Community analysis of pigment patterns from 37 microalgae strains reveals new carotenoids and porphyrins characteristic of distinct strains and taxonomic groups.

Phytoplankton, with an estimated 30 000 to 1 000 000 species clustered in 12 phyla, presents a high taxonomic and ecophysiological diversity, reflected by the complex distribution of pigments among the different algal classes. High performance liquid chromatography is the gold standard method for qualitative and quantitative analysis of phytoplankton pigments in seawater and culture samples, but only a few pigments can be used as robust chemotaxonomic markers. A major challenge is thus to identify new ones, characteristic of a strain, species, class or taxon that cannot be currently identified on the basis of its pigment signature. Using an optimized extraction process coupled to a HPLC de-replication strategy, we examined the pigment composition of 37 microalgae strains, representative of the broad taxonomic diversity of marine and freshwater species (excluding cyanobacteria). For each species, the major pigments already described were unambiguously identified. We also observed the presence of several minor unidentified pigments in each chromatogram. The global analysis of pigment compositions revealed a total of 124 pigments, including 98 pigments or derivatives unidentified using the standards. Absorption spectra indicated that 35 corresponded to chlorophyll/porphyrin derivatives, 57 to carotenoids and six to derivatives having both spectral signatures. Sixty-one of these unidentified or new carotenoids and porphyrin derivatives were characteristic of particular strains or species, indicating their possible use as highly specific chemotaxonomic markers capable of identifying one strain out of the 37 selected. We developed a graphical analysis using Gephi software to give a clear representation of pigment communities among the various phytoplankton strains, and to reveal strain-characteristic and shared pigments. This made it possible to reconstruct the taxonomic evolution of microalgae classes, on the basis of the conservation, loss, and/or appearance of pigments.

[Screening marine resources to find novel chemical inhibitors of disease-relevant protein kinases]. / Le criblage à Roscoff - Une recherche d'inhibiteurs de kinases tournée vers la mer.

Since the early 1970's, investigators at Station Biologique de Roscoff (SBR), France, have been using marine organisms as models to describe molecular pathways conserved through evolution in mammalian cells (e.g. the cyclin-dependent kinases involved in the control of the cell division cycle). Some kinases are misregulated in various human pathologies, including cancers. Using a specialized screening approach, chemical libraries were analysed, using on-site facilities at Roscoff, in order to identify small chemical inhibitors of protein kinases. Eight chemical scaffolds produced by marine organisms were characterized as candidate drugs by our screening facility, some of which are being considered as chemical tools to pinpoint specific cellular functions of the targeted kinases. In this review, we describe our existing screening facilities and we discuss new perspectives related to marine bioprospecting.

Selection and optimisation of a method for efficient metabolites extraction from microalgae.

Over the last decade, the use of microalgae for biofuel production and carbon dioxide sequestration has become a challenge worldwide. Processing costs are still too high for these methods to be profitable though, leading to a need to find high value by-products to optimise the added value of this biomass. For high-throughput screening of such metabolites, it is essential to reach the inner content of the cell. This paper presents research and development of a technique enabling a high extraction yield of any metabolite, taking into account the difficulty of extracting bound and or inaccessible molecules with a wide variety of polarities. To this end, several disruption techniques were tested at laboratory scale on two biological models: Porphyridium purpureum and Phaeodactylum tricornutum. A mixer mill gave the best results, offering access to a broad diversity of metabolites from microalgae for high-throughput screening.

Antiproliferative activity of violaxanthin isolated from bioguided fractionation of Dunaliella tertiolecta extracts.

Dunaliella tertiolecta (DT) was chemically investigated to isolate molecules inhibiting cancer cell proliferation and inducing apoptosis in vitro. The potency to inhibit cell growth was used for the bio-guided fractionation and isolation of active compounds using chromatographic techniques. The DT dichloromethane extract exhibited a strong anti-proliferative activity on MCF-7 and LNCaP cells, and was further fractionated and sub-fractionated by RP-HPLC. High resolution mass spectrometry and spectrophotometric analysis unequivocally identified violaxanthin as the most antiproliferative molecule present in DT DCM extract. Violaxanthin purified from DT induced MCF-7 dose-dependent growth inhibition in continuous and discontinuous treatments, at concentrations as low as 0.1 µg·mL⁻¹ (0.17 µM). Phosphatidylserine exposure, typical of early apoptosis, was observed after 48 h treatment at 8 µg·mL⁻¹ (13.3 µM) but no DNA fragmentation, characteristic of late apoptosis steps, could be detected even after 72 h treatment at 40 µg·mL⁻¹ (66.7 µM). Taken together, our results demonstrate the strong antiproliferative activity of violaxanthin on one human mammary cancer cell line, and suggest that studying the pharmacology of violaxanthin and pharmacomodulated derivatives on cancer cells may allow potent antiproliferative drugs to be obtained.