Different factors such as growing environmental awareness due to the increasing negative impact of persistent plastic wastes, the uncontrollable price variations of the raw material and the rapid depletion of  reserves have increased the interest in research regarding polymers derived from renewable sources to replace petroleum-based materials. One of the earth’s most abundant macromolecules is cellulose. The production of cellulose from another resource replaces and reduces the demand from plants, the other resource being cellulose from a bacterial system. Bcaterial cellulose film were produced by fermenting apple waste (apple pomace) from cider production donated by Herrljunga Cider in Herrljunga, Sweden and expired fruit juice, produced by LoveJuice Indonesia, containing a mixture of fruits, mainly apple. As inoculum for the fermentations two different Kombucha cultures were used. To optimize the fermentation conditions, factors such as nitrogen source, sugar content, temperature, pH, surface area, sterilization of the substrate, culture condition and fermentation time was varied to obtain the desired result. The bacterial cellulose films were dried at 50-70 °C in an oven, air-dried or freeze-dried to evaluate the impact of drying technique on the final material. The behavior of the microorganism during fermentation was monitored by sampling and observation. The consumption rate of carbohydrates was analyzed using high performance liquid chromatography (HPLC). The properties of the obtained biofilms were analyzed using thermogravimetric analysis (TGA), tensile testing and determination of cellulose content in the obtained biofilms. Two different sugar concentrations (35 g/l and 70 g/l) and three different caffeine concentrations (0 g/l, 150 g/l and 225 g/l) as nitrogen source were investigated to determine the best condition. A control batch of conventional (black tea and 70 g/l table sugar) Kombucha was used as reference. The highest tensile strength (50 MPa) and thermal stability was observed in the biofilms with the highest yield that had been dried in oven. The biofilms obtained by fermenting apple pomace from the cider industry showed the highest tensile strength and highest thermal stability in comparison to fermenting expired fruit juice. The biofilm obtained by fermenting apple waste(sugar concentration 70 g/l) in combination with sterilizing the substrate without adding any nitrogen source, dried in an oven and purified using 0,1 M NaOH resulted in the highest tensile strength, highest thermal stability and the purest biofilm from a visual aspect. The highest yield was observed in the fermentation of apple pomace (sugar concentration 70 g/l) from the cider industry without sterilization of the initial media with an addition of nitrogen of approximately 450 mg/l). The optimal fermentation period was observed to be 14-15 days, at 25-28 °C under static conditions using a glass vessel with a diameter of 20 cm and an initial pH of 5,5.

Les bactéries pathogènes Escherichia coli entérohémorrhagiques (EHEC) O157:H7 causent des toxi-infections sévères chez l’humain. Les biofilms des EHEC rendent difficile leur contrôle dans les environnements favorisant leur persistance. Certaines souches O157:H7 dont celle de référence Sakai, possèdent une capacité accrue à s'autoagréger et former des biofilms. L’étude a visé à identifier les gènes impliqués dans l’autoagrégation et la formation de biofilm chez la souche Sakai, et vérifier l’association des facteurs identifiés avec d’autres EHEC O157:H7 du même phénotype. Avec une banque de mutants Tn10 de la souche Sakai, des mutants non-autoagglutinants et non-formateurs de biofilms des gènes csgB et csgG furent sélectionnés et caractérisés. Ces mutants formaient significativement moins de biofilms et d´autoagrégats que Sakai, et ne produisaient plus curli. La complémentation des mutants restaurait le phénotype sauvage. De plus, des gènes responsables de la biogenèse de curli csgA, csgB et csgG étaient significativement surexprimés chez Sakai, comparativement avec la souche EDL933 non-autoagglutinant, qui forme moins de biofilm. Parmi les souches d’E. coli 0157:H7 on distingue deux groupes d’isolats: Sakai-like et EDL933-like selon leur production de curli, et leur capacité à former des autoagrégats et biofilms. Nos résultats suggèrent qu’une surproduction de fibres de curli dans un sous-ensemble de souches O157:H7 pourrait être responsable de leur phénotype particulier d'autoagrégation et de formation de biofilms forts. Le projet permet de mieux cerner le mécanisme de formation de biofilm dans EHEC et renforce l’hypothèse que le curli est une cible intéressante pour contrer la persistance des EHEC en environnements naturels et industriels. / Enterohemorrhagic E. coli (EHEC) O157:H7 is an important foodborne pathogen that causes severe toxi-infections in humans. These bacteria have a higher capacity to form biofilm, impeding the control of the contamination in different environments and allowing their persistence. Some E. coli O157:H7 strains, including the Sakai reference strain, display a distinctive ability to autoaggregate and form strong biofilms. The aim of this work was to identify the genes involved in autoaggregation and biofilm formation in Sakai strain, and to verify the association between identified factors and the same phenotype in other EHEC O157: H7. We found that csgA, csgB and csgG curli genes were significantly overexpressed in strain Sakai compared to strain EDL933, a low biofilm-former and non-autoaglutinating strain. Sakai csgB and csgG Tn10 mutants formed significantly less biofilm and autoaggregation than the wild-type strain, and lost the curli-producing phenotype. Complementation restored the strong autoaggregation and biofilm formation phenotype, and the curliated morphotype of Sakai. In addition, E. coli O157: H7 isolates tested for curli formation, Sakai-like strains were curli-producing, whereas EDL933-like strains were non-curliated. These results suggest that overproduction of extracellular curli fibers in a subset of E. coli O157: H7 strains may be responsible for their particular phenotype of autoaggregation and strong biofilm formation. The project provides a better understanding of the mechanism of biofilm formation in EHEC, as well as reinforcing the hypothesis that curli fibers are an attractive target to counter the persistence of these bacteria in natural and industrial environments.

No description available.

Le bacille de la peste, Yersinia pestis, a une vie parasitaire au cours de laquelle il oscille le plus souvent d’un hôte mammifère à l’autre par l’intermédiaire des puces, et plus rarement par voie aéroportée. Comme tel, Yersinia pestis doit rapidement ressentir et répondre aux variations brutales de son environnement afin se maintenir dans la nature. C’est pourquoi, nous avons étudié le rôle des systèmes de régulation à deux composants dans la peste compte tenu que ces systèmes sont connus pour avoir un rôle clef dans l’adaptation des bactéries aux changements environnementaux. En plus du système PhoP-PhoQ dont l’importance chez le mammifère et la puce a été précédemment révélée, nous avons découvert que quatre systèmes sont requis pour le cycle de la peste. Plus particulièrement, l'un d'entre eux permet une colonisation optimale du tube digestif de la puce alors que les 3 autres systèmes sont impliqués dans la production de biofilm, un processus indispensable à une transmission optimale du bacille par les puces. Nous avons aussi découvert que le système OmpR-EnvZ est l’unique système, en plus du système PhoP-PhoQ, requis pour la production de la peste bubonique, septicémique et pulmonaire. Nos travaux, menés in vitro, ex-vivo et in vivo suggèrent que le rôle du système OmpR-EnvZ serait de protéger la bactérie contre les effecteurs toxiques sécrétés par les polynucléaires neutrophiles dans les tissus et, ceci tout au long du processus infectieux. / Plague bacillus, Yersinia pestis has a parasitic lifestyle in which it is mainly transmitted between mammilian hosts through the bite of infected fleas, and in rare cases through infected droplets. Thus, Yersinia pestis must rapidly sense and respond to wide and brutal changes of its environment in order to survive. We aimed at decipher the role of two component regulatory systems in plague, as they are known to be key players in bacterial adaptation to the environment. In addition to the already described PhoP-PhoQ system, we found out that four systems are required for plague cycle. We showed that one of these systems is important for an optimal colonization of the flea's digestive tract, while the three others are required for biofilm production, an essential step in the bacillus transmission by the fleas. We also found out that OmpR-EnvZ, in addition to PhoP-PhoQ, is the only one to be important to produce bubonic, septicemic and pulmonary plague. Our in vitro, ex-vivo and in vivo works suggest that the OmpR-EnvZ system would be to protect bacterial against toxic effectors that are produced by polymorphonuclear leukocytes all along the infectious process.

Lactobacillus- Spezies, die zur Gattung der Milchsäurebakterien gehören, haben bereits hemmende Eigenschaften gegen Candida albicans gezeigt. Dieser dimorphe Hefepilz ist einer der bedeutendsten Erreger von Pilzinfektionen beim Menschen und einer der häufigsten Verursacher Katheter- assoziierter Infektionen. Eine bedeutende Rolle bei der Pathogenität von C. albicans spielt die Biofilmbildung, die sowohl die körpereigene Abwehr als auch die antimykotische Therapie einer invasiven Infektion erheblich erschwert. Zu den Virulenzfaktoren zählt eine Vielzahl von Genen, darunter auch die sekretorischen Aspartylproteasen (SAPs), die zur Infektion sowohl in vitro als auch in vivo beitragen. In der vorliegenden Arbeit wurde der Einfluss verschiedener Lactobacillus- Stämme auf die Biofilmbildung des invasiv pathogenen C. albicans SC 5314 und des in der Pathogenität abgeschwächten Stammes ATCC 10231 untersucht, sowohl phänotypisch als auch hinsichtlich der metabolischen Aktivität durch den semi- quantitativen XTT- Reduktions- Assay. Zudem erfolgten Expressionsanalysen ausgewählter Gene von C. albicans, deren Zusammenhang mit der Biofilmbildung und Pathogenität bekannt ist. Dabei konnte gezeigt werden, dass L. johnsonii DSM 10533 die metabolische Aktivität beider C. albicans- Stämme erheblich verringern kann (um bis zu 80%) und auch einen phänotypisch drastisch reduzierten Biofilm verursacht. In Anwesenheit dieses Stammes kam es zu stark verringerter Aktivität der beobachteten SAP- Gene vor allem des invasiven Stammes C. albicans SC 5314. Andere Pathogenitäts- assoziierte Gene wie Als 3 und Hwp 1 wurden dagegen eher hochreguliert. L. rhamnosus DSM 20021 und ein klinisches Isolat verursachten ebenfalls eine Verringerung der metabolischen Aktivität, sorgten phänotypisch aber eher für vermehrte Hyphenbildung des Pilzes. Ersterer verursachte eine deutlich reduzierte Aktivität von Hwp 1 und Ume 6 bei C. albicans ATCC 10231. L. reuteri DSM 20016 zeigte keinen signifikanten Einfluss auf Biofilmbildung, Aktivität und Genexpression der beobachteten C. albicans- Stämme. Diese Ergebnisse zeigen deutlich, dass unterschiedliche Lactobacillus- Stämme sich in ihrem Einfluss auf C. albicans erheblich unterscheiden. Auch die Reaktion verschiedener C. albicans- Stämme auf Lactobacillus- Spezies ist sehr verschieden. In dieser Arbeit zeigte L. johnsonii DSM 10533 ein deutliches Potential, C. albicans in der Biofilmbildung und Expression von Pathogenitätsfaktoren zu hemmen. Dieser Stamm erscheint damit für weiterführende Untersuchungen hinsichtlich probiotischen Potentials geeignet. Die Ergebnisse einer Lactobacillus Spezies können nicht generell auf andere Lactobacillus Spezies übertragen werden. Ob sich innerhalb einer Spezies alle Stämme gleichermaßen verhalten, bedarf ebenfalls der Überprüfung. Die Ergebnisse dieser Arbeit werfen auch die Frage auf, ob Lactobacillus Spezies sogar die Pathogenität von C. albicans erhöhen können.

Carbon-infiltrated carbon nanotube (CICNT) forests are carbon nanotube (CNT) forests infiltrated with pyrolytic carbon to increase durability by becoming a solid material. This material can be tuned to maintain the nanotube geometry of a CNT forest and can also be fabricated on a variety of materials and geometries. Additionally, the present work has indicated that CICNT forests may resist bacterial proliferation and biofilm formation. This phenomenon is not due to the CICNT chemistry; it is presumably due to the CICNT nanostructure morphology. Thus, both silicon and stainless steel substrates were used to investigate CICNT's structural resistance to Methicillin-resistant Staphylococcus aureus (MRSA) biofilm. From in vitro experimental testing, CICNT on both these substrates resisted MRSA cell attachment and biofilm proliferation. The discovery of this non-pharmaceutical biofilm resistance expands the potential applications of CICNT to include medical devices that are prone to infection and/or devices that contribute to infection. Two representative applications were investigated: external fixator pins and scalpel blades. CICNT-coated versions of these applications underwent additional MRSA biofilm resistance testing as well as mechanical testing. In particular, external fixator pins were identified as a high potential application of CICNT surface coating technology. Previous work on both CNT and CICNT forests has largely been performed on planar structures. However, any potential medical device applications involve curved substrates. In particular, concave curvatures are challenging due to the potential for stress-related CICNT forest defects. Thus, the present work also included a study of the incidence rates and determining factors of these defects. SEM images of the cross-sections revealed different types of microscale forest defects while the top surface showed morphologies that are largely consistent with flat substrates. CICNT forest height and substrate curvature were identified as contributing factors to CICNT forest defect incidence rates. Thus, the present work advances the understanding of bacterial resistance and microstructure-related properties of CICNT surface coatings, with applications in medical devices.

The nitrification process, the biologically mediated process of ammonia treatment in water resources recovery facilities (WRRF), remains the most common treatment process to mitigate the adverse effects of effluent ammonia discharges in surface water. However, it is well established that the temperature-sensitive process of nitrification remains hindered at low temperatures in conventional suspended growth technologies; specifically, passive treatment systems such as the lagoons, representing over 50% of Canadian treatment facilities in operation. As such, nitrification in lagoon facilities remains unreliable during the cold seasons with no nitrification occurring at 1°C. In contrast to suspended growth systems, attached growth technologies such as the moving bed biofilm reactors (MBBR) have recently been proven capable of achieving significant nitrification rates at temperatures as low as 1°C and are proposed as suitable upgrade systems to the common lagoon facility to reach year-long ammonia treatment targets. As such, the main objective of this research is to investigate and expand the current knowledge by investigating the key research questions lacking in the current literature on post-carbon, low temperature nitrifying MBBR systems. With this aim, a temperature-controlled study of attached growth nitrification kinetics was conducted to isolate the effects of low temperatures on nitrifying MBBR system performance down to 1°C. A removal rate of 98.44 ± 4.69 gN/m³d is identified as the 1°C intrinsic removal rate and the design removal rate for nitrifying MBBR systems at low temperatures. Considering this intrinsic rate at 1°C, an assessment of reactor efficiency at elevated TAN concentrations typical of non-combined sewer systems indicates that a two reactor in-series MBBR system configuration is recommended for retrofitting lagoon facilities connected to sanitary sewers. The study of the reactor performance to temperatures as low as 1°C demonstrates a non-linear decline in removal efficiency between 10°C and 1°C, with the existence of a kinetic threshold temperature delineated between 4°C and 2°C. As such, this delineated temperature range accounts for a significant decline in the performance of low carbon nitrifying MBBR systems during the onset of the cold seasons. This research identifies new recommended Arrhenius correction coefficient values taking into account this kinetic threshold temperature, with a coefficient of 1.049 being recommended above the kinetic threshold (≥4°C) and 1.149 below the threshold temperature at 1°C. Moreover, since the elapsed time to low temperature was identified as a key factor of attached growth nitrification kinetics, a modified theta model accounting for temperature and time is proposed in this research to accurately model the rate of nitrifying MBBR systems between 4°C and 1°C. Finally, with the severe adverse effects of sudden decreases in temperature, or cold shocks, on nitrification kinetics being previously demonstrated but not well understood, this research compares acclimatized and cold shocked MBBR reactors down to 1°C. The findings indicate 21% lower kinetics in the cold shocked reactor with reactor efficiencies never reaching those of the acclimatized reactor despite extended operation at 1°C. Thus, the research delineates the potentially lasting effects of extreme weather events such as cold air outbreaks and snowmelt periods on nitrifying MBBR system performance. On the other hand, these same findings demonstrate the resiliency of nitrifying MBBR reactors as nitrification was maintained within these systems despite being cold-shocked down from 10°C and 1°C. This study of attached growth kinetics was coupled with an investigation of the nitrifying biofilms, biomass, and microbiome responses to low temperatures and cold shock down to 1°C to provide an understanding of the changes occurring in these systems down to the cellular level. Comparisons of acclimatized and cold shocked nitrifying biofilms responses down to 1°C were characterized by increases in biofilm thickness, increases in biomass viability; and, greater shifts in microbiome communities occurring above 4°C in the acclimatized biofilm. Considering these observations, results also indicated a significant increase in nitrifiers per carrier above 4°C. As such, these findings suggested that the bulk of nitrifying biofilm adaptation to cold temperatures occurs above 4°C, a crucial adaptation phase in acclimatized systems. This adaptation phase is shown to be lacking in cold-shocked systems, with the cold shocked biofilm and microbiome demonstrating significant differences with the acclimatized systems’ biofilm and microbiome. This research was performed to answer the critical research questions relating to the design and operation of the post-carbon, low temperature nitrifying MBBR systems, with the first low temperature MBBR systems being scheduled to begin operation in the fall of 2020. This research expands the current knowledge on low temperature attached growth nitrification kinetics as well as cold shocked attached growth nitrification kinetics in MBBR systems down to 1°C. In addition, this research delineates the effects of low temperatures and cold shocks on the nitrifying MBBR system’s biofilms and their embedded cells.

Listeria monocytogenes est une bactérie à Gram positif impliquée dans des infections graves d’origine alimentaire. La plupart des cas de listériose humaine sont causés par la consommation d'aliments réfrigérés prêts à consommer. La capacité de ces bactéries à survivre et à se multiplier dans une large gamme de conditions difficiles fait de ce pathogène une des préoccupations majeures dans les industries agro-alimentaires. Ces propriétés de L. monocytogenes sont renforcées par son aptitude à former des biofilms. Le but de ce projet était d'explorer l'adaptation de ce pathogène à la déshumidification et aux basses températures par deux approches de protéomique. La première approche, basée sur la technique d’imagerie par spectrométrie de masse (IMS) MALDI-TOF, permet de réaliser la cartographie de molécules à partir d'échantillons biologiques. Ce travail a consisté à développer cette approche, en considérant un biofilm bactérien comme un tissu, afin d’accéder à des informations sur la distribution de protéines dans des biofilms de L. monocytogenes soumis à un stress de déshumidification. En outre, une approche LC-MS/MS a été utilisée pour relier les données spectrales d’intérêt obtenues par l'IMS et l'identification des protéines. L’IMS a permis d'examiner la distribution de 47 protéines de bas poids moléculaire dans les biofilms. Cinq protéines ont été identifiées par LC-MS/MS grâce aux données m/z de l’IMS, y compris deux protéines de choc thermique. Les résultats démontrent que l'IMS peut être utilisée pour disséquer le protéome spatial d'un biofilm bactérien. La deuxième approche protéomique a consisté en une comparaison semi-quantitative relative et sans marquage (shotgun proteomic) des protéines exprimées dans différentes conditions de culture. Par cette méthode, nous avons exploré l’expression protéique en fonction du mode de croissance (biofilm vs planctonique) et de la température (10°C, 25°C et 37°C). Parmi les 920 et 931 protéines uniques identifiées, provenant respectivement de cellules sessiles et planctoniques, beaucoup sont liées à des fonctions cellulaires de base, mais certaines sont liées à la thermorégulation. Des changements ont été observés dans le protéome de L. monocytogenes en biofilm par rapport aux cellules planctoniques, ce qui indique des modes de régulation différents selon le mode de croissance. Ces comparaisons de l'expression des protéines dans plusieurs conditions (modes de croissance, températures) enrichiront les bases de données et aideront à modéliser les circuits de régulation qui conduisent à l'adaptation de L. monocytogenes aux environnements. / Listeria monocytogenes is a Gram-positive bacterium implicated in serious food-borne infections. Most cases of human listeriosis are caused by the consumption of refrigerated ready-to-eat foods. The ability of these bacteria to survive and multiply in a wide range of harsh conditions make this pathogen a major concern in agro-food industries. These properties of L. monocytogenes are enhanced by its ability to form biofilms. The aim of this project was to explore the adaptation of this pathogen to dehumidification and low temperatures by two proteomic approaches. The first approach, based on the MALDI-TOF mass spectrometry imaging (IMS), allows the mapping of molecules from biological samples. This work aimed to develop this approach, considering a bacterial biofilm as a tissue, in order to access information on the distribution of proteins in L. monocytogenes biofilms subjected to a dehumidification stress. In addition, an LC-MS/MS approach was used to link spectral data of interest obtained by IMS and protein identification. The IMS allowed to examine the distribution of 47 low molecular weight proteins within the biofilms. Five identified proteins were assigned by LC-MS/MS using IMS m/z data, including two cold-shock proteins. The results demonstrate that imaging can be used to dissect the spatial proteome of a bacterial biofilm. The second proteomic approach consisted on a relative semi-quantitative label-free (shotgun proteomic) comparison of proteins expressed under different culture conditions. With the method, we explored protein expression according to the mode of growth (biofilm vs planktonic) and temperature (10°C, 25°C and 37°C). Throughout the 920 and 931 unique proteins identified, from sessile and planktonic cells, respectively, many are connected to basic cell functions, but some are linked with thermoregulation. A shift was observed in the proteome of L. monocytogenes biofilms compared to planktonic cells indicating different patterns of regulation according to the mode of growth. These comparisons of protein expression throughout several conditions (mode of growth and temperatures) will enrich databases and help to model regulatory circuitry that drives adaptation of L. monocytogenes to environments.

Les modifications de structure et de diversité des communautés biologiques au sein d’un écosystème soumis à une perturbation, se traduisent généralement par la raréfaction, la disparition d’espèces sensibles et/ou l’apparition de nouvelles espèces tolérantes ou par la prolifération d’autres espèces tolérantes déjà présentes mais à une faible densité. Dans le cas d’une perturbation d’origine toxique, ceci a pour conséquence une diminution de la sensibilité globale de la communauté par rapport à la (aux) substance(s) responsable(s) de cette modification de structure et de diversité. L’évaluation de la tolérance vis-à-vis d’un toxique peut donc nous permettre de révéler a posteriori l’exposition d’une communauté biologique à ce toxique, en mettant en évidence le lien entre pression et impact sur le compartiment biotique d’un écosystème. Malgré de nombreux travaux en ce domaine, il reste cependant de nombreuses lacunes scientifiques dans la compréhension de cette tolérance induite par les pollutions (PICT). Le modèle d’étude retenu est le biofilm aquatique (ou périphyton), dont les spécificités biologiques et écologiques en font un outil d’étude très intéressant. Ce travail a permis de montrer que l’intégration du concept PICT comme un outil complémentaire dans les systèmes d'évaluation environnementale donnerait plus de pertinence écologique et de spécificité écotoxicologique à la batterie actuelle des bioindicateurs utilisés. Par ailleurs, le PICT est aussi une approche conceptuelle, à l’échelle des communautés, très riche et qui confirme l’intérêt d’aborder l’écotoxicologie avec le regard de l’écologue plus holistique que celui du toxicologue. En effet, les mesures de tolérance-induite qui prennent en compte la diversité fonctionnelle du biofilm, ainsi que les analyses taxonomiques associées, nous ont permis une meilleure compréhension de la résistance et de la résilience de cet écosystème suite à des perturbations d’origine chimique. Nos travaux nous ont aussi permis d’aborder le concept des seuils de résistance et de résilience écologiques, et de mettre en évidence le fait qu’une acquisition de tolérance à un stress donné, pourrait se traduire par le déplacement des communautés d’un état initial vers un état « alternatif » stable, même après le retrait du stress. Ces seuils écologiques ainsi que cet état alternatif stable signifient que la disparition des espèces les plus sensibles (comme l'un des processus expliquant le PICT) n'affecte donc pas les fonctions de la communauté dans son ensemble au début et ce seulement jusqu’à un certain seuil de résistance. Le PICT pourrait ainsi se traduire par une réduction de la diversité ou avec des modifications dans la composition spécifique, sans pour autant qu’il y ait un effet négatif sur le fonctionnement de la communauté. Cependant, la capacité des communautés à devenir tolérantes à une perturbation peut avoir des conséquences négatives sur les capacités de résilience et de résistance des écosystèmes. Nous avons donc abordé dans nos travaux le concept de « co-tolérance négative entre espèces » et de coût de la tolérance. / Changes in structure and diversity of biological communities within ecosystems subjected to disturbances are generally synonymous of the scarcity, loss and/or the emergence of new tolerant species or by the proliferation of other species already present but at low density. This leads to a decrease in the overall sensitivity of the community toward the substance(s) responsible for this change of community structure and diversity. The evaluation (and if possible the quantification) of tolerance towards a toxicant may therefore enable us to reveal a posteriori the exposure of a biological community to this toxicant (its exposure history), and demonstrate the specific link between pressure and impact on the biotic compartment of an ecosystem and, more generally, on the ecosystem. Despite numerous studies in this area, there are still many gaps in scientific understanding of the pollution induced-tolerance. The biological model that we used is the lotic biofilm (or periphyton) whose biological and ecological characteristics make it a very interesting tool for study. This work has shown firstly that the integration of the acquired tolerance concept as a complementary tool in the environmental assessment systems would allow more ecological relevance and ecotoxicological specificity to the current set of used bio-indicators. Furthermore, the PICT is also a conceptual approach at the community level, which confirms the interest to address ecotoxicology from the viewpoint of the ecologist that is more holistic than the toxicologist one. Indeed, measures of pollution-induced tolerance, by taking into account the functional diversity of biofilms, and the associated taxonomic analysis, allowed to have a better understanding of resistance and resilience of the ecosystem submitted to chemical perturbations. Our works enabled us to tackle the concept of ecological thresholds of resistance and resilience, and to highlight the fact that enhanced tolerance to a given stress, could result in the displacement of communities from an initial state to an « alternative » stable state, even after the stress removal. These ecological thresholds and the alternative stable state mean that the disappearance of the most sensitive species (as a process explaining the PICT) does not affect the functions of the community until reaching a threshold of resistance. Thus the PICT could correspond to a reduction in diversity or changes in species composition, without having a negative effect on the functioning of the community. However, the ability of communities to be tolerant toward disturbance can have negative consequences on the resilience and resistance of ecosystems. Consequently, we addressed in our work the concept of "negative co-tolerance between species" and costs of tolerance.

Indiana University-Purdue University Indianapolis (IUPUI) / Objective: The aim of this study is to investigate the effects of cinnamon water extract on nicotine-induced Streptococcus mutans biofilm. This study utilized S. mutans biofilm assays with varying concentrations of nicotine/cinnamon water extract levels. Design: A preliminary experiment was carried out to confirm the most likely effective concentration of cinnamon water extract on S. mutans biofilm. Then a 24-hour culture of S. mutans UA159 in microtiter plates was treated with varying nicotine concentrations (0-32 mg/ml) in TSBS at the same time with or without the optimum cinnamon water extract concentration. A spectrophotometer was used to determine total growth absorbance and planktonic growth. The microtiter plate wells were washed, fixed and stained with crystal violet dye and the absorbance measured to determine biofilm formation. Results: The results indicated that cinnamon water extract was able to inhibit biofilm formation significantly (p<0.05) at 5 mg/ml cinnamon water extract, therefore, 5 mg/ml of cinnamon water extract was recognized as the MIC for S. mutans biofilm formation. When combined with nicotine, cinnamon water extract sub-MIC (2.5 mg/ml) demonstrated a significant inhibitory effect (p<0.05) in biofilm and total absorbance measures at high concentrations of nicotine (8 mg/ml and above). In addition, cinnamon water extract showed a significant effect (p<0.05) at very low concentrations of nicotine (0.25 and 0.5 mg/ml) in all measures (biofilm, planktonic and total absorbance). However, at low concentrations of nicotine (2 and 4 mg/ml), there was a significant increase (p<0.05) in biofilm growth, whereas planktonic growth was significantly (p<0.05) decreased at the same concentrations. Conclusion: These results provided more evidence regarding the negative effects of nicotine and also demonstrated the positive influence of cinnamon water extract in reducing nicotine-induced biofilm formation, which needs be confirmed by in-vivo studies.