilis growing in high tide rock pools). No relation between TPC and the position of the algae along the shore could be highlighted. Fingerprints using NMR HR-MAS were useful to compare the eight species in terms of phenolic content and in terms of phenolic signals as the species from Brittany produced different phlorotannins. Our study demonstrated that Cystoseira tamariscifolia produced the monomer (phloroglucinol), C. humilis, phloroglucinol and a phlorethol, C. baccata and Cystoseira nodicaulis produced many compounds, i.e. traces of phloroglucinol together with fucols, phlorethols, and fucophlorethols and finally fuhalols were identified in Bifurcaria bifurcata and H. siliquosa. The putative ecophysiological roles of these phlorotannins from Sargassaceae are discussed, together with their potential bioactivities.

Deep Subseafloor Fungi as an Untapped Reservoir of Amphipathic Antimicrobial Compounds

The evolving global threat of antimicrobial resistance requires a deep renewal of the antibiotic arsenal including the isolation and characterization of new drugs. Underexplored marine ecosystems may represent an untapped reservoir of novel bioactive molecules. Deep-sea fungi isolated from a record-depth sediment core of almost 2000 m below the seafloor were investigated for antimicrobial activities. This antimicrobial screening, using 16 microbial targets, revealed 33% of filamentous fungi synthesizing bioactive compounds with activities against pathogenic bacteria and fungi. Interestingly, occurrence of antimicrobial producing isolates was well correlated with the complexity of the habitat (in term of microbial richness), as higher antimicrobial activities were obtained at specific layers of the sediment core. It clearly highlights complex deep-sea habitats as chemical battlefields where synthesis of numerous bioactive compounds appears critical for microbial competition. The six most promising deep subseafloor fungal isolates were selected for the production and extraction of bioactive compounds. Depending on the fungal isolates, antimicrobial compounds were only biosynthesized in semi-liquid or solid-state conditions as no antimicrobial activities were ever detected using liquid fermentation. An exception was made for one fungal isolate, and the extraction procedure designed to extract amphipathic compounds was successful and highlighted the amphiphilic profile of the bioactive metabolites.

NMR use to quantify phlorotannins: The case of Cystoseira tamariscifolia, a phloroglucinol-producing brown macroalga in Brittany (France)

Among the most renowned natural products from brown algae, phlorotannins are phloroglucinol polymers that have been extensively studied, both for their biotechnological potential and their interest in chemical ecology. The accurate quantification of these compounds is a key point to understand their role as mediators of chemical defense. In recent years, the Folin-Ciocalteu assay has remained a classic protocol for phlorotannin quantification, even though it frequently leads to over-estimations. Furthermore, the quantification of the whole pool of phlorotannins may not be relevant in ecological surveys. In this study, we propose a rapid (1)H qNMR method for the quantification of phlorotannins. We identified phloroglucinol as the main phenolic compound produced by the brown macroalga Cystoseira tamariscifolia. This monomer was detected in vivo using (1)H HR-MAS spectroscopy. We quantified this molecule through (1)H qNMR experiments using TSP as internal standard. The results are discussed by comparison with a standard Folin-Ciocalteu assay performed on purified extracts. The accuracy and simplicity of qNMR makes this method a good candidate as a standard phlorotannin assay.

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.

Bioactive Metabolites from the Deep Subseafloor Fungus Oidiodendron griseum UBOCC-A-114129

Four bioactive compounds have been isolated from the fungus Oidiodendron griseum UBOCC-A-114129 cultivated from deep subsurface sediment. They were structurally characterized using a combination of LC–MS/MS and NMR analyses as fuscin and its derivatives (dihydrofuscin, dihydrosecofuscin, and secofuscin) and identified as polyketides. Albeit those compounds were already obtained from terrestrial fungi, this is the first report of their production by an Oidiodendron species and by the deepest subseafloor isolate ever studied for biological activities. We report a weak antibacterial activity of dihydrosecofuscin and secofuscin mainly directed against Gram-positive bacteria (Minimum Inhibitory Concentration (MIC) equal to Minimum Bactericidal Concentration (MBC), in the range of 100 μg/mL). The activity on various protein kinases was also analyzed and revealed a significant inhibition of CDC2-like kinase-1 (CLK1) by dihysecofuscin.