Francisella tularensis is a highly virulent zoonotic pathogen that is the causative agent of tularemia in humans. Two subspecies of F. tularensis are the most virulent in humans: tularensis (type A) and holarctica (type B), with less than 10 organisms via aerosol of a type A strain having the ability to cause fatal infection. Over the last decade much research has been done on the pathogenesis of this unique intracellular bacterium and many different virulence factors have been identified. The goal of this dissertation has been to identify and characterize the capsule-like complex (CLC) surface antigen of F. tularensis, and to determine its role in virulence and immunoprotection in a mouse model. In addition, I have investigated the role of CLC in biofilm formation. The CLC appears as a negatively staining material surrounding F. tularensis cells during transmission electron microscopy (TEM). I found that the CLC in the type B live vaccine strain (LVS) could be significantly diminished by deleting two glycosyl transferase genes (LVSΔ1423-22) in the putative polysaccharide locus, FTL_1432-FTL_1421. In addition, I determined that the CLC was not a typical polysaccharide capsule, but was in fact composed of over 50 proteins and glycoproteins including known virulence determinants, such as GroEL, DnaK, and ClpB. Upon further evaluation of the CLC, I determined that it was composed of an increase in production of outer membrane vesicles and tubules (OMV/T). These OMV/T appeared to be self-aggregating into what I visualized through TEM as the CLC. LVSΔ1423-22 was attenuated in the mouse model, and BALB/c mice immunized with CLC and adjuvant were protected against challenge with LVS. In addition to virulence, the CLC appears to play a role in biofilm formation and development. F. tularensis type B strains lacking the surface antigens CLC or CLC and O-antigen, develop a 2-7-fold more robust biofilm than the parent strains. The biofilm matrix contains a glucan-like EPS, proteins, and extracellular DNA, and further characterization may lead to determining if the biofilm acts as an environmental survival mechanism for F. tularensis. In summary, the CLC appears to be a novel surface antigen composed of upregulated OMV/T that is present in type A and B F. tularensis. Deficiency in CLC contributes to increased biofilm formation that could contribute to the survival of F. tularensis in a wide range of environmental niches. Furthermore, the CLC contributes to virulence of type B strains and elicits a protective immune response to type B challenge. A CLC-deficient type A strain could be a candidate for a new live vaccine strain, and therefore further investigation of such a mutant is warranted. / Ph. D.

Yes / Bacterial quorum sensing has been implicated in a number of pathogenic bacterial processes, such as biofilm formation, making it a crucial target for developing materials with a novel antibiotic mode of action. This paper describes poly(N-isopropyl acrylamide) that has been covalently linked, at multiple chain ends, to homoserine lactone to give a highly branched polymer functionalized with a key messenger molecule implicated in QS. This novel functional material has shown promising anti-QS activity in a Chromobacterium violaceum assay.

Klebsiella pneumoniae is a Gram-negative bacterium commonly giving rise to nosocomial infections especially in immunocompromised individuals. The high occurrence of antibiotic resistant K. pneumoniae strains in combination with the bacterium’s ability to form biofilms that are naturally more tolerant to antibiotic treatment represents a burden for the healthcare system due to potential therapeutic failure. In this study, we were investigating the effect of gentamicin, cefotaxime and ciprofloxacin on biofilm formation and eradication of a multi-resistant ESBL-producing K. pneumoniae strain associated with an outbreak at the Uppsala University Hospital in Uppsala, Sweden, from 2005 to 2007. Multidrug resistance was encoded on the pUUH239.2 plasmid. We also studied how resistant bacteria are selected for in mixed biofilm populations consisting of both resistant and susceptible bacteria under antibiotic treatment. Biofilms were grown in vitro by using an in-the-lab developed peg model. Biofilms were either allowed to form in the presence of the antibiotics or pre- formed and then exposed to antibiotic treatment at different time points. Our results suggest that gentamicin, cefotaxime and ciprofloxacin inhibit biofilm formation at concentrations below the minimum inhibitory concentration (MIC) and that biofilms become more tolerant to antibiotic treatment with increasing maturation. We further observed that increasing antibiotic concentrations select for the presence of the plasmid in less mature biofilms. Overall, these findings highlight the need of early antibiotic treatment during infection and give insight into the dynamics of resistant and susceptible bacteria in mixed biofilm populations in the presence of antibiotics.

In this study, a well biofilm-forming bacterial strain was isolated from oil contaminated water and sediment samples collected in petroleum storage Duc Giang, Hanoi. It was identified as Paracoccus sp. DG25 and registered in the GenBank database with the accession numbers KJ608354. Several biophysical and bio-chemical conditions for the biofilm formation of the strain were estimated such as pH, temperature, carbon sources and nitrogen sources. As the results the biofilm forming capacity was highest at pH 7, 37 oC, on maltose and supplemented with KNO3. Using these optimal conditions, the formed biofilm degraded 76.07 % of pyrene after 7 day-incubation, with the initial concentration of 300 ppm by high-performance liquid chromatography (HPLC) analysis. To our knowledge, there is rare publication on pyrene degradation by biofilm-forming bacteria. Therefore, the obtained results show that biofilm formed the strain Paracoccus sp. DG25 may considerably increase the degrading efficiency of pyrene and may lead to a new approach to treat polycyclic aromatic hydrocarbons containing in petroleum oil contaminated water in Vietnam. / Trong nghiên cứu này, từ các mẫu đất và nước nhiễm dầu lấy tại kho xăng Đức Giang, Hà Nội, chúng tôi đã phân lập được chủng vi khuẩn có khả năng tạo màng sinh học tốt. Chủng vi khuẩn này đã được phân loại và định tên là Paracoccus sp. DG25 với số đăng ký trên ngân hàng Gen là KJ608354. Chúng tôi cũng đã nghiên cứu một số điều kiện hóa lý ảnh hưởng tới khả năng hình thành màng sinh học như pH, nhiệt độ, nguồn Carbon và nguồn Nitơ. Kết quả cho thấy, chủng DG25 có khả năng tạo màng tốt nhất ở các điều kiện pH 7, 37 oC, nguồn Carbon là maltose và nguồn Nitơ là KNO3. Sử dụng các điều kiện tối ưu này để tạo màng và đánh giá khả năng phân hủy pyrene của màng tạo thành. Bằng phương pháp sắc ký lỏng cao áp, chúng tôi đã đánh giá được hàm lượng pyrene bị phân hủy sau 7 ngày nuôi tĩnh bởi màng sinh học của chủng DG25 lên tới 76,07 % với nồng độ ban đầu là 300 ppm. Cho tới nay, chưa có nhiều công bố về hiệu quả phân hủy pyrene của các chủng vi khuẩn tạo màng sinh học. Do vậy, kết quả đạt được này mở ra khả năng sử dụng màng tạo thành bởi chủng DG25 để nâng cao hiệu quả phân hủy pyren và có thể mở ra phương pháp mới nhằm xử lý các hợp chất hydrocarbon thơm có trong nước ô nhiễm dầu ở Việt Nam.

Investigations were carried out to assess biofilm formation within a model warm water distribution system (test rig) under a variety of conditions. Analysis methods included ATP-/ culture-based analysis, SEM and confocal microscopy. Molecular-based community analysis was carried out using PCR/DGGE. High pH (9.53-10.08), induced by the presence of a sacrificial anode within the water heater, had a profound inhibitive effect on the culturability of biofilm bacteria on copper (Cu) pipe within the test rig. Concurrent investigations into the effect of stagnation (varied periods of non-flushing) appeared to contradict the widely held view that stagnation is conducive to biofilm formation, with greater flushing frequencies resulting in increased biofilm. It was concluded that a higher frequency of nutrient-delivering events were largely responsible for this and that in systems where lengthier stagnation periods were employed, factors such as low oxygen and reduced nutrient levels inhibited biofilm formation on previously uncontaminated Cu pipe. Thermal purging (TP) over a 28 day period of 30 second, 12 hourly flushing at 41 °C and three-daily one minute purging with 70 °C water resulted in a 99% reduction in the culturability of biofilm bacteria on both Cu and LLDPE. However, confocal microscopical analysis of bacterial numbers indicated that 25.06% (Cu) and 21.55% (LLDPE) of the initial bacterial population remained viable. A large proportion of non-viable biofilm bacteria were also observed. Further work is therefore required in order to optimize TP within the test rig. Biofilm formation on a range of different materials; Cu, stainless steel, PEX, and EPDM, showed significantly greater biofilm development on EPDM in comparison to the other materials. Preliminary investigations of LLDPE and tap outlet fittings showed that laminar flow outlet fittings may act as reservoirs for the development and subsequent dissemination of biofilm. Molecular bacterial community structural studies of test rig biofilms clearly showed that biofilm community composition was significantly affected by both temporal and environmental factors, and varied at points within the same system. Sequencing did not provide a great insight into the composition of the bacterial communities within the test rig, and further work is required to gain a more complete picture of bacterial community diversity within the test rig. These studies show that biofilm formation within the test rig is greatly influenced by a wide variety of factors. The test rig’s unique design necessitates a cautionary approach when making comparisons with, for example, larger water distribution systems

La contamination des milieux aquatiques urbains se caractérise aujourd'hui par un mélange de micropolluants d'origines et de types variés. Les conséquences de ce type de contamination, multiples mais faibles et chroniques, sur les écosystèmes aquatiques sont difficiles à évaluer. En effet, il est difficile d'une part de dresser un état des lieux précis de la contamination et d'autre part, de relier cette contamination à la réponse biologique des organismes exposés puisqu'elle n'engendre pas nécessairement des effets visibles et immédiats. Cette étude a pour objectif de développer une méthodologie permettant d'utiliser le périphyton pour évaluer l'impact d'une contamination urbaine typique. Les biofilms sont des communautés aquatiques complexes jouant un rôle primordial dans le fonctionnement des écosystèmes aquatiques. Leur réponse biologique à une perturbation peut s'évaluer au niveau structurel comme au niveau fonctionnel. Une première étape de ce travail a consisté à développer d'une part un test de toxicité aiguë permettant d'évaluer la tolérance de la composante hétérotrophe des biofilms selon le concept PICT, et d'autre part l'utilisation de la technique d'empreinte génétique ARISA pour évaluer des modifications de structure des communautés bactériennes et eucaryotes des biofilms. Les méthodologies développées ont ensuite été testées au laboratoire par des expositions de périphyton à des métaux à des concentrations environnementales. Par la suite, elles ont pu être déployées in situ : d'abord dans un gradient de contamination multi-métallique sur la Seine avec des prélèvements ponctuels de biofilms naturels ainsi qu'une expérience de transposition (amont/aval de l'agglomération parisienne). Enfin, le lien entre la tolérance du périphyton et la contamination métallique globale du milieu a été exploré à l'échelle d'un bassin versant. Les résultats sont prometteurs quant à l'utilisation du périphyton pour évaluer l'impact d'une contamination urbaine / Urban aquatic ecosystems are these days contaminated by mixtures of micropollutants of diverse types and origins. Such contaminations, which are multiple, chronic and non-lethal, raise increasing concern among the scientific community. Indeed, a precise evaluation of exposure levels is difficult to obtain. Moreover, establishing a causal link between contamination and the induced biological response of aquatic organisms is complex as no direct and visible effects can be observed. The aim of this study is to develop a methodology for the use of periphyton as a biomarker of urban pollution. Biofilms are complex aquatic communities and play an important role in aquatic ecosystems. Their response to a disruption can be assessed both in terms of structure or functional modifications. Our first step was to develop both a PICT approach with a new short-term toxicity test to measure the tolerance to metal of the heterotrophic component of biofilms and the use of a fingerprinting technique (ARISA) to reveal structure modifications of both bacterial and eukaryotic communities. The methodologies thus developed were tested in a microcosm study by exposing periphyton to metals at environmental levels. They were then used in field studies: first in a multi-metallic gradient along the Seine river by punctual sampling of natural periphyton and also in a translocation study (upstream/downstream the Paris urban area). Furthermore, the link between biofilm tolerance levels and the global metallic contamination was explored at the watershed scale. It is hoped that the future use of this approach will help to understand the impacts of human activities, especially toxic pressure, on aquatic ecosystems

Les biofilms sont des édifices macromoléculaires qui résultent de l'adhérence de microorganismes à une surface. Ils sont constitués de cellules enchâssées dans un réseau d'exopolymères d'origine biologique qui forment une matrice extracellulaire. Les biofilms posent des problèmes technologiques et sanitaires dans de nombreux domaines, aussi bien agroalimentaire, médical, ou industriel. Comprendre les mécanismes de formation de ces structures est donc un enjeu majeur. Malgré une grande diversité de la structure des biofilms, de grands principes semblent en régir la composition. Ainsi, la présence de polysaccharides comme l'alginate et la cellulose joue un rôle majeur dans leur formation et dans la définition de leurs propriétés mécaniques. Si la présence de polymères protéiques comme les fibres amyloïdes semble avoir un caractère universel au sein des biofilms, leur rôle dans la formation de la matrice et dans ses propriétés mécaniques restait à définir. Lors de cette étude, nous avons caractérisé la structure et la composition de trois biofilms monobactériens issus de trois espèces différentes P. aeruginosa NK 125502, S. enterica CIP 58.58 et S. epidermidis CIP 53.124. Nous avons décrit la formation de fibres amyloïdes par différents peptides issus de protéines bactériennes impliquées dans la formation de biofilm et montré par différentes techniques qu'ils sont capables de former des fibres amyloïdes. Nous avons notamment identifié un peptide amyloïde, suggérant la présence de ce type de fibre au sein des biofilms de Staphylococcus, mais aussi plus généralement dans les biofilms des espèces exprimant une protéine de type Bap (Biofilm associated protein). Enfin, nous avons analysé les propriétés mécaniques de différentes matrices synthétiques à base d'alginate et de méthyl-cellulose, en présence et en absence de protéines et de peptides amyloïdes afin de mieux comprendre l'apport qu'a ce type de fibre sur les propriétés de ces structures. Ainsi, les fibres amyloïdes modifient les propriétés mécaniques des gels synthétiques, permettant d'augmenter la déformation sous contrainte. En conclusion, ce travail apporte de nouveaux éléments pour la compréhension du rôle des fibres amyloïdes dans le renforcement de la matrice du biofilm. La capacité à former des fibres amyloïdes par un peptide issu de la protéine Bap de S. epidermidis suggère que cette propriété est plus largement présente au sein de cette famille de protéines. Les travaux menés au cours de cette thèse, et l'ensemble des techniques utilisées, avec notamment la mise au point de l'observation de la biréfringence du rouge Congo par microscopie confocale permettront de développer les études sur cette famille de protéines amyloïdes ainsi que sur les matrices complexes de type biofilm / Biofilms are macromolecular structures which result from the adhesion of microorganisms to a surface. They consist of cells embedded in a network of exopolymers of biological origin which form an extracellular matrix. Biofilms pose technological and health problems in many industrial and medical domains. Understanding the mechanisms of formation of these structures is a major challenge. Despite a great diversity in the structure of biofilms, universal principles seem to govern their composition. Thus, the presence of polysaccharides such as alginate and cellulose plays a major role in their formation and in determining their mechanical properties. If the presence of protein polymers such as amyloid fibers seems to be universal within biofilms, their role in the formation and in the mechanical properties of the matrix remains to be defined. In this study, we characterized the structure and composition of monobacterial biofilms from three different species: P. aeruginosa NK 125502, S. enterica CIP 58.58 and S. epidermidis CIP 53124. We described the formation of amyloid fibers by different peptides from proteins involved in bacterial biofilm formation. Morover our results suggest the presence of this type of fiber within biofilms of Staphylococcus, but also more generally in biofilms of bacteria expressing a protein of the Bap family (Biofilm associated protein). Finally, we analyzed the mechanical properties of various synthetic matrices made of alginate and methyl-cellulose in the presence and absence of protein and amyloid peptides in order to better understand the contribution of this type of fiber on the properties of these matrices. Hence, amyloid fibers modify the mechanical properties of synthetic gels, by increasing the deformation under stress.In conclusion, this study provides new evidence for understanding the role of amyloïd fibers in the biofilm matrix strengthening. The formation of amyloid fibers by the Bap protein of S. epidermidis suggests the possibility of a general amyloid behavior in the Bap protein family. A new application of confocal laser scanning microscopy was developped: the use of the confocal microscope to image the birefringence of Congo red.

La plaie tumorale est une infiltration par des cellules tumorales du tissu cutané, des vaisseaux sanguins et/ou lymphatiques. Ces plaies peuvent se présenter sous des aspects très différents accompagnés de symptômes variés. Outre les risques d'infection locale, les odeurs nauséabondes posent des problèmes récurrents d'isolement social, de difficultés conjugales et entrainent une sensation de dégout, de pourriture, voire de mort imminente. Elles influencent même le comportement médical. La colonisation bactérienne, les odeurs et les risques infectieux semblent intimement liés chez ces patients porteurs de plaie, dont l'immunité est le plus souvent affaiblie par l'administration de traitements anticancéreux. Ce projet a consisté à : 1) créer un fichier dynamique de données et prélever les patients porteurs de plaies tumorales, dans le cadre d'un travail de recherche clinique, 2) par une approche expérimentale personnelle et collaborative: caractériser la flore microbienne, la présence éventuelle de biofilm et les composés volatils des plaies, 3) analyser l'ensemble des données en mettant en évidence, si elles existent, les corrélations entre résultats des prélèvements et observations cliniques, 4) proposer de premières hypothèses, des pistes de solution, une adaptation des pratiques de soins.Une flore mixte composée de 54 bactéries différentes a été retrouvée sur les plaies et la présence de biofilm mise en évidence dans 35% des cas. 91 composés volatils ont été identifiés. Aucune infection n'a été relevée durant la période d'évaluation. Les conséquences de l'interactivité entre les bactéries, le biofilm et les composés volatils nous amènent à penser qu'il serait nécessaire de: 1) développer de nouvelles stratégies et topiques, 2) poursuivre les travaux sur le biofilm, 3) construire des projets en liens avec des psycho-oncologues et neuropsychiatres, 4) progresser vers la conception d'outils diagnostics et l'identification de biomarqueurs. / The malignant wound is an infiltration by tumoral cells of the cutaneous tissue, the blood and/or lymphatic vessels. These wounds can appear in different forms and and be accompagnied by various symptoms. Independently of the septic risk, the presence of nauseating odors induces social, family and conjugal difficulties, expressed mostly by disgust, a sensation of dirt or decay. It influences the medical behavior.Bacterial colonisation, odors and septic risks seem to be connected and mainly occur in patients who have a chronic wound and are immunodepressed by the anticancer therapies. This projetc [was] consisted in: 1) create a case report form and sample the malignant wound (clinical research), 2) characterize the microbial flora, the biofilm, and the volatile compounds with an experimental and collaborative approach, 3) analyse the results and the potential correlation between [the] laboratory's results and the clinical aspect of the wound, 4), propose potential solutions, hypothetis, and improvements of the clinical practice.A mixed flora, composed of 54 different bacterial types was identified; a biofilm was caracterized in 35% of cases. 91 volatile compounds were identified. No infection occurred during the evaluation period. The consequences of the interactivity of the bacteria, the biofilm and the volatils compounds suggest to: 1) develop new strategies and topics, 2) continue the research on the biofilm, 3) propose a research program with psycho-oncologists and neuropsychiatrics, 4) progress toward diagnostic tests conception and biomarkers identification.

Les géomembranes (GMB) en polyéthylène haute densité (PEHD) sont utilisées comme barrière d'étanchéité dans les installations de stockage de déchets non dangereux (ISDND). Malgré les bonnes propriétés initiales du PEHD, face aux agressions chimiques et biologiques d'un lixiviat de déchets et aux contraintes thermiques et mécaniques générées par le massif de déchets, sa durabilité reste une question ouverte. L'objectif de cette thèse est de contribuer au développement d'un modèle cinétique non empirique de prédiction de la durée de vie des GMB en PEHD, qui prend simultanément en compte les effets du vieillissement chimique et biologique. Pour cela, nous cherchons à déterminer d'une part les paramètres d'extraction des antioxydants constitutifs des GMB, première étape du vieillissement des GMB, et d'autre part les paramètres cinétiques de vieillissement oxydatif des PE, deuxième étape de vieillissement. Ceci nécessite de connaître et de comprendre les mécanismes physico-chimiques impliqués dans le vieillissement des PE dans les conditions particulières des ISDND. A partir d'une approche multi-échelle (macro- micro) et à l'aide de différentes techniques (IRTF, GPC HT, AED, essais de traction,…), nous évaluons l'impact du vieillissement accéléré sur la composition chimique, les structures macromoléculaire et cristalline ainsi que les propriétés d'usage des GMB et des films en PEHD. Cette étude a permis de déterminer un critère de fin de vie pertinent pour évaluer la durée de vie de la GMB : la fragilisation qui correspond à une masse molaire critique M'C d'environ 100 kg.mol-1. Un couplage de la modélisation chimique de la dégradation oxydante du polymère et biologique de la cinétique de croissance du biofilm est proposé. Enfin, dans une dernière partie, la même approche multi-échelle a été utilisée pour caractériser la dégradation de GMB vieillies 18 ans en bassin de stockage d'eau pour ainsi déterminer les mécanismes impliqués dans le vieillissement sur site / High Density PolyEthylene (HDPE) geomembranes (GMB) are used as basal liners in municipal solid waste (MSW) landfills. In spite of the good initial properties of the HDPE, his durability remains poorly known face to the chemical and biological strains of the MSW landfill leachate and the thermal and mechanical strains generated by the solid waste. The objective of this thesis is to contribute to the development of a non-empirical kinetic model for predicting HDPE GMB life cycle, that simultaneously takes into accounts the chemical and biological aging effects. For this purpose, we seek to determine on the one hand the extraction process parameters of the antioxidants present in the GMB, first step of the GMB aging, and on the other hand the kinetic parameters of the PE thermo-oxidation, second step of the GMB aging. This requires knowing and understanding the physico-chemical mechanisms involved in the PE aging in the particular conditions of MSW landfills. Using a multi-scale methodology (macro-micro) and multi-technique approach (FTIR; GPC-HT, DSC, tensile tests, …), we assess the impact of the accelerated aging on the chemical composition, on the macromolecular and crystalline structures and on the used properties of HDPE GMB and films. This study identified a relevant endlife criterion for assessing the GMB service lifetime: the embrittlement which corresponds to a critical molecular mass M'C of about 100 kg.mol-1. Coupling chemical oxidative degradation modelling of the polymer and biofilm growth kinetic modelling is proposed. In the last part, the same type of multi-scale approach has been applied to characterize the degradation of HDPE GMB aged 18 years in water storage basin in order to determine the mechanisms involved in natural aging

Le nickel est connu pour son utilisation dans la préparation d’alliages réputés peu sensibles à la contamination bactérienne, très utilisés dans les secteurs agro-alimentaires et médicaux. Cependant, les bactéries apparaissent capables d’adhérer même à ce type de matériau et de le coloniser sous forme de biofilms. Les biofilms sont des communautés de micro-organismes, adhérant entre eux et à une surface, grâce à la sécrétion d’une matrice adhésive offrant une protection contre la dessiccation, les défenses de l’hôte et un grand nombre d’agents antimicrobiens. Ces biofilms manifestent des propriétés de multirésistances aux biocides qui causent des problèmes sanitaires majeurs dans les installations hospitalières et industrielles. D’importantes modifications de l’expression génétique accompagnent la vie en biofilm et induisent des caractères spécifiques dont des résistances accrues aux biocides et la production de facteurs de virulence. Parmi ces derniers, les curli, qui sont un composé protéique majeur de la matrice extracellulaire chez les bactéries Escherichia coli et Salmonella spp., jouent un rôle clé dans la formation de biofilms sur surfaces inertes et biologiques. Ce travail a consisté à explorer la contribution de la vie en biofilm à la survie des bactéries Escherichia coli K-12 productrices de curli en présence de nickel. Pour cela, l’effet physiologique d’ions solubles de nickel sur la survie des bactéries a été testé sur des supports inertes en polystyrène ou en acier. Nous avons montré que des concentrations sub-inhibitrices de nickel induisent une augmentation de l’épaisseur et de la densité du biofilm. Cet effet ne dépend pas des modifications physico-chimiques de la surface cellulaire par le nickel, ni de l’activité de la seule pompe d’efflux à nickel connue d’E. coli, RcnA. Par contre, le nickel à faible concentration induit l’expression des curli, ainsi que leur production. C’est donc via l’activation transcriptionnelle des gènes codant les curli que l’augmentation du biofilm par le nickel se produit. Ce travail s’est également appliqué à rechercher la nature du relais gouvernant la mise en place des curli en réponse à la présence de nickel. Aucun des régulateurs principaux de l’expression des curli ne joue un rôle décisif. Nos résultats nous conduisent à suggérer que l’effet du nickel repose sur un phénomène global de réponse au stress oxydant dont le mécanisme reste à déterminer. / Nickel is known for its use in alloy preparation, which is renowned for not being very sensitive to bacterial contamination, and thus widely used in the food-processing and medical sectors. However, bacteria appeared to be able to adhere even on this type of material, and to colonize it in the form of biofilms. Biofilms are microorganisms’ communities, adherent between themselves and to a surface, thanks to the secretion of an adhesive matrix, which offers them protection against desiccation, host defences and a great number of antimicrobial agents. Biofilms express biocidal multiresistance properties, which causes major sanitary problems in hospitals and industries. Biofilm life comes with important modifications in the genetic expression, which induces specific characteristics like increased biocides resistances and virulence factors production. In the latter, curli are a major proteic component of the extracellular matrix in the bacteria Escherichia coli and Salmonella spp., and curli play a key role in biofilm formation on inert and biologic surfaces. This work had consisted of the exploration of the biofilm life-style contribution in the survival of E. coli K-12 bacteria that produces curli in the presence of nickel. In that aim, physiological effect of soluble ions of nickel on the bacterial survival has been tested on inert supports such as polystyrene and stainless steel. We have shown that sub-inhibitory concentrations of nickel induce an increase in the biofilm thickness and density. This effect does not rely on physicochemical modifications on the bacterial surface, nor on RcnA activity, which is the only known efflux pump dedicated to nickel in E. coli. On the other hand, low concentrations of nickel induce curli expression and their production. Hence, the nickel-induced biofilm increase occurs through transcriptional activation of curli genes. This work also tried to find the nature of the relay that governs curli setting up in response to the presence of nickel. None of the curli principal regulators seem to be implicated in this curli production increase. Thus, our results suggest that nickel effect lies on a more global response phenomenon like oxidative stress, but the involved mechanism needs to be determined.