This thesis investigates the fatty acid production from carbohydrates using C. butyricum. In nature a common route for the anaerobic degradation of carbohydrate in the environment is via methanogenesis. At the heart of these processes however, is the metabolism of a diversity of carbohydrate materials that produce a few fatty acids (acetate and butyrate) which are then slowly converted to methane. In this context, fatty acids can be considered as a common end- product/intermediate from carbohydrate degradation that could be used to produce chemicals. Already, acetic and butyric acid are important feedstock chemicals in the pharmaceutical, food and industrial sectors and there is potential to expand this further. As a first step to investigate the conversion of waste carbohydrate to fatty acids for chemical production, C. butyricum, a strictly anaerobic bacterium, was investigated as a model system for the potential production of acetic and butyric acid. The production efficiency of C. butyricum relies on the type of substrate, production methodology, the strain and environmental conditions. Pure cultures of C. butyricum were investigated for fatty acid production from carbohydrates. Initial studies involved medium optimization in test tube culture for high growth rate and maximum biomass production (ODmax)- In this medium, glucose was selected as the main substrate together with yeast extract, KH2PO4 and NH4(SO)4. The studies were carried out in three types of pH controlled reactors; batch stirred tank (SRT), continuously stirred tank (CSTR) and membrane bioreactor (MBR) A comparison the fatty acid production kinetics and productivity in each reactor was undertaken and the effect of glucose concentration and where appropriate, glucose feed rates, were also investigated. The results show that fatty acid production could be carried out in all three fermentation systems. A common observation in these systems was that fatty acid production was influenced by the glucose concentration in that at low glucose concentration the ratio of acetate to butyrate was about 30:1 while at higher concentrations the ratio was reduced to about 3:1 on a molar basis. The detailed kinetic studies generated unique data for this organism and shows that the maintenance coefficient (ms) increase with increasing glucose concentration (0.02 to 1.1 g substrate/g cell/h), due to mainly to end product inhibition and the true yield (Yx/s was around 0.2 for all glucose concentrations tested. Meanwhile substrate saturation (KJ decreased with increasing glucose concentrations (2.06-6.41 g/L). This observation was atypical to that observed in other anaerobic fermentations by previous workers. A comparison of fatty acid productivities using a l0g/1 glucose feed in the 3 reactors for acetic acid were 0.95 g/l/h for STR. 4.41 g/l/h for CSTR and 37.88 g/l/h for MBR and for butyric acid 0.15 g/l/h for STR, 1.27 g/l/h for CSTR and 14.34 g/l/h MBR. Although, previous work in this area is limited the data obtained in this study was also compared with other published work and this suggests that the production of fatty acid, especially acetic and butyric acid in the MBR system is by far the most productive yet reported. The results are discussed in the context of the waste treatment process for fatty acid production and its application to waste conversion and its further development.

Zugl.: Aachen, Techn. Hochsch., Diss., 2009

Techn. Universiẗat, Diss., 2003--Berlin.

Le microbiote digestif humain joue un rôle essentiel et bénéfique pour son hôte mais il est également impliqué dans un nombre croissant de pathologies. Les connaissances sur la composition de cet écosystème ont récemment été révolutionnées grâce à l’utilisation de techniques moléculaires. Cependant, ces techniques comportent des limites importantes. C’est ainsi que le concept de « culturomique » a été introduit ; il consiste en la multiplication de milieux et conditions de culture et l’identification rapide de colonies bactériennes par spectrométrie de masse (MALDITOF) ou par amplification et séquençage du gène de l’ARN ribosomal 16S. Dans la première partie de ce travail, nous avons mis en évidence une association entre la présence de Clostridium butyricum dans les selles et la survenue d’entérocolite ulcéro-nécrosante que ce soit par méthodes de pyroséquençage et culture ou par PCR quantitative en temps réel spécifique de C. butyricum; identifié après séquençage du génome complet de toutes nos souches de C. butyricum, la présence du gène de la β-hémolysine (toxine). Dans la deuxième partie de ce travail, nous avons montré par cuturomique que les bactéries à Gram-négatif (BGN) étaient fréquemment disséminées au sein du microbiote cutané transitoire des patients hospitalisés en réanimation ; le réservoir serait essentiellement digestif. En conclusion, le microbiote digestif constitue un réservoir sousestimé de bactéries pathogènes. La microbiologie moderne incluant les nouvelles méthodes de culture permet d’étendre de manière considérable les connaissances sur la composition de cet écosystème et son implication en pathologie humaine. / He human gut microbiota plays an important and beneficial role in its host but it is also involved in a growing number of diseases. Knowledge of the composition of this ecosystem have recently been revolutionized by the use of molecular techniques. However, these techniques have significant limitations. Thus, the concept of "culturomics" has been introduced; it consists of the multiplication of culture conditions and the rapid identification of bacterial colonies by mass spectrometry (MALDI-TOF) or by PCR 16S RNA gene sequencing. In the first part of this work, we have demonstrated an association between the presence of Clostridium butyricum in the stool and the occurrence of necrotizing enterocolitis whether by pyrosequencing methods and Culture or by quantitative PCR specific real time C. butyricum; identified after sequencing the complete genome of all our strains of C. butyricum, the presence of the gene of β-hemolysin (toxin). In the second part of this work, we showed by cuturomics that Gram-negative bacteria (BGN) were frequently spread out over the transitional skin microbiota of patients hospitalized in intensive care; the reservoir would essentially digestive. In conclusion, the gut microbiota is an underestimated reservoir of pathogenic bacteria. Modern microbiology including new culture-based methods is currently extending exponentially our knowledge on gut microbiota giving rise to new insights into the pathogenesis or the transmission of infectious diseases.

La dysbiose est une cause importante dans la survenue de maladies, favorisant la prolifération de pathogènes ou induisant l’inflammation. L’étude de ce phénomène est devenue possible grâce aux approches d’analyse génomique (AG) associé avec d’autres techniques. L’entérocolite nécrosante (ECN) et l’infection du pied diabétique (IPD) demeurent deux maladies associées à la dysbiose dans lesquels différents bactéries ont été décrites, notamment C. butyricum dans l’ECN, E. coli et S. aureus dans l’IPD. Dans le cadre de l’ECN, C. butyricum demeure l’espèce la plus fréquente chez les ECN. L’identification clusters liés géographiquement et en fonction du temps. Le portage asymptomatique est suggéré par une similarité génomique des souches patients et contrôles. La prédiction d’un gène de β-hémolysine ainsi leur effet cytotoxique sur les cellules Jurkat avait été observé. De même, sur les cellules Caco-2 malgré le KO du gène de β-hémolysine. En se basant sur l’analyse physico-chimique du surnageant bactérien, nous avons suggéré que la fraction cytotoxique est protéique. La purification de la fraction cytotoxique a permis de trouver une protéine codant pour PspC family possédant un domain conservé commun avec celui de la toxine A/B. L’inactivation du gène codant pour cette protéine n’a pas supprimé l’effet cytotoxique, suggérant la présence d’une combinaison gènes. En parallèle, nous avons ciblé l’impact de C. neonatale par qRPC spécifique rpoB. Cette espèce était plus fréquente chez les patients, ainsi de clones géographiques ont été identifiées. Enfin, des SNPs ont été observés dans des gènes de virulence dans le cas des E. coli et S. aureus isolés de l’IPD. / Dysbiosis remains a main cause during the establishment of several diseases, by promoting bacterial translocation, leading to inflammation process. Specific microorganisms were involved in the pathogenesis of dysbiosis-associated diseases, notably necrotizing enterocolitis (NEC) and diabetic foot (DF). This was possible by the implication of whole-genome analysis (WGA) in association with other techniques. In case of NEC, C. butyricum was significantly associated with in NEC; tested on a South-East French cohort. Geographical and/or temporal clusters were identified, thus genomic relationship between NEC-associated isolates and controls, suggesting the presence of asymptomatic carriage. Genes encoding for β-hemolysin was detected and C. butyricum supernatant exhibited cytotoxic effect on Jurkat cells. Cytotoxic effect was also presented on Caco-2 cells. Supernatant of β-hemolysin-mutant C. butyricum showed enterotoxic effect. Basing on physico-chemical data, we assumed that the evaluated fraction was a protein. Proteomics analysis revealed that PspC family was the cytotoxic protein. This protein owned a glucan-binding domain, shared by C. difficile toxin A/B. The KO of PspC gene was enterotoxic, suggesting by this the existence of a combination of genes. In parallel, a specific rpoB-based qPCR was developed to identify C. neonatale. We found that, C. neonatale was more prevalent in NEC than in controls. Although co-identified in association with C. butyricum. C. neonatale clones were distinguished especially in strains isolated from the same hospital. Regarding to DF infection, SNPs were identified within S. aureus and E. coli genomes, especially in virulent genes.