Antibiofouling activity of 1-hexadecyl-3-methylimidazolium chloride against Amphora sp. BARC 104, a fouling diatom isolated from back waters of Kalpakkam

Abstract

1-Hexadecyl-3-methylimidazolium chloride (C16MimCl), an alkylimidazolium ionic liquid (IL) with a long alkyl side chain (-hexadecyl group) is attractive for antimicrobial applications. However, there are limited studies on the antifouling efficacy of ILs using biofouling organisms especially diatoms. In this study, the antifouling activity of C16MimCl was determined against Amphora sp. BARC 104, a dominant fouling diatom isolated from Kalpakkam coastal waters. Growth of the diatom was inhibited in the presence of IL at varied concentrations starting from 0.15 μM C16MimCl. A complete inhibition in the growth was observed in the presence of 2.5 μM C16MimCl. Adhesion and biofilm formation by Amphora sp. was strongly inhibited at sub-micromolar concentrations of IL. Exposure of diatom cells to IL in acute toxicity assays induced oxidative stress (increased reactive oxygen species generation) and reduced metabolic activity (decreased esterase activity) as revealed by 2,7 -Dichlorodihydrofluorescein diacetate (DCH2FDA) and fluorescein diacetate (FDA) staining, respectively. SYTOX® Green staining and extracellular chlorophyll a measurement revealed a severe membrane damage and leakage of chlorophyll a, respectively, in IL treated diatom cells. These measurements during recovery experiments indicated a permanent damage to cell and thylakoid membranes in the diatom cells. Damage to multiple cellular targets coupled with strong antibiofilm activity suggest potential application of C16MimCl in preparation of antifouling formulations and coatings.