Exploring the chemodiversity of tropical microalgae for the discovery of natural antifouling compounds
Marine microalgae and cyanobacteria have largely been studied for their biotechnological potential and proved their ability to produce a wide array of bioactive molecules. We investigated the antifouling potential of unexplored benthic tropical microalgae using anti-adhesion and toxicity bioassays against two major micro- and ma crobiofoulers, namely bacteria and barnacles. Fifty strains belonging to six phyla [Cyanobacteria, Miozoa (Dinoflagellata), Bacillariophyta, Cryptophyta, Rhodophyta and Haptophyta] were isolated from southwestern Islands of the Indian Ocean. They were chosen in order to represent as much as possible the huge biodiversity of such a rich tropical ecosystem. The associated chemodiversity was highlighted by both NMR- and LC-MS-based metabolomics. The screening of 84 algal fractions revealed that the anti-adhesion activity was concentrated in methanolic ones (i.e. 93% of all active fractions). Our results confirmed that microalgae constitute a promising source of natural antimicrofoulants as 17 out of the 30 active fractions showed high or very high capacity to inhibit the adhesion of three biofilm-forming marine bacteria. Dinoflagellate-derived fractions were the most active, both in terms of number and intensity. However, dinoflagellates were also more toxic and may not be suitable as a source of environmentally friendly antifouling compounds, in contrast to diatoms, e.g. Navicula mollis. The latter and two dinoflagellates of the genus Amphidinium also had interesting anti-settlement activities while being moderately toxic to barnacle larvae. Our approach, combining the bioprospecting of a large number of tropical microalgae for their anti-settlement potential and metabolomics analyses, constituted a first step towards the discovery of alternative ecofriendly antifoulants.
KeywordsMicroalgae Antifouling Bioassay Chemodiversity Bioprospecting Metabolomics
The authors would particularly like to thank Dr. Nicolas Chomérat (Ifremer, France), Maurice Loir and Dr. Mitsunori Iwataki (University of Tokyo, Japan), for their help in Amphidinium, Prorocentrum and Navicula species identification. They also would like to thank Qiong-Yao Xue, Emmanuelle Espuche and Lucie Bruno for the technical assistance (extraction of microalgae and some bioassays).
This study was funded by the French National Research Agency (project BioPainTrop, ANR-12-CDII-0008).
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