Nesrine Karkouch

Exopolysaccharide (EPS) from marine microalgae are promising sources of a new generation of drugs. However, lot of them remain to be discovered and tested. In this study, EPS produced by Porphyridium marinum and its oligomers prepared by High Pressure Homogenizer have been tested for different biological activities, i.e., antibacterial, anti-fungal and antibiofilm activities on Candida albicans, as well as for their effects on the viability of murine breast cancer cells. Results have shown that all EPS samples present some biological activity. For antibacterial and antibiofilm activities, the native EPS exhibited a better efficiency with Minimum Inhibitory Concentration (MIC) from 62.5 µg/mL to 1000 µg/mL depending on the bacterial strain. For Candida albicans, the biofilm formation was reduced by about 90% by using only a 31.3 µg/mL concentration. Concerning breast cancer cells, lower molar masses fractions appeared to be more efficient, with a reduction of viability of up to 55%. ...

La presente etude s’attache a etudier l’effet d’une source de carbone organique selectionnee sur la croissance et la production de metabolites de la microalgue rouge Porphyridium marinum. Cette derniere s’est montree incapable de se multiplier en heterotrophie, en absence totale de lumiere. Cependant, en condition mixotrophique la production de biomasse, lipides et de phycobiliproteines par P. marinum a ete amelioree en comparaison avec la condition autotrophique. Les teneurs en exopolysaccharides ont ete presque similaires dans les deux conditions. Dans le but de valoriser ces metabolites, l’effet antioxydant, antibacterien, antibiofilm et anticancereux ont ete testes. L’exopolysaccharide de P. marinum ainsi que ses derives de faible poids moleculaire (EPS-2P et EPS-5P) ont tous presente des activites antibacteriennes et antibiofilm a differentes concentrations. Cependant l’EPS-2P et l’EPS-5P ont ete juges plus efficaces pour l’activite anticancereuse contre les cellules de cancer ...

Optimal conditions for maximal biomass and starch production by the marine red microalgae Porphyridium marinum were investigated. Box-Behnken Design was used to model the effect of light intensity, NaNO3 concentration and salinity on the growth of microalgae but also on their starch and protein contents. These three factors increased biomass production by 13.6% in optimized conditions. A maximum starch production (140.21 μg·mL-1), 30.6% higher than that of the control, was attained at a light intensity of 100 μmol photons·m-2·s-1, a NaNO3 concentration of 1 g·L-1 and a NaCl concentration of 20 g·L-1. FT-IR spectroscopy was used to estimate the biochemical composition (carbohydrate accumulation) of P. marinum and revealed significant changes (P < 0.05) depending on culture conditions. FT-IR analysis highlighted also that the culture conditions leading to highest starch production by P. marinum corresponded to lowest sulfated polysaccharide and protein contents.

The production of B-phycoerythrin (B-PE) from the red microalga Porphyridium marinum was optimized before to purify it and subsequently study its antioxidant activities. NaNO3, K2HPO4 and metal traces concentrations of the culture medium, and luminosity parameters were chosen, according to the Plackett-Burman design, as the most influent factors on the B-PE production by P. marinum. The optimization of these factors according to the Box-Behnken plan gave a maximum of B-PE production equal to 40 mg/g dry weight under the following conditions: NaNO3 = 3.4 g/L; K2HPO4 = 0 g/L; light intensity = 70 μmol photons/m2/s and metal solution = 1.5 mL/L. The B-PE also showed an interesting capacity to chelate Fe3+ (IC50 = 13.91 ± 0.21 μg/mL) and a significant reducing power (OD700nm = 0.485 ± 0.011 at 100 μg/mL). The present study reports the antioxidant potential of purified B-PE from P. marinum that could be potentially used as a source of bioactive protein for a wide range of cosmetic and pharmaceutical applications.

The blue-green microalga, Arthrospira sp., isolated from the sea of Kssour Essef in Mahdia (Tunisia), was purified and then identified both morphologically and genetically based on 16S rRNA gene sequence. Following physicochemical analysis, the prokaryotic microalga tested represented a competitive source of pigments and showed a considerable rate in protein (64%) which was confirmed by FTIR measurement. The lipid content (4%) was quantified by the gravimetric method and the intracellular lipid bodies were detected with the Nile red staining. Using gas chromatography coupled with flame ionization detector, the fatty acid profile revealed the presence of 27.4% and 32.88% of monounsaturated fatty acids (MUFAs) and polyunsaturated fatty acids (PUFAs), respectively. Given the richness of the isolated microalga in unsaturated fatty acids, we have developed a SYBR Green real time PCR method for the specific identification of Arthrospira sp. Δ9 desaturase gene. This current method will be of great value for carrying out high-throughput studies like cloning, heterologous expression and structure-function relationship analysis.