Bioactivity of amphidinol-like extracts of Amphidinium carterae grown under varying cultivation conditions

Abstract Microalgae have attracted interests from the bioenergy, bioremediation, cosmetics and pharmaceutical sectors due to produce biofuels, pigments, omega-3 fatty acids, antioxidants or antimicrobial compounds. Among others, amphidinol-like compounds biosynthesised by dinoflagellate species of the genus Amphidinium have shown promising antimicrobial properties. Here, a two-stage cultivation regime was used to grow A.carterae (subclade III), which was exposed to different conditions, including an illumination regime switch to LED blue light, a salinity enhancement treatment, sodium carbonate or hydrogen peroxide supplementation. A solid phase extraction of the dried biomass was carried out and returned 6 fractions for each treatment, which were analysed by LC-HRMS. Amphidinol-like compounds AM-B, AM-C, AM-22 and AM-A were detected through their fragmentation patterns, mostly in Fraction-4 samples. AM-B was the major analogue in Fraction-4 ( m/z 1463.69, 42.3 + / - 16.5 % of amphidinol composition), followed by AM-C ( m/z 1343.84, 21.4 + / - 6.6 %). In Fraction-5, along with an unidentified analog with m/z AM-1320, AM-C was the most prevalent amphidinol (15.5 + / - 3.0 %) which was on average as abundant as in Fraction-4. This returned the highest antimicrobial activity against the pathogens S.aureus , E.faecalis and C.albicans , with MBC ranging from 1 to 512 µg×mL -1 . Further analysis using the Bocillin competition assay showed that the antibacterial activity was not associated with the presence of compounds targeting penicillin binding proteins (PBPs) in the cell wall of bacteria. Results indicate that the modulation of both amphidinol profile and fraction bioactivity can be induced by adjusting the cultivation parameters used to grow two-stage batch cultures of A. carterae .