Natural products as antifouling compounds: recent progress and future perspectives

Anti-biofilm effect of a butenolide/polymer coating and metatranscriptomic analyses

Butenolide is an environmentally friendly antifouling natural product, but its efficiency and mechanism in preventing biofilm formation have not been examined. Furthermore, controlling the release of butenolide from paints into seawater is technically challenging. A coating was developed by mixing butenolide with a biodegradable polymer, poly (ε-caprolactone)-based polyurethane, and a one-month in situ anti-biofilm test was conducted in a subtidal area. The constant release of butenolide from the surface suggested that its release was well controlled. Direct observation and confocal microscope investigation indicated that the coating was effective against both biofilm formation and attachment of large fouling organisms. Metatranscriptomic analysis of biofilm samples implied that the coating selectively inhibited the adhesion of microbes from a variety of phyla and targeted particular functional pathways including energy metabolism, drug transport and toxin release. These integrated analyses demonstrated the potential application of this butenolide/polymer coating as an anti-biofilm material.

Environmentally benign antifouling activity and toxic properties of bioactive metabolites from mangrove Excoecaria agallocha L

This study was aimed to investigate the antifouling (AF) potentials and toxic properties of methanol extract from leaves of mangrove Excoecaria agallocha. Antimicrofouling activity results inferred that this extract strongly inhibited fouling bacterial and microalgal growth. This extract had also inhibited the settlement of brown mussel Perna indica and larvae of barnacle Balanus amphitrite. Further, EC₅₀ < LC₅₀ and therapeutic ratio > 1 together propagated non-toxic nature of the extract. Mollusk foot adherence assay result showed complete inhibition of foot spreading and loss of attachment of common rocky fouler Patella vulgata to the substrata. Field assay results affirmed that this extract effectively deterred settlement of biofoulers. Purification and GC-MS analysis of bioassay-guided active spot evidenced presence of three major compounds (> 85%) responsible for the promising AF activity. The identified lead compounds subjected to an estimation (BIOWIN™) program developed by United States Environmental Protection Agency (USEPA) predicts that they are biodegradable in nature. Graphical abstract.

Capsaicin-Inspired Thiol-Ene Terpolymer Networks Designed for Antibiofouling Coatings

Novel photocurable ternary polymer networks were prepared by incorporating N-(4-hydroxy-3-methoxybenzyl)-acrylamide (HMBA) into a cross-linked thiol-ene network based on poly(ethylene glycol)diacrylate (PEGDA) and (mercaptopropyl)methylsiloxane homopolymers (MSHP). The ternary network materials displayed bactericidal activity against Escherichia coli and Staphylococcus aureus and reduced the attachment of marine organism Phaeodactylum tricornutum. Extensive soaking of the polymer networks in aqueous solution indicated that no active antibacterial component leached out of the materials, and thus the ternary thiol-ene coating killed the bacteria by surface contact. The surface structures of the polymer networks with varied content ratios were studied by sum frequency generation (SFG) vibrational spectroscopy. The results demonstrated that the PDMS Si-CH₃ groups and mimic-capsaicine groups are predominantly present at the polymer-air interface of the coatings. Surface reorganization was apparent after polymers were placed in contact with D₂O: the hydrophobic PDMS Si-CH₃ groups left the surface and returned to the bulk of the polymer networks, and the hydrophilic PEG chains cover the polymer surfaces in D₂O. The capasaicine methoxy groups are able to segregate to the surface in an aqueous environment, depending upon the ratio of HMBA/PEGDA. SFG measurements in situ showed that the antibacterial HMBA chains, rather than the nonfouling PEG, played a dominant role in mediating the antibiofouling performance in this particular polymer system.

Minireview: algal natural compounds and extracts as antifoulants

Marine biofouling is a paramount phenomenon in the marine environment and causes serious problems to maritime industries worldwide. Marine algae are known to produce a wide variety of chemical compounds with antibacterial, antifungal, antialgal, and anti-macrofouling properties, inhibiting the settlement and growth of other marine fouling organisms. Significant investigations and progress have been made in this field in the last two decades and several antifouling extracts and compounds have been isolated from micro- and macroalgae. In this minireview, we have summarized and evaluated antifouling compounds isolated and identified from macroalgae and microalgae between January 2010 and June 2016. Future directions for their commercialization through metabolic engineering and industrial scale up have been discussed. Upon comparing biogeographical regions, investigations from Southeast Asian waters were found to be rather scarce. Thus, we have also discussed the need to conduct more chemical ecology based research in relatively less explored areas with high algal biodiversity like Southeast Asia.

An antifouling model from the sea: a review of 25 years of zosteric acid studies

Many studies have shown that natural marine compounds can prevent biofouling by a broad spectrum of organisms without toxic effects, encouraging their use in antifouling (AF) coatings. Studies over the past 25 years of the natural product zosteric acid (ZA) are systematically organized in this review. ZA is a sulfated phenolic acid produced by the seagrass Zostera marina that has very promising AF potential against several micro- and macrofouling organisms. ZA was shown to have appropriate environmental fate parameters such as high water solubility, a low log P, low bioaccumulation, and no ecotoxicity, which demonstrated the potential of ZA as a safe AF agent. This review also highlights that ZA has been successfully incorporated into several types of coatings. The synthesis of analogs is also considered in this review, and it has allowed a better understanding of ZA structure-AF activity relationships and clarified the mechanism of action of ZA.

Antifouling Compounds from Marine Invertebrates

In this review, a comprehensive overview about the antifouling compounds from marine invertebrates is described. In total, more than 198 antifouling compounds have been obtained from marine invertebrates, specifically, sponges, gorgonian and soft corals.

Mini-Review: Antifouling Natural Products from Marine Microorganisms and Their Synthetic Analogs

Biofouling causes huge economic loss and generates serious ecological issues worldwide. Marine coatings incorporated with antifouling (AF) compounds are the most common practices to prevent biofouling. With a ban of organotins and an increase in the restrictions regarding the use of other AF alternatives, exploring effective and environmentally friendly AF compounds has become an urgent demand for marine coating industries. Marine microorganisms, which have the largest biodiversity, represent a rich and important source of bioactive compounds and have many medical and industrial applications. This review summarizes 89 natural products from marine microorganisms and 13 of their synthetic analogs with AF EC50 values ≤ 25 μg/mL from 1995 (the first report about marine microorganism-derived AF compounds) to April 2017. Some compounds with the EC50 values < 5 μg/mL and LC50/EC50 ratios > 50 are highlighted as potential AF compounds, and the preliminary analysis of structure-relationship (SAR) of these compounds is also discussed briefly. In the last part, current challenges and future research perspectives are proposed based on opinions from many previous reviews. To provide clear guidance for the readers, the AF compounds from microorganisms and their synthetic analogs in this review are categorized into ten types, including fatty acids, lactones, terpenes, steroids, benzenoids, phenyl ethers, polyketides, alkaloids, nucleosides and peptides. In addition to the major AF compounds which targets macro-foulers, this review also includes compounds with antibiofilm activity since micro-foulers also contribute significantly to the biofouling communities.

Antifouling Compounds from Marine Macroalgae

Marine macroalgae produce a wide variety of biologically-active metabolites that have been developed into commercial products, such as antibiotics, immunosuppressive, anti-inflammatory, cytotoxic agents, and cosmetic products. Many marine algae remain clean over longer periods of time, suggesting their strong antifouling potential. Isolation of biogenic compounds and the determination of their structure could provide leads for the development of environmentally-friendly antifouling paints. Isolated substances with potent antifouling activity belong to fatty acids, lipopeptides, amides, alkaloids, lactones, steroids, terpenoids, and pyrroles. It is unclear as yet to what extent symbiotic microorganisms are involved in the synthesis of these compounds. Algal secondary metabolites have the potential to be produced commercially using genetic and metabolic engineering techniques. This review provides an overview of publications from 2010 to February 2017 about antifouling activity of green, brown, and red algae. Some researchers were focusing on antifouling compounds of brown macroalgae, while metabolites of green algae received less attention. Several studies tested antifouling activity against bacteria, microalgae and invertebrates, but in only a few studies was the quorum sensing inhibitory activity of marine macroalgae tested. Rarely, antifouling compounds from macroalgae were isolated and tested in an ecologically-relevant way.

Pyomelanin from Pseudoalteromonas lipolytica reduces biofouling

Members of the marine bacterial genus Pseudoalteromonas are efficient producers of antifouling agents that exert inhibitory effects on the settlement of invertebrate larvae. The production of pigmented secondary metabolites by Pseudoalteromonas has been suggested to play a role in surface colonization. However, the physiological characteristics of the pigments produced by Pseudoalteromonas remain largely unknown. In this study, we identified and characterized a genetic variant that hyperproduces a dark‐brown pigment and was generated during Pseudoalteromonas lipolytica biofilm formation. Through whole‐genome resequencing combined with targeted gene deletion and complementation, we found that a point mutation within the hmgA gene, which encodes homogentisate 1,2‐dioxygenase, is solely responsible for the overproduction of the dark‐brown pigment pyomelanin. In P. lipolytica, inactivation of the hmgA gene led to the formation of extracellular pyomelanin and greatly reduced larval settlement and metamorphosis of the mussel Mytilus coruscus. Additionally, the extracted pyomelanin from the hmgA deletion mutant and the in vitro‐synthesized pyomelanin also reduced larval settlement and metamorphosis of M. coruscus, suggesting that extracellular pyomelanin released from marine Pseudoalteromonas biofilm can inhibit the settlement of fouling organisms.

Monitoring the magnitude of marine vessel infestation by non-indigenous ascidians in the Mediterranean

Invasive ascidians (Chordata, Tunicata) are dominant nuisance organisms. The current study investigated the role of marine vessels in their dispersal and introduction. An examination of 45 dry-docked marine vessels, comprising recreational, commercial, and military craft, in five Israeli shipyards along the Mediterranean coast, revealed non-indigenous ascidians (NIA) on every second vessel investigated. Military vessels featured the highest ascidian abundance and richness, potentially related to their maintenance routine. Niche areas on the vessels such as sea chests and the propeller exhibited the highest occurrence of ascidians. Overall, these findings provide strong evidence that marine vessels play an acute role in NIA introduction and dispersal, with military vessels and niche areas on all the vessels being more susceptible to serving as vectors. A discovery of a new introduced species during the surveys suggests that the monitoring of marine vessels can serve as an effective tool for the early detection of NIA.

Unusual Inner-Salt Guaiazulene Alkaloids and bis-Sesquiterpene from the South China Sea Gorgonian Muriceides collaris

Three new guaiazulene alkaloids muriceidines A–C (1–3) and one new bis-sesquiterpene muriceidone A (4), were isolated from the South China Sea gorgonian Muriceides collaris. Muriceidines are the first examples structurally architected by guaiazulene coupling with an inner-salt Δ¹-pipecolic acid via a unique sp² methine-bridged linkage, and the bis-sesquiterpene was comprised by a guaiazulene and a indene units linked through a unprecedented carbon-carbon σ-bond between the high steric bridgehead carbon C-10 of guaiazulene moiety and C-2′ of indene moiety. The chiral compounds 2–4 were obtained initially as racemates and further separated by chiral HPLC methods. The inner-salt structures of 1–3 and absolute configurations of 2–4 were fully elucidated by calculated ¹³C NMR, ECD and OR with quantum chemical calculation methods. Compound 1 showed cytotoxicity against K562 cell lines with IC₅₀ value of 8.4 μM and antifouling activity against the larvae of the barnacle Balanus albicostatus with EC₅₀ value of 11.9 μg/mL and potent therapeutic index (LC₅₀/EC₅₀ = 3.66). Also the racemic (±)-3 showed cytotoxicities against both HL-60 and K562 cell lines with IC₅₀ values of 2.2 and 3.7 μM, respectively. A semisynthetic trial was performed to validate the proposed biosynthetic hypotheses.

Preparation, Structure, and Potent Antifouling Activity of Sclerotioramine Derivatives

A series of 30 sclerotioramine derivatives (2-31) of the natural compound, (+)-sclerotiorin (1), has been successfully semi-synthesized by a one-step reaction with high yields (up to 80%). The structures of these new derivatives were established by extensive spectroscopic methods and single-crystal X-ray diffraction analysis for 3, 6, and 10. (+)-Sclerotiorin (1) and its semisynthetic derivatives (2-31) were evaluated for their antifouling activity. Most of them except 6, 7, 8, 12, and 28 showed potent antifouling activity against the larval settlement of the barnacle Balanus amphitrite. More interestingly, most of the aromatic amino-derivatives (13-17, 19-21, 23, 25-27, and 29-31) showed strong antifouling activity; however, only two aliphatic amino-derivatives (5 and 10) had the activity.

Anti-Biofilm Effect of Biodegradable Coatings Based on Hemibastadin Derivative in Marine Environment

Dibromohemibastadin-1 (DBHB) is an already known potent inhibitor of blue mussel phenoloxidase (which is a key enzyme involved in bioadhesion). Within this study, the potentiality of DBHB against microfouling has been investigated. The activity of DBHB was evaluated on key strains of bacteria and microalgae involved in marine biofilm formation and bioassays assessing impact on growth, adhesion and biofilm formation were used. To assess the efficiency of DBHB when included in a matrix, DBHB varnish was prepared and the anti-microfouling activity of coatings was assessed. Both in vitro and in situ immersions were carried out. Confocal Laser Scanning Microscopy (CLSM) was principally used to determine the biovolume and average thickness of biofilms developed on the coatings. Results showed an evident efficiency of DBHB as compound and varnish to reduce the biofilm development. The mode of action seems to be based principally on a perturbation of biofilm formation rather than on a biocidal activity in the tested conditions.

Design, Synthesis, and Antifouling Activity of Glucosamine-Based Isocyanides

Biofouling, an undesirable accumulation of organisms on sea-immersed structures such as ship hulls and fishing nets, is a serious economic issue whose effects include oil wastage and clogged nets. Organotin compounds were utilized since the 1960s as an antifouling material; however, the use of such compounds was later banned by the International Maritime Organization (IMO) due to their high toxicity toward marine organisms, resulting in masculinization and imposex. Since the ban, there have been extensive efforts to develop environmentally benign antifoulants. Natural antifouling products obtained from marine creatures have been the subject of considerable attention due to their potent antifouling activity and low toxicity. These antifouling compounds often contain isocyano groups, which are well known to have natural antifouling properties. On the basis of our previous total synthesis of natural isocyanoterpenoids, we envisaged the installation of an isocyano functional group onto glucosamine to produce an environmentally friendly antifouling material. This paper describes an effective synthetic method for various glucosamine-based isocyanides and evaluation of their antifouling activity and toxicity against cypris larvae of the barnacle Amphibalanus amphitrite. Glucosamine isocyanides with an ether functionality at the anomeric position exhibited potent antifouling activity, with EC₅₀ values below 1 μg/mL, without detectable toxicity even at a high concentration of 10 μg/mL. Two isocyanides had EC₅₀ values of 0.23 and 0.25 μg/mL, comparable to that of CuSO₄, which is used as a fouling inhibitor (EC₅₀ = 0.27 μg/mL).

Antifouling potential of Nature-inspired sulfated compounds

Natural products with a sulfated scaffold have emerged as antifouling agents with low or nontoxic effects to the environment. In this study 13 sulfated polyphenols were synthesized and tested for antifouling potential using the anti-settlement activity of mussel (Mytilus galloprovincialis) plantigrade post-larvae and bacterial growth inhibition towards four biofilm-forming bacterial strains. Results show that some of these Nature-inspired compounds were bioactive, particularly rutin persulfate (2), 3,6-bis(β-D-glucopyranosyl) xanthone persulfate (6), and gallic acid persulfate (12) against the settlement of plantigrades. The chemical precursors of sulfated compounds 2 and 12 were also tested for anti-settlement activity and it was possible to conclude that bioactivity is associated with sulfation. While compound 12 showed the most promising anti-settlement activity (EC₅₀ = 8.95 μg.mL⁻¹), compound 2 also caused the higher level of growth inhibition in bacteria Vibrio harveyi (EC₂₀ = 12.5 μg.mL⁻¹). All the three bioactive compounds 2, 6, and 12 were also found to be nontoxic to the non target species Artemia salina (<10% mortality at 250 μM) and Vibrio fischeri (LC₅₀ > 1000 μg.mL⁻¹). This study put forward the relevance of synthesizing non-natural sulfated small molecules to generate new nontoxic antifouling agents.

Polymeric Quaternary Ammonium-Containing Coatings with Potential Dual Contact-Based and Release-Based Antimicrobial Activity

In the present work, reactive blending of copolymers with complementary functional groups was applied to control their antimicrobial activity and antifouling action in real conditions. For this purpose, two series of copolymers, poly(4-vinylbenzyl chloride-co-acrylic acid), P(VBC-co-AAx), and poly(sodium 4-styrenesulfonate-co-glycidyl methacrylate), P(SSNa-co-GMAx), were synthesized via free radical copolymerization and further modified by the incorporation of biocidal units either covalently (4-vinyl benzyl dimethylhexadecylammonium chloride, VBCHAM) or electrostatically bound (cetyltrimethylammonium 4-styrenesulfonate, SSAmC₁₆). The cross-linking reaction of the carboxylic group of acrylic acid (AA) with the epoxide group of glycidyl methacrylate (GMA) of these two series of reactive antimicrobial copolymers was explored in blends obtained through solution casting after curing at various temperatures. The combined results from the ATR-FTIR characterization of the membranes, solubility tests, turbidimetry, and TEM suggest that the reaction occurs already at 80 °C, leading mostly to graft samples, while at higher curing temperatures (120 or 150 °C) insoluble cross-linked samples are usually obtained. Controlled release experiments of selected membranes were performed in pure water and aqueous 1 M NaCl solutions for a period of two months. The released material was followed through gravimetry and TOC/TN measurements, while the evolution of the integrity and the morphology of the membranes were followed visually and through SEM, respectively. Antimicrobial tests also revealed that the cross-linked membranes presented strong antimicrobial activity against S. aureus and P. aeruginosa. Finally, a specific blend combination was applied on aquaculture nets and cured at 80 °C. The modified nets, emerged in the sea for 15 and 35 days, exhibited high antifouling action as compared to blank nets.

Antifouling phenyl ethers and other compounds from the invertebrates and their symbiotic fungi collected from the South China Sea

Marine organism-derived secondary metabolites are promising potential sources for discovering environmentally safe antifouling agents. In present study, 55 marine secondary metabolites and their synthesized derivatives were tested and evaluated for their antifouling activities and security. These compounds include 44 natural products isolated from marine invertebrates and their symbiotic microorganisms collected from the South China Sea and 11 structural modified products derived from the isolated compounds. The natural secondary metabolites, covering phenyl ether derivatives, terpenoids, 9, 11-secosteroids, anthraquinones, alkaloids, nucleoside derivatives and peptides, were isolated from two corals, one sponge and five symbiotic fungi. All of the isolated and synthesized compounds were tested for their antifouling activities against the cyprids of barnacle Balanus (Amphibalanus) amphitrite Darwin. Noticeably, five phenyl ether derivatives (9, 11, 13-15) exhibited potent anti-larval settlement activity with the EC50 values lower than 3.05 μM and the LC50/EC50 ratios higher than 15. The study of structure-activity relationship (SAR) revealed that the introduction of acetoxy groups and bromine atoms to phenyl ether derivatives could significantly improve their antifouling activities. This is the first report on the SAR of phenyl ether derivatives on antifouling activity against barnacle B. amphitrite. The polybrominated diphenyl ether derivative, 2, 4, 6, 2', 4', 6'-hexabromo-diorcinol (13), which displayed excellent antifouling activity, was considered as a promising candidate of environmentally friendly antifouling agents.

Anti-barnacle Activity of Isocyanides Derived from Amino Acids

Creation of new potent antifouling active compounds is important for the development of environmentally friendly antifouling agents. Fifteen isocyanide congeners derived from proteinogenic amino acids were synthesized, and the antifouling activity and toxicity of these compounds against cypris larvae of the barnacle Balanus amphitrite were investigated. All synthesized amino acid-isocyanides exhibited potent anti-barnacle activity with EC₅₀ values of 0.07 - 10.34 μg/ml after 120 h exposure without significant toxicity. In addition, seven compounds showed more than 95% settlement inhibition of the cypris larvae at 10 μg/ml after 120 h exposure without any mortality observed. Considering their structure, these amino acid-isocyanides would eventually be biodegraded to their original nontoxic amino acids. These should be useful for further research focused on the development of environmentally friendly antifoulants.

Screening of bromotyramine analogues as antifouling compounds against marine bacteria

Rapid and efficient synthesis of 23 analogues inspired by bromotyramine derivatives, marine natural products, by means of CuSO4-catalysed [3+2] alkyne-azide cycloaddition is described. The final target was then assayed for anti-biofilm activity against three Gram-negative marine bacteria, Pseudoalteromonas ulvae (TC14), Pseudoalteromonas lipolytica (TC8) and Paracoccus sp. (4M6). Most of the synthesised bromotyramine/triazole derivatives are more active than the parent natural products Moloka'iamine (A) and 3,5-dibromo-4-methoxy-β-phenethylamine (B) against biofilm formation by the three bacterial strains. Some of these compounds were shown to act as non-toxic inhibitors of biofilm development with EC50 < 200 μM without any effect on bacterial growth even at high concentrations (200 μM).

Synthetic biology to access and expand nature's chemical diversity

Bacterial genomes encode the biosynthetic potential to produce hundreds of thousands of complex molecules with diverse applications, from medicine to agriculture and materials. Accessing these natural products promises to reinvigorate drug discovery pipelines and provide novel routes to synthesize complex chemicals. The pathways leading to the production of these molecules often comprise dozens of genes spanning large areas of the genome and are controlled by complex regulatory networks with some of the most interesting molecules being produced by non-model organisms. In this Review, we discuss how advances in synthetic biology--including novel DNA construction technologies, the use of genetic parts for the precise control of expression and for synthetic regulatory circuits--and multiplexed genome engineering can be used to optimize the design and synthesis of pathways that produce natural products.

Antifouling Activity of Lipidic Metabolites Derived from Padina tetrastromatica

An attempt has been made to identify the potential seaweed for antifouling property due to the growing need for environmentally safe antifouling systems. The antibacterial, antimicroalgal, and antimussel foot adherence potentials of methanol, dichloromethane, and hexane extracts of the chosen seaweeds such as Padina tetrastromatica, Caulerpa taxifolia, and Amphiroa fragilissima have been compared against copper sulfate. Among the extracts, the maximum antibacterial activities were exhibited by the methanol extract of P. tetrastromatica. The minimum inhibitory concentration (MIC) of the methanolic extract of P. tetrastromatica was found to be 10 and 1 μg/ml against test biofilm bacteria and diatoms, respectively. The antimussel foot adherence assay indicated that the extract had inhibited the foot adherence of the green mussels Perna viridis with the effective concentration (EC50) of 25.51 ± 0.03 μg/ml, and lethal concentration for 50 % mortality (LC50) was recorded at 280.22 ± 0.12 μg/ml. Based on the prolific results, the crude methanolic extract of P. tetrastromatica was subjected to purification using silica gel column and thin-layer chromatography (TLC). Then, the active compounds of the bioassay-guided fraction (F13) were identified using gas chromatography coupled with mass spectroscopy (GC-MS), and it was observed that fatty acids were the major components, which may be responsible for the antifouling properties.

Antibiofouling potential of quercetin compound from marine-derived actinobacterium, Streptomyces fradiae PE7 and its characterization

An attempt has been made to isolate, purify and characterize antifouling compound from Streptomyces fradiae PE7 isolated from Vellar estuarine sediment, Parangipettai, South India. The microbial identification was done at species level based on its phenotypic, cell wall and molecular characteristics. Strain PE7 produced high quantity of antifouling compounds in agar surface fermentation when compared to submerged fermentation. In fermentation optimization, wide range of sugars, amino acids, minerals, pH, temperature and NaCl concentration was found to influence the antifouling compound production from the strain PE7. Antifouling compound PE7-C was purified from the crude extract by preparative TLC, and its activity against biofouling bacteria was confirmed by bioautography. Based on the physico-chemical characteristics, the chemical structure of the antifouling compound PE7-C was identified as quercetin (C15H10O7), a flavonoid class of compound with the molecular weight 302.23 g/mol. The purified quercetin was active against 18 biofouling bacteria with MIC range between 1.6 and 25 μg/ml, algal spore germination and mollusc foot adherence found at 100 μg/ml and 306 ± 19.6 μg ml(-1) respectively. The present study, for the first time, reported quercetin from marine-derived Streptomyces sp. PE7 with antifouling activity. This also leads to the repurposing of quercetin for the development of antifouling agent.

Fouling-release and chemical activity effects of a siloxane-based material on tunicates

The antifouling performance of a siloxane-based elastomeric impression material (EIM) was compared to that of two silicone fouling-release coatings, Intersleek 757 and RTV-11. In field immersion trials, the EIM caused the greatest reduction in fouling by the solitary tunicate Ciona intestinalis and caused the longest delay in the progression of fouling by two species of colonial tunicate. However, in pseudobarnacle adhesion tests, the EIM had higher attachment strengths. Further laboratory analyses showed that the EIM leached alkylphenol ethoxylates (APEs) that were toxic to C. intestinalis larvae. The EIM thus showed the longest duration of chemical activity measured to date for a siloxane-based coating (4 months), supporting investigations of fouling-release coatings that release targeted biocides. However, due to potential widespread effects of APEs, the current EIM formulation should not be considered as an environmentally-safe antifoulant. Thus, the data also emphasize consideration of both immediate and long-term effects of potentially toxic constituents released from fouling-release coatings.

Antifouling activity of green-synthesized 7-hydroxy-4-methylcoumarin

In the search for new environmental-friendly antifoulants for replace metallic biocides, 7-hydroxy-4-methylcoumarin was synthesized according to green chemistry procedures. This compound was characterized by current organic analysis and its antifouling properties were firstly evaluated on the bivalve Mytilus edulis platensis in the laboratory. In the second stage, a soluble matrix antifouling coating formulated with this compound was assayed in marine environment. Laboratory experiments showed that 7-hydroxy-4-methylcoumarin was effective in inhibiting both the settlement as well as the byssogenesis of mussels. In addition, after exposure time in the sea, painted panels containing this compound showed strong antifouling effect on conspicuous species of the fouling community of Mar el Plata harbor. In conclusion, green-synthesized coumarin could be a suitable antifoulant candidate for marine protective coatings.

Cochliomycin A inhibits the larval settlement of Amphibalanus amphitrite by activating the NO/cGMP pathway

Cochliomycin A is a compound with anti-barnacle settlement activity and low toxicity, but the molecular mechanism of the compound is unknown. Here, isobaric tags for the relative or absolute quantitation (iTRAQ) labeling proteomic method were applied to analyze changes in the proteome of Amphibalanus (=Balanus) amphitrite cyprids in response to cochliomycin A treatment. Cochliomycin A affected the cytochrome P450, glutathione S-transferase (GST) and NO/cGMP pathways, among which the NO/cGMP pathway was considered to play a key role in barnacle larval settlement, while the cytochrome P450 and the GST pathways are mainly for detoxification. The results of real-time PCR further suggested the NO/cGMP pathway was activated in response to cochliomycin A. Larval settlement assays revealed that S-methylisothiourea sulfate (SMIS) and 1H-(1,2,4)oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) rescued cyprids from cochliomycin A-induced inhibition of larval settlement. The findings supported the hypothesis that cochliomycin A inhibited barnacle larval settlement by stimulating the NO/cGMP pathway.

Effects of surface-active block copolymers with oxyethylene and fluoroalkyl side chains on the antifouling performance of silicone-based films

Block copolymers made from a poly(dimethyl siloxane) (Si) and a poly(meth)acrylate carrying oxyethylene (EG) or fluoroalkyl (AF) side chains were synthesized and incorporated as surface-active components into a silicone matrix to produce cross-linked films with different surface hydrophilicity/phobicity. Near-edge X-ray absorption fine structure (NEXAFS) studies showed that film surfaces containing Si-EG were largely populated by the siloxane, with the oxyethylene chains present only to a minor extent. In contrast, the fluorinated block was selectively segregated to the polymer-air interface in films containing Si-AF as probed by NEXAFS and X-ray photoelectron spectroscopy (XPS) analyses. Such differences in surface composition were reflected in the biological performance of the coatings. While the films with Si-EG showed a higher removal of both Ulva linza sporelings and Balanus amphitrite juveniles than the silicone control, those with Si-AF exhibited excellent antifouling properties, preventing the settlement of cyprids of B. amphitrite.

Characterization and anti-biofilm activity of extracellular polymeric substances produced by the marine biofilm-forming bacterium Pseudoalteromonas ulvae strain TC14

This study investigated soluble (Sol-EPS), loosely bound (LB-EPS), and tightly bound extracellular polymeric substances (TB-EPS) harvested from biofilm and planktonic cultures of the marine bacterium Pseudoalteromonas ulvae TC14. The aim of the characterization (colorimetric methods, FTIR, GC-MS, NMR, HPGPC, and AFM analyses) was to identify new anti-biofilm compounds; activity was assessed using the BioFilm Ring Test®. A step-wise separation of EPS was designed, based on differences in water-solubility and acidity. An acidic fraction was isolated from TB-EPS, which strongly inhibited biofilm formation by marine bacterial strains in a concentration-dependent manner. The main constituents of this fraction were characterized as two glucan-like polysaccharides. An active poly(glutamyl-glutamate) fraction was also recovered from TB-EPS. The distribution of these key EPS components in Sol-EPS, LB-EPS, and TB-EPS was distinct and differed quantitatively in biofilm vs planktonic cultures. The anti-biofilm potential of the fractions emphasizes the putative antifouling role of EPS in the environment.

Desiccation as a mitigation tool to manage biofouling risks: trials on temperate taxa to elucidate factors influencing mortality rates

The desiccation tolerance of biofouling taxa (adults and early life-stages) was determined under both controlled and 'realistic' field conditions. Adults of the ascidian Ciona spp. died within 24 h. Mortality in the adult blue mussel Mytilus galloprovincialis occurred within 11 d under controlled conditions, compared with 7 d when held outside. The Pacific oyster Crassostrea gigas was the most desiccation-tolerant taxon tested (up to 34 d under controlled conditions). Biofouling orientated to direct sunlight showed faster mortality rates for all the taxa tested. Mortality in Mytilus juveniles took up to 24 h, compared with 8 h for Ciona, with greater survival at the higher temperature (18.5°C) and humidity (~95% RH) treatment combination. This study demonstrated that desiccation can be an effective mitigation method for a broad range of fouling taxa, especially their early life-stages. Further work is necessary to assess risks from other high-risk species such as algae and cyst forming species.

Antifouling assessments on biogenic nanoparticles: A field study from polluted offshore platform

Turbinaria ornata mediated silver nanoparticles (TOAg-NPs) were evaluated for antibacterial activity against 15 biofilm forming bacterial isolates. A field study in natural seawater for 60 days showed antifouling activity of TOAg-NPs on stainless steel coupons (SS-304) coated with Apcomin zinc chrome (AZC) primer. Though TOAg-NPs showed broad spectrum of antibacterial activity, the maximum zone of inhibition was with Escherichiacoli (71.9%) and a minimum with Micrococcus sp. (40%) due to the EPS secretion from Gram-positive bacteria. Compared to control coupons (18.9 [ × 10(3)], 67.0 [× 10(3)], 13.5 [ × 10(4)] and 24.7 [ × 10(4)]CFU/cm(2)), experimental biocide coupons (71.0 [ × 10(2)], 32.0 [ × 10(3)], 82.0 [ × 10(3)] and 11.3 [ × 10(4)]CFU/cm(2)) displayed lesser bacterial population density. Toxicity studies revealed 100% mortality for Balanus amphitrite larvae at 250 μg ml(-1) concentration within 24h, while 56.6% recorded for Artemia marina at the same concentration indicating less toxicity to non target species. It proved that AZC+TOAg-NPs prevent biofouling by its Ag-NS affinity and antimicrobial effectivity.

Potent Antifouling Marine Dihydroquinolin-2(1H)-one-Containing Alkaloids from the Gorgonian Coral-Derived Fungus Scopulariopsis sp

Marine biofouling has a major economic impact, especially when it occurs on ship hulls or aquaculture facilities. Since the International Maritime Organization (IMO) treaty to ban the application of organotin-based paints to ships went into effect in 2008, there is an urgent demand for the development of efficient and environmentally friendly antifouling agents. Marine microorganisms have proved to be a potential source of antifouling natural compounds. In this study, six dihydroquinolin-2-one-containing alkaloids, three monoterpenoids combined with a 4-phenyl-3,4-dihydroquinolin-2(1H)-one (1-3) and three 4-phenyl-3,4-dihydroquinolin-2(1H)-one alkaloids (4-6), were isolated from the gorgonian coral-derived fungus Scopulariopsis sp. collected in the South China Sea. These dihydroquinolin-2-one-containing alkaloids were evaluated against the larval settlement of barnacle Balanus amphitrite, and antifouling activity was detected for the first time for this class of metabolites. All of them except 6 showed strong antifouling activity. Compounds 1 and 2 were discovered to be the most promising non-toxic antilarval settlement candidates. Especially, compound 1 is the strongest antifouling compound in nature until now which showed highly potent activity with picomolar level (EC50 17.5 pM) and a very safety and high therapeutic ratio (LC50/EC50 1200). This represents an effective non-toxic, anti-larval settlement structural class of promising antifouling lead compound.

Antifouling activity in some benthic Antarctic invertebrates by "in situ" experiments at Deception Island, Antarctica

Competition for space is a remarkable ecological force, comparable to predation, producing a strong selective pressure on benthic invertebrates. Some invertebrates, thus, possess antimicrobial compounds to reduce surface bacterial growth. Antimicrobial inhibition is the first step in avoiding being overgrown by other organisms, which may have a negative impact in feeding, respiration, reproduction … The in situ inhibition of bacterial biofilm was used here as an indicator of antifouling activity by testing hydrophilic extracts of twelve Antarctic invertebrates. Using two different approaches (genetics and confocal techniques) different levels of activity were found in the tested organisms. In fact, differences within body parts of the studied organisms were determined, in agreement with the Optimal Defense Theory. Eight out of 15 extracts tested had negative effects on fouling after 28 days submerged in Antarctic waters. Thus, although chemical defenses may be quite species-specific in their ecological roles, these results suggest that different chemical strategies exist to deal with space competition.