Eubiosis and dysbiosis: the two sides of the microbiota

The microbial ecosystem of the gastrointestinal tract is characterized by a great number of microbial species living in balance by adopting mutualistic strategies. The eubiosis/dysbiosis condition of the gut microbiota strongly influences our healthy and disease status. This review briefly describes microbiota composition and functions, to then focus on eubiosis and dysbiosis status: the two sides of the microbiot

Evaluation of leakage of microbial contamination from Gemini space suit Final report

Leakage of microorganisms from pressurized Gemini space suit into ambient temperature microbiotan

Physiological Aspects of Genetics

A considerable amount of evidence indicates that desoxyribonucleic acid is capable of duplicating itself, a property also possessed by genes. (By a self-duplicating material, we mean one which plays some essential role in its own production.) Watson & Crick (1) have proposed a new structure for desoxyribonucleic acid which not only takes into account the existing analytical and x-ray diffraction data but also seems capable of explaining the mechanism of duplication. Their model consists of two helical chains coiled around the same axis, the purine and pyrimidine bases on the inside, the phosphate groups on the outside. The chains are held together by hydrogen bonds between the bases, the adenine residues of either chain being bonded specifically to thymine in the other, and similarly guanine to cytosine. The sequence of bases along one chain is not restricted, but once fixed the sequence along the other chain is determined. This complementarity, which is the most novel feature of the structure, suggests that duplication takes place by separation of the two chains, followed by the synthesis of its complement alongside each chain. The model is supported by recent x-ray diffraction studies (2, 3)

The mucosal firewalls against commensal intestinal microbes

Mammals coexist with an extremely dense microbiota in the lower intestine. Despite the constant challenge of small numbers of microbes penetrating the intestinal surface epithelium, it is very unusual for these organisms to cause disease. In this review article, we present the different mucosal firewalls that contain and allow mutualism with the intestinal microbiot

A colony count model for the control of drinking water distribution systems

De nombreux paramètres sont mesurés aux usines de production d'eau potable pour contrôler l'efficacité du traitement : pH, turbidité, concentration en désinfectant... Cependant, l'eau traitée n'est pas un produit fini; sa qualité, notamment microbiologique, peut évoluer en cours de distribution. La livraison d'eau aux consommateurs peut ainsi être considérée comme l'étape finale du processus de production d'eau potable. La complexité du contrôle de la qualité de l'eau en cours de distribution repose sur l'identification des points d'échantillonnage et du nombre de prélèvements. L'objectif de cette étude est de sélectionner un paramètre de contrôle de la recroissance microbienne pour développer un contrôle de qualité plus rigoureux et précis de l'eau de distribution. Deux paramètres ont été étudiés en tant que paramètres potentiels de contrôle : le temps de séjour de l'eau dans le réseau et la matière organique biodégradable. S'il est possible de démontrer que ces paramètres ont une influence significative sur la qualitê microbiologique, ils pourront être utiles à l'identification des points d'échantillonnage et à la détermination des nombres minimaux de prélèvements. Le temps de séjour a été déterminé dans un réseau en antennes, puis dans un réseau légèrement maillé. Ce paramètre a été calculé à partir de mesures de débit et de volume de réservoirs. Les conditions de mélange parfait dans les réservoirs et d'écoulement piston dans les canalisations ont été supposées. La détermination du temps de séjour a ensuite été validée par des traçages au chlorure de sodium. La mesure du carbone organique dissous (COD) naturellement consommé dans le réseau a été préférée, pour sa simplicité et son plus faible coût, aux analyses reposant sur la biodégradation de la matière organique in vitro. Ces déterminations reposent sur la différence entre les teneurs en COD de l'eau traitée et de l'eau en cours de distribution. Un modèle prédictif du nombre de micro-organismes déterminé sur gélose et fonction du temps de séjour a été développé. La fonction logistique, souvent appliquée à la croissance des micro-organismes dans des réacteurs de laboratoire, a été choisie comme modèle. Deux paramètres microbiologiques ont été considérés : le nombre de micro-organismes déterminé à 20ºC après trois jours (N3D) et quinze jours (N15D) d'incubation. La fonction logistique a été ajustée, à un niveau de signification inférieur à 0.05, aux données de N3D et N15D collectées en hiver, au printemps et en été dans un réseau faiblement maillé. L'ajustement du modèle à différentes saisons et différentes parties d'un réseau a permis de mettre en évidence les facteurs influençant la recroissance microbienne et par conséquence les coefficients du modèle : la saison, l'origine de l'eau (eau de surface, eau souterraine) et le type de conduite. Le modèle de N3D a permis de localiser et d'estimer la quantité d'eau de distribution dont le paramètre N3D est supérieur au niveau guide européen. Ce modèle a aussi été appliqué à la localisation de postes de rechloration sur le réseau.L'utilisation de la mesure de la matière organique biodégradable en tant que paramètre de contrôle de process a été évaluée à partir de la mesure de la corrélation partielle entre le COD consommé dans le réseau et N3D et N15D. La corrélation partielle permet, dans ce contexte, de mesurer uniquement le lien entre le COD consommé dans le réseau et le nombre de micro-organismes en supprimant les interactions avec d'autres paramètres tels que le temps de séjour. Les résultats ont montré que pour les trois réseaux étudiés aucune corrélation partielle significative n'a été observée entre ces deux paramètres. Le COD consommé dans le réseau ne peut pas être utilisé efficacement comme paramètre de contrôle.The purpose of this study is to select a process control parameter for monitoring microbial regrowth in a network and to develop a more accurate and relevant quality control of supply water. Two parameters were examined as potential process control parameters: the water residence time in the network and the concentration of biodegradable organic matter. Residence time calculations were carried out and validated by tracer studies in a branched network and then in a simply looped network. The measurement of the natural dissolved organic carbon (DOC) consumption in the network was preferred to the determination of any in vitro biodegradation. The measurement of consumption requires the determination of DOC in treated water and in supply water. It is simpler and less expensive than other biodegradable organic matter determinations. A model for colony counts as a function of the residence time was developed in order to demonstrate that this parameter can be used for process controlling. This model was very well adjusted to data collected in a network in winter, spring and summer. This process control parameter was then used in order to locate and estimate the quantity of water whose colony counts exceed the European directive guide level.Accurate correlation measurements between colony counts and DOC consumed in the network were carried out in three distinct systems. No significant correlations were measured. For these three networks, biodegradable organic matter measurements based on DOC determinations were demonstrated to be unreliable process control parameters for monitoring bacterial regrowth

Delta multicopy integration for improved β-galactosidase production in recombinant Saccharomyces cerevisiae

The β-galactosidase industrial production is hampered by the high costs associated with its production and purification. One way to improve the overall productivity of galactosidase β-galactosidase fermentation system would be to use continuous high-cell-density systems. Among these, the ones that use flocculent cells are surely attractive due to its simplicity and low cost. We have previously reported the construction of a flocculent Saccharomyces cerevisiae strain secreting high levels of Aspergillus niger β-galactosidase. Due to the cell flocculation characteristics, the recombinant yeast may be used in a high-cell-density system operating in continuous mode. However, when operating at high dilution rates we have observed some plasmid instability which led to a decrease in the β-galactosidase production. With this work we aim at obtaining stable yeast transformants with at least the same β-galactosidase production level of the previously constructed strain1'1 (construction based on an epissomal plasmid) but with enhanced stability which would allow to increase the enzyme productivity in the continuous system. For that, the lacA gene from A. niger (coding to β-galactosidase) was integrated into the genome of the flocculent yeasts S. cerevisiae NCYC 869 and S. cerevisiae NCYC 869-A3 (ura) using integrative vectors with a G418 and ura3 marker, respectively. The repeated cromossomal δ sequences of the yeasts were employed as target sites for the integration. The S. cerevisiae NCYC 869 integrants were selected by resistance to the aminoglycoside G418 (0.2-1.5 g/I) while for the auxothrophic strain S. cerevisiae NCYC869-A3 the selection of integrants was made on minimal medium. Some transforming colonies that presented a deep blue tonality (due to the presence of the X-gal in the plates of selective medium) were randomly selected for growth in nonselective liquid media containing lactose or glucose. Different levels of β-galactosidase expression were observed independently of the selection marker used. For ones that presented more enzyme activity, expression levels of β-galactosidase, cell growth and substrate consumption were found to be similar with the previous y constructed strain (with a 2μ-based plasmid). Unexpectedly, the flocculation of the original strains was affected by the integration. The most flocculants were from transformation using the ura3 marker selection system and the second ones were from transformation using 1.5 g/I G418 as selective marker. Nevertheless, all transformants were less flocculent when compare with the original strain. Transformants genetic characterization by Southern analysis confirmed the multicopy tandem integration pattern. For the analysed transformants, one or two different integration sites were observed. For the most promising transformants, physiological and genetic characterization is being conducted in order to select for a new recombinant strain to be used in a continuous high-cell-density β-galactosidase producing system

Differences in the flocculation mechanism of Kluyveromyces marxianus and Saccharomyces cerevisiae

A study of the flocculation mechanism of aKluyveromyces marxianus strain, as compared with a strain ofSaccharomyces cerevisiae, is described. The involvement of cell wall proteins in the yeast's flocculation mechanism was studied by methyl-esterification or pepsin or acid phosphatase incubation of the cells. The influence of several ions on the flocculation mechanism was assayed. The obtained results indicated that the structure and/or the spatial arrangement of the cell wall groups involved in flocculation are not the same inK. marxianus as inS. cerevisiae