Pelagic and biofilm marine bacteria. Initial screening of halophytic plant aqueous extracts: effective inhibition of marine micro and macrofouling

In this study, we screened for the antifouling activity of five species plant aqueous extracts against marine micro and macrofouling, and also assessedtheir potential toxicity effects . Thirteen aqueous extracts of halophytic plants were tested at different concentration levels (0, 0.5, 1, 2, 4, and 8 mg mL-1). For microfouling inhibition assay, a natural marine bacterial consortium was inoculated in multi-well plates and incubated under the different treatments for 48 h. The biofilm bacteria inhibition potential was evaluated through flow cytometry (density) and by crystal violet (biomass) assays. The macrofouling settlement inhibition was evaluated using Amphibalanus amphitrite cyprids as a settling model organism. The toxicological effects of the treatments were evaluated by marine planktonic bacteria consortium biomass, barnacle cyprid survival (LC50), barnacle nauplii II survival (LC50) and both mortality and immobility (EC50). Twenty eight extracts showed antibiofilm activity by inhibiting bacteria density (≥ 80%) and biomass (≥22%) in at least one concentration, without killing planktonic bacteria . Regarding to macrofouling, twenty-nine extracts showed A. amphitrite settlement inhibition (≥11%) in at least one concentration, without causing toxicity to barnacle larvae (nauplii II and cyprid). The antifouling activity profile of the present investigation suggested that extracts at 4.0 mg mL-1 of Apium graveolens branches, 1.0 and 2.0 mg mL-1 of A. graveolens leaves, 8.0 mg mL-1 of Myrsine parvifolia seeds, 4.0 mg mL-1 of M. parvifolia branches, 0.5 and 1.0 mg mL-1 of Vigna luteola seeds, 0.5 mg mL-1 of Salicornia neei mix 1 and 1.0 and 2.0 mg mL-1 of S. neei mix 2 have potent non-toxic antifouling activity which can be used for the development of eco-friendly antifouling products. Our work demonstrates the biotechnological potential of halophytic plant extracts as potential substitutes to highly toxic traditional antifouling paints and opens on the prospect for more sustainable alternatives in biofouling research.