Biofouling is a major drawback in the marine industry. As the use of the toxic antifouling coatings has been restricted due to their negative environmental impact, the development of environmentally friendly, biocide-free alternative is necessary. Hydrogel coatings based on polysaccharides are an alternative that is attracting a great deal of attention. These coatings are considered a promising material because they are environmentally friendly and the dense hydration layer protects the substrate from biofouling. This study reports on optimized hydrogel coatings based on chitosan that improve their antifouling performance by incorporating a hydrophilic polysaccharide. This study compares the performance of a bacterial exopolysaccharide from Vibrio MO245 with that of the well-known hyaluronic acid. After presenting the preparation of the coatings, including the depolymerization of MO245, the coatings characterize using topography measurement, crosslinking analysis, hydration capacity analysis and hydrophobicity analysis. The efficiency of the coatings is then evaluated against three representative organisms: the bacterium Vibrio harveyi, the diatoms Cylindrotheca closterium and the larvae Magallana gigas.

Diatoms constitute the main photosynthetic group in marine biofilms throughout the world's oceans, in particular, on plastic debris, which has become a major problem in the marine environment. However, they remain largely unexplored in this context compared to prokaryotes. Here, we aim to understand the dynamics of diatom communities in the plastisphere at different levels: how taxa are selected from the planktonic community and how communities are structured over time and at large spatial scales. Biofilms were collected from PVC (polyvinyl chloride) panels immersed (i) for 1 year in two NW Mediterranean sites, a mesotrophic one (Toulon Bay) and an oligotrophic one (Banyuls Bay), and (ii) for 1 month in Toulon Bay and two other eutrophic sites (Lorient in South Brittany in the Atlantic Ocean and Reunion Island in the Indian Ocean). Plastispheres were analyzed using both microscopic and molecular approaches, focusing on the relationship between diatoms and other microorganisms in biofilms. Light microscopy revealed spatio-temporal differences in cell abundance and biovolume. Metabarcoding, targeting the rbcL gene for diversity and composition, revealed that the richness of diatom species was already maximal in the early stages of biofilm formation, and beta-diversity showed a clear temporal evolution in the Mediterranean Sea. Including prokaryotic and fungal communities, we described microorganism interactions within biofilms throughout the colonization process of the plastisphere. In addition, environmental parameters on a large geographical scale were shown to be stronger drivers in structuring diatom communities, considering both planktonic and biofilm lifestyles. A core biofilm community represented by a few abundant species was observed across sites. The occurrence of tychoplanktonic taxa emphasizes the specificity of diatoms among other microorganisms in biofilms. Finally, the complete absence of common genetic variants among Lorient, Reunion Island, and Toulon suggests that dispersal by marine currents over a large geographical scale has led to adaptation processes.

Since 2011, massive strandings of Sargassum (brown alga) have significantly affected Caribbean islands causing major health, environmental and economic problems. Amongst them, the degradation of algae releases corrosive gases, hydrogen sulphide (H2S) and ammonia (NH3) which causes an accelerated corrosion of the metallic structures of these coastal areas. The aim of this study was to quantify the impact of Sargassum strandings on the corrosion of three types of steels (DC01 carbon steel, 304L and 316L stainless steels) immersed for up to 120 days at various sites in Martinique which were gradually impacted by Sargassum. A multidisciplinary approach was developed, incorporating: (i) surface analysis through macrophotography and corrosion product examination, (ii) weight loss measurements, and (iii) analysis of physicochemical parameters alongside microbial composition. As a result, in the presence of degraded Sargassum, an anaerobic, reducing and more acidic environment was correlated with high corrosion rates for all studied steels. When high density of Sargassum sp. was present, elemental sulphur was identified in the corrosion product layers of DC01 and 316L. Moreover, in this condition, sulphate-reducing bacteria (SRB) were observed in the surface biofilms of 304L coupons such as Desulfobulbus rhabdoformis. All these factors have highlighted the aggressiveness of the medium resulting from the presence of decomposing Sargassum, leading to increased corrosion rates. Our work provides new information on the importance of managing Sargassum strandings in order to avoid accelerated degradation of metallic structures in harbours and coastal zones.

The aim of this work is to investigate the effect of ultra-soft hydrogel coatings on bacterial adhesion. To achieve this, chitosan hydrogel coatings were prepared and characterized in terms of physicochemical surface properties (roughness, hydrophobicity), mechanical characteristics (elastic modulus, crosslink density), as well as their hydration and swelling capacities. Physicochemical properties, such as roughness and hydrophobicity, were confirmed to remain consistent. Two model marine bacterial strains, a non-motile Gram-positive Bacillus sp. 4J6 and a motile Gram-negative Vibrio harveyi, were selected for this study. The assessment of their adhesion on the coatings was performed under flow and analyzed by confocal laser scanning microscopy. The results suggest that bacterial adhesion decreases as the amount of cross-linking agent (citric acid) is reduced, while changes in hydration, swelling rates and stiffness (elastic modulus) - all influenced by the degree of cross-linking - were less pronounced. Notably, the variations in elastic modulus (from 1.98 to 2.29 KPa), hydration (from 76 % to 62 %) and swelling rate (from 125 % to 65 %) after immersion in deionized water were remarkably minimal. This study highlights the complexity of understanding the mechanisms of bacterial adhesion to hydrogel coatings, challenges widely accepted views on the impact of stiffness on bacterial adhesion, and emphasizes the need to

The tightening of regulations on marine antifouling solutions is driving the demand for more environmentally friendly antifouling coatings. To meet this demand, two kinds of TiO2 photocatalytic surfaces consisting in thin films and microstructured films were synthesised and tested on the adhesion and biofilm formation of Vibrio harveyi. Aerosol-assisted metal organic chemical vapour deposition was used for the growth of these TiO2 layers. The microstructured films are characterised by the presence, on the top of TiO2 thin films, of hierarchical hemispherical microstructures formed by nanosheets and described as microflowers. Both thin films and microstructured films present a crystallisation in TiO2 anatase phase and are superhydrophilic. The photocatalytic activity increases by a factor of 10 in the presence of microflowers and the specific surface area increases by a factor of 170 when comparing both types of surfaces. The antifouling properties of TiO2 thin films and microstructured TiO2 films were tested for their effect on adhesion and biofilm formation of V. harveyi, a marine pathogen responsible for marine fouling. The role of the photocatalytic activity of these TiO2 surfaces was established by comparing the V. harveyi bacterial adhesion and biofilm maturation under illumination and in the dark. For both surfaces, bactericidal efficacy was observed under illumination during the adhesion stage; however, the presence of TiO2 microstructures enhanced significantly this effect. Furthermore, non-microstructured surfaces were specifically evaluated during biofilm formation, revealing antibiofilm activity after adhesion under illumination.

Confronting the challenge of biofilm resistance and widespread antimicrobial resistance (AMR), this study emphasizes the need for innovative monitoring methods and explores the potential of bacteriophages against bacterial biofilms. Traditional methods, like optical density (OD) measurements and confocal microscopy, crucial in studying biofilm–virus interactions, often lack real-time monitoring and early detection capabilities, especially for biofilm formation and low bacterial concentrations. Addressing these gaps, we developed a new real-time, label-free radiofrequency sensor for monitoring bacteria and biofilm growth. The sensor, an open-ended coaxial probe, offers enhanced monitoring of bacterial development stages. Tested on a biological model of bacteria and bacteriophages, our results indicate the limitations of traditional OD measurements, influenced by factors like sedimented cell fragments and biofilm formation on well walls. While confocal microscopy provides detailed 3D biofilm architecture, its real-time monitoring application is limited. Our novel approach using radio frequency measurements (300 MHz) overcomes these shortcomings. It facilitates a finer analysis of the dynamic interaction between bacterial populations and phages, detecting real-time subtle changes. This method reveals distinct phases and breakpoints in biofilm formation and virion interaction not captured by conventional techniques. This study underscores the sensor’s potential in detecting irregular viral activity and assessing the efficacy of anti-biofilm treatments, contributing significantly to the understanding of biofilm dynamics. This research is vital in developing effective monitoring tools, guiding therapeutic strategies, and combating AMR.

Silicone materials are widely used in fouling release coatings, but developing eco-friendly protection via biosourced coatings, such as polyhydroxyalcanoates (PHA) presents a major challenge. Anti-bioadhesion properties of medium chain length PHA and short chain length PHA films are studied and compared with a reference Polydimethylsiloxane coating. The results highlight the best capability of the soft and low-roughness PHA-mcl films to resist bacteria or diatoms adsorption as compared to neat PDMS and PHBHV coatings. These parameters are insufficient to explain all the results and other properties related to PHA crystallinity are discussed. Moreover, the addition of a low amount of PEG copolymers within the coatings, to create amphiphilic coatings, boosts their anti-adhesive properties. This work reveals the importance of the physical or chemical ambiguity of surfaces in their anti-adhesive effectiveness and highlights the potential of PHA-mcl film to resist the primary adhesion of microorganisms.

The polyhydroxyalkanoates (PHAs) are biobased, biocompatible and biodegradable polyesters. To enhance their biodegradability and flexibility, we develop low density PHAs by an emulsion-templated method without organic solvent. Polycaprolactone (PCL) and castor oil are required to improve the flexibility and to generate the porosity, respectively. To overcome the well-known lack of compatibility between PHA and PCL, pluronic is introduced to improve the miscibility of these polyesters The densities of native PHA and PCL are 1.2 g.cm−3 and the densities decreased to 0.49 g.cm−3 in presence of castor oil (40 wt%). Different PHAs were studied: polyhydroxybutyrate (PHB), polyhydroxybutyrate-co-hydroxyvalerate (PHBHV) and polyhydroxybutyrate-co-hydroxyhexanoate (PHBHHx). The porous PHBHHx based material showed the best colonization by Pseudomonas, followed by the PHBHV and PHB. This colonization only occurred in the surface and no bacterial diffusion was observed inside the material. The biodegradability study in presence of lipase showed that after 8 days, the weight losses are, respectively, 20% and 75% when the densities decreased from 0.82 g.cm−3 to 0.49 g.cm−3. These results showed the importance of the porosity on the biodegradation of PHAs.

Hydrogels based on poly(3-hydroxyalkanoate) (PHA) sulfonate and poly(ethylene glycol) diacrylate, PEGDA, are prepared. First, PHA sulfonate is synthesized from unsaturated PHA by a thiol-ene reaction in the presence of sodium-3-mercapto-1-ethanesulfonate. The hydrophilicity of PHAs is considerably increased by adding sulfonate functions, and three amphiphilic PHAs are synthesized, containing 10, 22, or 29% sulfonate functions. Then, hydrogels are formed in the presence of PEGDA having different molar masses, that is, 575 or 2000 g mol-1. The hydrogels show fibrillar and porous structures observed in cryo-MEB with pore sizes that vary according to the content of sulfonated groups (10 to 29 mol %) ranging from 50 to more than 150 nm. Furthermore, depending on the proportions of the two polymers, a variable rigidity is observed from 2 to 40 Pa. In fact, the evaluation of the dynamic mechanical properties of the hydrogel determined by DMA reveals that the less rigid hydrogels hinder the adhesion of Pseudomonas aeruginosa PaO1 bacteria. Finally, these hydrogels swelling up to 5000% are noncytotoxic, allowing the adhesion and amplification of immortalized C2C12 cells, and they are therefore seen as promising materials both for repelling PaO1 bacteria and for amplifying myogenic cells.

Due to environmental regulations, antifouling marine coatings must be gradually replaced by biocide-free coatings. Marine organisms weakly adhere to fouling release coatings, presenting a low surface free energy and a high elasticity, so they can be readily removed by the sheer force of water. Currently, these materials are mainly composed of petrochemical polymers, such as silicone or fluoropolymers, with hydrophilic polymers as additives. However, following the ever-increasing environmental concerns, the research on new, alternative, eco-friendly coatings is oriented towards the use of biobased polymers from renewable resources. Two main families have been studied: polyhydroxyalkanoates (PHAs) and polysaccharides. PHAs are produced by bacteria in stressful conditions, while polysaccharides are extracted from plants, animals, or micro-organisms such as bacteria, in which case they are called exopolysaccharides (EPS). Since the use of these polymers is a non-toxic approach to controlling fouling colonization, this review provides an overview of these biobased polymers for their applications in new anti-adhesive marine coatings.

Bacterial biofilms have a significant economic and health impact in many different domains. In such films, the extracellular matrix prevents the diffusion of biocides, so antibiotic treatments require a concentration 500 to 1000 times higher than that used to eliminate the same bacteria when present as planktonic stage. Early detection of biofilms is therefore essential for effective eradication. In this paper, we present the development of a real-time and label-free radiofrequency biosensor dedicated to the monitoring of bacteria and biofilm growth. Its principle relies on an open-ended coaxial probe sensitive to the variation of the electrical conductivity of the probed medium in the microwave range. As shown, between 0.3 and 1 GHz, the high sensitivity of the method (2.3 × 104 CFU/mL) highlights the biofilm growing at the early stage of its formation. To demonstrate experimentally such effects, two model bacteria, Vibrio natriegens and P. aeruginosa, are considered. The proposed method should therefore be considered as a promising technique for biofilm monitoring in batch bioreactors or flow cells experiments.

Biofilms, responsible for many serious drawbacks in the medical and marine environment, can grow on abiotic and biotic surfaces. Commercial anti-biofilm solutions, based on the use of biocides, are available but their use increases the risk of antibiotic resistance and environmental pollution in marine industries. There is an urgent need to work on the development of ecofriendly solutions, formulated without biocidal agents, that rely on the anti-adhesive physico-chemical properties of their materials. In this context, exopolysaccharides (EPSs) are natural biopolymers with complex properties than may be used as anti-adhesive agents. This study is focused on the effect of the EPS MO245, a hyaluronic acid-like polysaccharide, on the growth, adhesion, biofilm maturation, and dispersion of two pathogenic model strains, Pseudomonas aeruginosa sp. PaO1 and Vibrio harveyi DSM19623. Our results demonstrated that MO245 may limit biofilm formation, with a biofilm inhibition between 20 and 50%, without any biocidal activity. Since EPSs have no significant impact on the bacterial motility and quorum sensing factors, our results indicate that physico-chemical interactions between the bacteria and the surfaces are modified due to the presence of an adsorbed EPS layer acting as a non-adsorbing layer.

The development of biofouling is a major problem for marine industries. The conception of antifouling and fouling release coatings, with controlled physical-chemical properties is a promising strategy. Among them, amphiphilic systems, such as those composed of a hydrophobic polydimethylsiloxane matrix and a hydrophilic polyethyleneglycol additive are the most efficient and up to date. Despite their effectiveness, these systems are questioned due to the petrochemical origin of PDMS. The aim of this project was to substitute the PDMS matrix with a biopolymer, poly(3-hydroxybuyrate-co-3-hydroxyvalerate) and to improve its anti-adhesion properties through the elaboration of an amphiphilic system, via the addition of PEG or PHBHHx-b-PEG copolymer. The results, including the physico-chemical properties of PHBHV based coatings and static adhesion tests on a marine bacterium, Bacillus 4J6 and a diatom, Phaeodactylum tricornutum are compared with those of PDMS and PEG-modified PDMS coatings. Real antiadhesion activity was obtained for the PHBHV/PHBHHx-b-PEG system for a promising eco-friendly strategy.

The purpose of this study was to examine the impact of hydrophobicity, surface chemistry and topography on bacterial and microalgal adhesion. To this end, the effects of surface plasma treatments (argon (Ar) and tetrafluorocarbon (CF4)) of polycarbonate substrates on bioadhesion were investigated in vitro. Surfaces were characterized by goniometry, atomic force microscopy and X-ray photoelectron spectroscopy. Two marine bacterial strains, a hydrophobic Pseudoalteromonas sp. 5M6 and a hydrophilic Paracoccus sp. 4M6, and two microalgae (Cylindrotheca closterium and Porphyridium purpureum) involved in marine biofouling were selected. Their adhesion onto the substrates was observed and quantified using confocal laser scanning microscopy–microfluidic flow cells. It was demonstrated that the combination of three parameters – namely, surface energy, fluorination and nanotopography – significantly decreases the adhesion of three microorganisms out of four (Pseudoalteromonas sp. 5M6, C. closterium and P. purpureum), whereas one parameter on its own is insufficient.

Biofouling is a phenomenon affecting all the infrastructures immerged in marine and freshwater environments. This colonization leads to a deterioration of the surfaces implied and affects the performances of the different structures as the decrease of ship speed or the increase of fuel consumption. Polemics around harmful antifouling coatings being more and more concerning, an alternative to toxic compounds is here proposed. The effect of three different zeolites, pure or copper loaded, is evaluated on two fouling diatoms, Cylindrotheca closterium and Amphora sp. These organisms display different sensitivities to copper usually used in antifouling paint. Finally, it has been shown that pure zeolites had stimulating effect on microalgae growth while copper loaded ones seemed efficient to inhibit their development. However, natural zeolite appeared less effective than the two synthetic after 7 days incubation. These differences seemed to be due to the bonds created by copper in the materials and to the leaching of metallic ions. Finally, the constant release of active agent in the medium by the minerals appeared to be the key for an interesting application in antifouling systems.

Fouling release coatings are known to be ecofriendly and to be a good alternative to the coatings containing biocides. To improve their efficiency and lifespan the incorporation of additives seems required. Amphiphilic system as PEG-silicone coatings have a lower impact on the environment. However, PEG oxidation in seawater impacts its lifespan. In this context, the development and incorporation of new hydrophilic additives offers great potentiel. The objective of this study is to design an amphiphilic fouling release coating containing poly(oxazoline) (POx) as additives. POx have similar physical properties as PEG and have already been used in biomedical applications. POx with a trimethoxysilane end-group has been synthesized to be crosslinked in a RTV silicone coating. The impact of its incorporation in a PDMS coating has been evaluated on surface properties and on coating organization. The results have been compared with a similar PEG-silicone coating. In addition, microbiologic assays have been carried out to evaluate the bacterial adhesion and the fouling properties of the coating. Two biomedicals bacteria and a marine bacterium were used to confirm the interest of POx. POx-silicone coating showed similar fouling efficiency against bacteria as PEG-silicone coating despite a bigger surface roughness and a lower compatibility with PDMS.

Microorganisms able to form biofilms in marine ecosystems are selected depending on immersed surfaces and environmental conditions. Cell attachment directly on toxic surfaces like antifouling coatings suggests a selection of tolerant (or resistant) organisms with characteristics conferring adaptive advantages. We investigated if environment would drive metal resistance gene abundance in biofilms on artificial surfaces. Biofilms were sampled from three surfaces (a PVC reference and two antifouling coatings) deployed in three coastal waters with dissimilar characteristics: The Mediterranean Sea (Toulon) and Atlantic (Lorient) and Indian (Reunion) Oceans. The two coatings differed in metals composition, either Cu thiocyanate and Zn pyrithione (A3) or Cu2O (Hy). Metal resistance genes (MRG) specific to copper (cusA, copA, cueO) or other metals (czcA and pbrT) were monitored with qPCR in parallel to the microbial community using 16S rRNA gene metabarcoding. A lower α-diversity on A3 or Hy than on PVC was observed independent on the site. Weighted Unifrac suggested segregation of communities primarily by surface, with lower site effect. Metacoder log2 fold change ratio and LeFSe discrimination suggested Marinobacter to be specific of Hy and Altererythrobacter, Erythrobacter and Sphingorhabdus of A3. Likewise, the relative abundance of MRG (MRG/bacterial 16S rRNA) varied between surfaces and sites. A3 presented the greatest relative abundances for cusA, cueO and czcA. The latter could only be amplified from A3 communities, except at Toulon. Hy surface presented the highest relative abundance for copA, specifically at Lorient. These relative abundances were correlated with LeFSe discriminant taxa. Dasania correlated positively with all MRG except cueO. Marinobacter found in greater abundance in Hy biofilm communities correlated with the highest abundances of copA and Roseovarius with czcA. These results prove the selection of specific communities with abilities to tolerate metallic biocides forming biofilms over antifouling surfaces, and the secondary but significant influence of local environmental factors.

Lorsqu’une surface est immergee, un phenomene de « fouling » apparait : une colonisation spontanee par des microorganismes a lieu. Les consequences de son developpement sur les surfaces immergees sont catastrophiques. Pour y remedier, des peintures dites « antifouling » sont utilisees depuis le debut du XX e siecle. Cet article presente les differentes strategies utilisees en 2020. Les deux premieres sections sont consacrees aux deux principaux mecanismes utilises : les revetements a liberation de biocides et les revetements a effet de surface. Les deux dernieres sections portent sur les nouvelles strategies developpees pour limiter l’impact sur l’environnement : les revetements hybrides et revetements topographies.