Microaerophilic and chemotaxic diazotrophs, azospirilla are found in close association with certain cereals such as durum wheat and maize and are active in enriching these ecological niches with the macronutrient nitrogen as ammonia. Regarded as highly pleomorphic, Azospirillum spp. are highly motile, using either a single polar flagellum when grown in liquid environments or peritrichous lateral flagella in viscous environments. Additionally, azospirilla are able to adhere onto surfaces as a biological film or aggregate cell-to-cell as nonproliferating flocculi, and these two processes having been suggested as positively affecting the survival and dispersal of the bacteria in the soil. Even though both biofilm formation and flocculation have been characterized via the presence of bacterial extracellular polysaccharides, the nature of the observed exopolysaccharides is still obscure, as are the underlying molecular mechanisms facilitating their organization. Here, we identified the optimal conditions for biofilm formation as a high C:N ratio under conditions of low aeration. Cells showed an increased preference for hydrophobic plastic rather than hydrophilic glass when the bacteria were first grown in a rich medium, TY, then were subcultured in a minimal media under these conditions. Using transposon mutagenesis, we also identified metabolic and cell-surface functions perhaps involved in the flocculation potential of these bacteria and we present an initial characterization of their contribution to this cellular differentiation process.

Thesis (Ph. D.)--University of Wyoming, 2005. / Includes bibliographical references. Also available online.

Myxococcus xanthus ( M. xanthus ) is a gram-negative, rod-shaped soil-dwelling predatory bacterium. It can move on solid surfaces forming cooperative single-species biofilm in which various self-organizing patterns are observed. Under distinct environmental conditions, these bacteria can swarm outward, form travelling waves or aggregate into fruiting bodies as a result of diverse intercellular interactions, signaling and coordinated cell motility. M. xanthus colony actively expands when food is plentiful, but stops this under nutritional stress and thereafter aggregates into fruiting bodies where individual cells transform into spores. When in direct contact with their prey, M. xanthus cells form traveling cell-density waves called ripples to facilitate their predation. These patterns play an important role in maximizing M. xanthus adaption to the changing environment. While these phenomena have been studied using traditional experimental microbiology and genetics, recently it is becoming clear that system biology approach greatly complements traditional laboratory work. This thesis shows my effort to deepen the understanding of self-organization in microorganisms using statistical image processing techniques and agent-based modeling. Statistical image processing results illustrate that aggregation into fruiting bodies is a highly non-monotonic yet spontaneous process without long-range signal transduction. The agent-based model of aggregation accurately reproduces the final steady states of an aggregation process but fails to reproduce the experimental dynamics. The agent-based modeling for predatory ripples quantitatively reproduces all observed patterns based on three simple experimentally observed rules: regular cellular reversals, side-to-side contact induced early reversals and refractory period after each cellular reversal. Moreover, the agent-based model predicts that predatory ripples speed up the swarm expansion into the prey region and keep individual M. xanthus cells in the prey region longer. These predictions are all quantitatively verified by experimental observations. The combination of statistical image analysis and agent-based modeling brings greater understanding of self-organizing patterns in M. xanthus and will be essential for further research on similar patterns in other microorganisms and higher organisms.

Bacterial biofilms are surface associated colonies that are of considerable concern and interest to industry, medicine and research. They are resistant to antibiotics, their host’s defences and are able to survive under harsh conditions. Biofilm formation in many bacterial strains are dependent on the production of a polysaccharide intercellular adhesion (PIA), a beta-(1-->6)-N-acetylglucosamine polymer. Vaccines derived from biologically isolated PIA have shown efficacy against clinically isolated strains of E. coli and pathogenic strains of S. aureus in animal models. Accordingly, chemically synthesized neoglycoconjugates based on PIA glycosides will be developed to serve as lead compounds for the development of new antibiotics as well as vaccines against biofilm dependent infections. Described in this thesis is a comprehensive study of the synthesis of PIA oligosaccharides and their deacetylated equivalents, the strategy for installing a stable linker on the free reducing oligosaccharide terminus and finally the conjugation to a model carrier protein for the development of potential neoglycoprotein vaccines.

Bacterial biofilms are surface associated colonies that are of considerable concern and interest to industry, medicine and research. They are resistant to antibiotics, their host’s defences and are able to survive under harsh conditions. Biofilm formation in many bacterial strains are dependent on the production of a polysaccharide intercellular adhesion (PIA), a beta-(1-->6)-N-acetylglucosamine polymer. Vaccines derived from biologically isolated PIA have shown efficacy against clinically isolated strains of E. coli and pathogenic strains of S. aureus in animal models. Accordingly, chemically synthesized neoglycoconjugates based on PIA glycosides will be developed to serve as lead compounds for the development of new antibiotics as well as vaccines against biofilm dependent infections. Described in this thesis is a comprehensive study of the synthesis of PIA oligosaccharides and their deacetylated equivalents, the strategy for installing a stable linker on the free reducing oligosaccharide terminus and finally the conjugation to a model carrier protein for the development of potential neoglycoprotein vaccines.

No description available.

The role of natural biofilms affecting the water quality in rivers has been the main theme in this study. Firstly, the study developed the capacity of biofilms in retention and/or production of DOC. Secondly, the study also approached the production of the geosmin metabolite by benthic cyanobacterial mats. In the two developed aspects, the structure and function of the biofilms showed their relevance in evaluating the capacity of biofilms on the amelioration of the water quality. The importance of the biofilms on ecological research in running waters has been focus in their capacity of adsorption and transformation of nutrient, and therefore, in the self-purification capacity of streams and rivers. Biofilms are also major sites of carbon cycling in streams and rivers, affecting the water DOC dynamics. Eutrophication of streams and rivers have been also linked with an increase of algal biomass. As a consequence, the massive growth of cyanobacterial mats can cause the production of toxic and nuisance metabolites, like geosmin, a secondary metabolite which causes earthy and musty taste and odor in the water.The first conclusion of this study was that biofilms may play an important role in the retention of water DOC. We elucidated whether biofilms act as sinks or sources of fluvial DOC, depending on their structure and biomass accumulation. Metabolism (extracellular enzymatic activity) and structure (algae, bacteria, C/N content) of light-growth and dark-growth systems were analyzed over a year. Biofilms from the light-growth regime presented monthly variation in DOC uptake/release rates, but the annual average presented higher DOC uptake than dark-growth biofilms. However, the latter had a constant DOC consumption along the year, permitting a maintenance of low water DOC levels. The biofilm structure and the relative contribution of autotrophs and heterotrophs had a relevant implication in the carbon recycling, since metabolic activities were affected by variations in this structure.Geosmin production was related with the massive growth of benthic cyanobacteria (formed mainly by Oscillatoria limosa) in littoral zones, where water velocity was low, warmer temperatures and high nutrient concentration and low N/P ratio. The masses were further detached and drift downstream, being the responsible for the dispersion of geosmin along the river. The high biomass accumulation per surface unit, may cause a nutrient depletion inside the mat, e.g. nitrogen limitation. Structural and functional differences were found in the different fractions of the cyanobacterial mat (attached vs. free-floating). Free-floating mats presented higher biomass and exoenzymatic activities. Otherwise, the low phosphatase/aminopeptidase ratio found in both compartments indicated a nitrogen limitation inside the mats. Microstructural analyses with oxygen and redox microsensors have been useful to understand the function of the different cyanobacterial patches inside the mat. During the dark, Oscillatoria micro-patches aggregated and accumulated in thick masses where some anoxia conditions were found, giving a very low redox potential. This low diffusion could be associated with resource depletion, limiting the nutrient availability and defining the appropriate conditions for the geosmin production.

Microaerophilic and chemotaxic diazotrophs, azospirilla are found in close association with certain cereals such as durum wheat and maize and are active in enriching these ecological niches with the macronutrient nitrogen as ammonia. Regarded as highly pleomorphic, Azospirillum spp. are highly motile, using either a single polar flagellum when grown in liquid environments or peritrichous lateral flagella in viscous environments. Additionally, azospirilla are able to adhere onto surfaces as a biological film or aggregate cell-to-cell as nonproliferating flocculi, and these two processes having been suggested as positively affecting the survival and dispersal of the bacteria in the soil. Even though both biofilm formation and flocculation have been characterized via the presence of bacterial extracellular polysaccharides, the nature of the observed exopolysaccharides is still obscure, as are the underlying molecular mechanisms facilitating their organization. Here, we identified the optimal conditions for biofilm formation as a high C:N ratio under conditions of low aeration. Cells showed an increased preference for hydrophobic plastic rather than hydrophilic glass when the bacteria were first grown in a rich medium, TY, then were subcultured in a minimal media under these conditions. Using transposon mutagenesis, we also identified metabolic and cell-surface functions perhaps involved in the flocculation potential of these bacteria and we present an initial characterization of their contribution to this cellular differentiation process.

Thèse de doctorat : Chimie et Physico-Chimie Moléculaires : Nancy 1 : 2007. / Titre provenant de l'écran-titre. Bibliogr.

Thèse de doctorat : Sciences pour l'ingénieur : Strasbourg 1 : 2008. / Titre provenant de l'écran-titre. Bibliogr. p. 155-161.