Fig 1.
Schematic representation of the biofouling process.
Fig 2.
Structures and cLogP values of the compounds used in this study.
Table 1.
Activity displayed by the tested compounds towards different fouling organisms.
Fig 3.
Correlation between the activity and the cLogP of the compounds evaluated in this study.
Data correspond to three representative organisms: Vibrio alginolyticus (blue squares), Fusarium sp. (red triangles) and Phaeodactylum tricornutum (green circles). Dotted lines show the cLogP of each compound, whose ID. number is indicated above. Missing symbols indicate lack of activity.
Fig 4.
Quorum sensing circuits of Chromobacterium violaceum (A) and Vibrio harveyi (B).
In C. violaceum ATCC 31532 (A), the synthase CviI produces the AI molecule HHL that is recognized by the cytoplasmatic receptor CviR. When bound to HHL, CviR dimerizes and binds DNA, leading to the expression of QS-regulated genes, including those involved in violacein production. In V. harveyi (B), three different AIs, synthesized by LuxM, LuxS and CqsA are recognized by the transmembrane two-component receptors LuxN, LuxPQ and CqsS, respectively. At low AI concentrations, these receptors act as kinases, phosphorylating LuxU and subsequently the σ54-dependent response regulator LuxO. The phosphorylated LuxO activate the transcription of Qrr sRNAs that together with the chaperone Hfq, destabilize the mluxR RNA. At high AI concentrations, the receptors switch to phosphatases and the expression of the master regulator LuxR is allowed.
Fig 5.
Dose-response curves for compounds 3–5 and 7 on C. violaceum CVO26 growth (A) and violacein synthesis (B).
Data represent the mean ± SD (N = 3).
Fig 6.
Growth curves of C. violaceum CVO26 in the presence of compounds 3 (A), 4 (B), 5 (C) and 7 (D).
Serial two-fold dilutions of the compounds from 500 to 7.8 μM were tested. A detailed version of this Fig is provided (S2 Fig).
Table 2.
Half-maximal inhibitory concentrations (μM) for the tested compounds on the growth and violacein production of C. violaceum CVO26.
Fig 7.
Bioluminescence (solid lines) and growth curves (dotted lines) for compounds 3–5 and 7 in V. harveyi.
Compound 3 (A-D); compound 4 (E-H); compound 5 (I-L); compound 7 (M-P). Serial two-fold dilutions of the compounds from 500 to 7.8 μM were tested.
Table 3.
IC50 values (μM) for luminescence and growth inhibitions caused by compounds 3–5 and 7 in V. harveyi WT and reporter strains.
Fig 8.
Relative luminescence ratios (Light units/OD600) for compounds 3–5 and 7 in V. harveyi.
WT (A), BB886 (B), BB170 (C) and BB721 (D). Serial two-fold dilutions of the compounds from 500 to 7.8 μM were tested.
Table 4.
Tyrosinase IC50 values (μM) for the compounds tested in this study.
Fig 9.
Lineweaver-Burk plots for tyrosinase inhibition in the presence of compound 16.
Data represent the mean ± SD (N = 3).
Fig 10.
Fluorescence spectra of tyrosinase under 280 nm excitation at different concentrations of 16.
The denatured and uninhibited enzyme were included as controls. Inset: Stern-Volmer plot of the fluorescence quenching.
Fig 11.
Decay of the fluorescence of tyrosinase tryptophan residues at different concentrations of compound 16.
IRF is the instrumental response function.
Fig 12.
Dose-response curves for compunds 3 and 16 in mussel (Mytilus galloprovincialis) foot retraction assays.
Fig 13.
The different colors highlight the main bioactivities and the structure-activity relationships of the tested triphenylphosphonium salts.