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Microbial biofilms are an extremely successful way of life. Bacteria and fungi benefit in this symbiotic life form of metabolic exchange, protection and genetic flexibility. They produce a matrix of organic molecules in which they are embedded and which offers new habitats to other organisms, such as other bacteria or fungi. Biofilms cannot be avoided to colonize surfaces in unsterile habitats. So, they can be found everywhere in nature and in technical systems, but they play an ambivalent role. On the one hand biofilms are essential to degrade and transform water contaminations, but on the other hand they can diminish product qualities and damage capital equipment. Biofilms can cover medical equipment such as catheters and pathogenic bacteria, which may be living in the biofilms, are a continuous source of infection of the patients. In addition, the metabolism of the biofilm microorganisms may change the composition of the fluids or contaminate them with their products. As biofilms are all-round, the understanding of the biofilm formation and its manipulation are of prime importance in microbiology and material sciences. The choice of a material and the corresponding surface properties like mechanical properties, structure, polarity, and chemistry influence the binding of various molecules and cells. The surface properties affect the biocompatibility of a material and consequently also bacterial adhesion, and biofilm growth. In this project hydrophobins are used as a novel modification of surfaces to change surface properties like hydrophobicity and thus might have an effect on biofilm formation. Hydrophobins are fungal proteins, which selfassemble on hydrophobic as well as hydrophilic surfaces into extremely stable monolayers. Recombinant hydrophobins provide the opportunity to use these highly surface-active proteins for large-scale surface coatings. Hydrophobins are non-toxic and can be used for surface modification and functionalization (with e.g. enzymes) of industrial relevant materials like steel, plastics, and ceramics. In this project hydrophobin coated surfaces and their properties are studied with respect to bacterial cell adhesion, cell differentiation, and cellular growth with the aim to influence biofilm formation. In the first part of the project recombinant hydrophobins were produced and purified. Different surfaces were coated with hydrophobins and characterized, since the coating efficiency is the basis for subsequent biofilm formation studies. Biofilms were grown on natural as well as hydrophobin coated surfaces and different methods were established to analyse biofilm formation. Since the hydrophobin coated surfaces did not reduce microbial growth, we designed modified fusion hydrophobins and attached cationic antimicrobial peptides (AMPs) to the hydrophobins.

International audience; Patterns of biofilm formation from a bare substratum were investigated in two streams from different bioclimatic regions: a Central-European (the Walzbach, SW Germany) and a Mediterranean (the Fuirosos, NE Spain). Algal biomass, diatom community structure and Extracellular Polymeric Substances (EPS) were analyzed during a 60-day colonization period. There was a faster colonization of algae in the Mediterranean stream and a slower and gradual colonization in the Central-European stream. The successional patterns of diatom communities in the Mediterranean stream were altered by flood episodes that were followed by re-colonization episodes (days 14 and 44). Biofilms in this stream had a higher amount of early colonizing diatom species (Ulnaria ulna and Karayevia clevei) and polysaccharide development in the EPS matrix. Differences might be an adaptation to the hydrological changes. The Central European biofilms showed a gradual increase in microbial community complexity, reflecting the higher hydrological stability as well as higher nutrient availability. While the colonization dynamics in the Mediterranean stream reflects hydrological alterations, the succession in the Central European stream is mostly autogenic and results of the biological interactions in the biofilm.

Research on implant infections requires cooperative efforts and integration between basic and clinical expertises. An international group of women scientists is acting together in this field. The main research topics of the participants of this group are described. Formation of bacterial biofilms, antibiotic resistance and production of virulence factors like adhesins and toxins are investigated. New biomaterials, coatings and drugs designed to inhibit microbial adhesion are evaluated, and infection-resistant biomaterials are under study, such as a novel heparinizable polycarbonate-urethane (Bionate) or incorporation of diamino-diamide-diol (PIME) to reduce bacterial attachment. The correlation between biofilm production and the accessory-gene-regulator (agr) is investigated in Staphylococcus aureus. The ability to form biofilm has also been shown to be one of the important virulence factors of Enterococcus faecalis, favouring colonization of inert and biological surfaces. The study of quorum sensing has led to the discovery of a quorum sensing inhibitor termed RIP that suppresses staphylococcal biofilm and infections. The immune response and the local defence mechanisms of the host against implant-associated infections, activation and infiltration of immunocompetent cells into the sites of infection have been studied in patients with implant-associated osteomyelitis. Production of monoclonal antibodies (mAbs) as possible vaccines against the staphylococcal collagen-binding MSCRAMMs is in progress.

International audience; Cette étude vise à comparer les processus de colonisation par le biofilm dans deux cours d'eau de régimes hydrologiques différents : l'un intermittent (Fuirosos, région méditerranéenne), le second permanent (Walzbach, Europe centrale). Les patrons observés des populations microbiennes et algales coïncident avec les événements de crue à Fuirosos, tandis que la succession temporelle est plus graduelle à Walzbach. Les activités enzymatiques extracellulaires (concentrations en EPS plus élevées à Fuirosos) traduisent également la réponse fonctionnelle des biofilms au régime fluctuant de Fuirosos, afin d'éviter le détachement lié aux crues fréquentes.