Abstract
Microalgae have received growing interest for their capacity to produce bioactive metabolites. This study aimed at characterising the antimicrobial potential of the marine dinoflagellate Amphidinium carterae strain LACW11, isolated from the west of Ireland. Amphidinolides have been identified as cytotoxic polyoxygenated polyketides produced by several Amphidinium species. Phylogenetic inference assigned our strain to Amphidinium carterae subclade III, along with isolates interspersed in different geographic regions. A two-stage extraction and fractionation process of the biomass was carried out. Extracts obtained after stage-1 were tested for bioactivity against bacterial ATCC strains of Staphylococcus aureus, Enterococcus faecalis, Escherichia coli and Pseudomonas aeruginosa. The stage-2 solid phase extraction provided 16 fractions, which were tested against S. aureus and E. faecalis. Fractions I, J and K yielded minimum inhibitory concentrations between 16 μg/mL and 256 μg/mL for both Gram-positive. A targeted metabolomic approach using UHPLC-HRMS/MS analysis applied on fractions G to J evidenced the presence of amphidinol type compounds AM-A, AM-B, AM-22 and a new derivative dehydroAM-A, with characteristic masses of m/z 1361, 1463, 1667 and 1343, respectively. Combining the results of the biological assays with the targeted metabolomic approach, we could conclude that AM-A and the new derivative dehydroAM-A are responsible for the detected antimicrobial bioactivity.
Highlights
Several bioactive metabolites isolated from marine bioresources, known as marine natural products (MNPs), have elicited potent bioactivity against cancer and other ailments induced by pathogens such as viruses, bacteria and fungi [5,6,7]
The four subgroups of Amphidinium carterae characterised in previous studies were visible; the Irish strain LACW11 clustering with other isolates from
The culture of A. carterae LACW11 was maintained for 30 days in f/2 medium and harvested during the exponential phase (Figure 2)
Summary
The emergence of antimicrobial resistance has hindered the effectiveness of treatments for a growing number of bacterial infections worldwide [1,2]. The overuse and misuse of antibiotic drugs have led bacteria to develop adaptations to overcome the mechanisms of action of several commonly used drugs [3,4], requiring the urgent identification of novel antimicrobial compounds. Several bioactive metabolites isolated from marine bioresources, known as marine natural products (MNPs), have elicited potent bioactivity against cancer and other ailments induced by pathogens such as viruses, bacteria and fungi [5,6,7]. Antimicrobial MNPs show a high chemical diversity and include, for example, alkaloids, terpenoids, peptides, halogenated compounds, polyketides, isocoumarins, or nucleosides [6,8]
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