Antifouling Marine Coatings with a Potentially Safer and Sustainable Synthetic Polyphenolic Derivative

Abstract

The development of harmless substances to replace biocide-based coatings used to prevent or manage marine biofouling and its unwanted consequences is urgent. The formation of biofilms on submerged marine surfaces is one of the first steps in the marine biofouling process, which facilitates the further settlement of macrofoulers. Anti-biofilm properties of a synthetic polyphenolic compound, with previously described anti-settlement activity against macrofoulers, were explored in this work. In solution this new compound was able to prevent biofilm formation and reduce a pre-formed biofilm produced by the marine bacterium, Pseudoalteromonas tunicata. Then, this compound was applied to a marine coating and the formation of P. tunicata biofilms was assessed under hydrodynamic conditions to mimic the marine environment. For this purpose, polyurethane (PU)-based coating formulations containing 1 and 2 wt.% of the compound were prepared based on a prior developed methodology. The most effective formulation in reducing the biofilm cell number, biovolume, and thickness was the PU-based coating containing an aziridine-based crosslinker and 2 wt.% of the compound. To assess the marine ecotoxicity impact of this compound, its potential to disrupt endocrine processes was evaluated through the modulation of two nuclear receptors (NRs), peroxisome proliferator-activated receptor γ (PPARγ), and pregnane X receptor (PXR). Transcriptional activation of the selected NRs upon exposure to the polyphenolic compound (10 µM) was not observed, thus highlighting the eco-friendliness towards the addressed NRs of this new dual-acting anti-macro- and anti-microfouling agent towards the addressed NRs.

Keywords: anti-biofilm; endocrine disruptor assessment; gallic acid; marine bacteria; safer chemicals.

Figure 1

Aims of this study and antifouling activity and (eco)toxicity previously described for GBA26 [12].

Figure 2

(A) Biofilm prevention and (B) biofilm reduction assays with different concentrations of GBA26. Different letters were given, when statistically significant differences existed at p < 0.05 (confidence level ≥ 95%). The average ± SDs for three independent assays are shown.

Figure 3

Effect of PU-based coatings containing different concentrations of GBA26 and a crosslinker (CL) on biofilm development in Pseudoalteromonas tunicata for 49 days. The analyzed parameter refers to biofilm cell numbers. Different letters were given, when statistically significant differences existed at p < 0.05 (confidence level ≥ 95%). The average ± SDs for three independent assays are shown.

Figure 4

Pseudoalteromonas tunicata biofilm architecture on a surface protected with 1 wt.% GBA26/PU coating, a surface treated with 2 wt.% GBA26/PU coating, and a surface treated with 2 wt.% GBA26/PU/CL coating after 49 days. These images were obtained from a confocal image series and are representative of the biofilm top view, with the virtual shadow projection on the right. The white scale bar corresponds to 50 µm.

Figure 5

(A) Biofilm biovolume and (B) thickness of the 49-days-old biofilms extracted from the confocal z-stacks with the COMSTAT tool. Different letters were given, when statistically significant differences existed at p < 0.05 (confidence level ≥ 95%). The average ± SDs for three independent assays are shown.

Figure 6

In vitro transcriptional activation of HsPPARγ, DrPPARγ, and DrPXR in the presence of 10 to 0.1 μM GBA26. Results are expressed as average fold induction relative to the vehicle control, DMSO, solid line (mean ± standard deviation). Asterisks denote significant differences (*** p < 0.001).