Antifouling properties of amphiphilic poly(3-hydroxyalkanoate): an environmentally-friendly coating.

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.

Alteration of bacterial adhesion induced by the substrate stiffness.

The aim of this paper is to study the impact of the substrate stiffness on the bacterial adhesion. For this purpose, agarose hydrogels are used as substrates with controlled mechanical properties. Indeed, the elastic modulus of these hydrogels, more precisely the shear storage moduli G', evolves with the agarose concentration (in this study from 0.75% to 3%). Other physico-chemical characteristics of the surface, known to be involved in bacterial adhesion, as hydrophobicity, were confirmed to remain constant. Two marine bacterial strains, a positive Gram Bacillus sp. 4J6 and a negative Gram Pseudoalteromonas sp. D41 were selected. Their retention on the substrates was analysed by confocal laser scanning microscopy and by counting of viable adhered bacteria. It was demonstrated that surface elastic modulus correlated with bacterial retention. Bacteria D41 adhered in higher numbers to rigid surfaces. For 4J6, bacterial adhesion patterns were changed: clusterings were observed on surfaces with lower elastic modulus. Furthermore, a proteomic study, based on the total soluble proteome of D41 strain, highlights an impact of elastic modulus on proteins synthesis. These data demonstrated an adapted response of adhering bacteria on hydrogels of varying mechanical properties.

Monitoring of microbial adhesion and biofilm growth using electrochemical impedancemetry.

Electrochemical impedance spectroscopy was tested to monitor the cell attachment and the biofilm proliferation in order to identify characteristic events induced on the metal surface by Gram-negative (Pseudomonas aeruginosa PAO1) and Gram-positive (Bacillus subtilis) bacteria strains. Electrochemical impedance spectra of AISI 304 electrodes during cell attachment and initial biofilm growth for both strains were obtained. It can be observed that the resistance increases gradually with the culture time and decreases with the biofilm detachment. So, the applicability of electric cell-substrate impedance sensing (ECIS) for studying the attachment and spreading of cells on a metal surface has been demonstrated. The biofilm formation was also characterized by the use of scanning electron microscopy and confocal laser scanning microscopy and COMSTAT image analysis. The electrochemical results roughly agree with the microscope image observations. The ECIS technique used in this study was used for continuous real-time monitoring of the initial bacterial adhesion and the biofilm growth. It provides a simple and non-expensive electrochemical method for in vitro assessment of the presence of biofilms on metal surfaces.