Settlement inhibition of marine biofilm bacteria and barnacle larvae by compounds isolated from the Mediterranean brown alga Taonia atomaria
Résumé
The antifouling (AF) properties of phytochemicals isolated from the Mediterranean brown seaweed Taonia atomaria have been assayed against several colonizing organisms. Eight compounds were isolated and their chemical structures characterized by spectroscopic techniques (NMR, MS) and comparison with literature data. The phytochemical composition of the extracts of T. atomaria was found to be mainly attributable to sesquiterpenes. Accordingly, a new germacrane, germacra-4(15),5,10(14)-trien-9-ol (1), is described together with five other sesquiterpenoids (-)-gleenol (2); α-cadinol methyl ether (3), (-)-trans-calamenene (4), (1S, 5E, 7S) 1-acetoxygermacra-4(15),5,10(14)-triene (5), and 4-peroxymuurol-5-ene (6). Moreover, two lipidic compounds, a polyunsaturated fatty acid, (5Z, 8Z, 11Z, 14Z, 17Z)-eicosa-5,8,11,14,17-pentaenoic acid (7), and a glycerol derivative, sn-3-O-(geranylgeranyl)glycerol (8), were also isolated. The known compounds 3, 6–7 are described here for the first time from this alga. In comparison with commercial antifoulants [tributyltin oxide (TBTO), zineb, and copper pyrithione (CuPT)], compounds 1, 2, 4, 6, and 8 were evaluated for their toxicity and capacity to inhibit the settlement of five bacteria isolated from marine biofilms. Toxicity and anti-settlement activity of 1, 2, and 6 were also assessed against two barnacle species (Amphibalanus amphitrite and Balanus perforatus). Regarding bacteria, a significant anti-adhesion effect was recorded for 8 (EC50 between 25 and 50 μM) with moderate associated toxicity. Considering the settlement inhibition of barnacle cyprids, (-)-gleenol (2) exhibited a strong AF efficacy (EC50 < 5 μM) with moderate toxicity. In addition, as B. perforatus showed similar responses to the reference A. amphitrite with all compounds, this species may be proposed as an alternative model for anti-macrofouling assessment, especially in temperate areas. Overall, these results suggest that a number of the tested compounds could, alone or in combination, play a critical role in limiting the fouling at the T. atomaria surface.