Stability and performance of two GSBR operated in alternating anoxic/aerobic or anaerobic/aerobic conditions for nutrient removal

Two granular sludge sequencing batch reactors (GSBR) with alternating anoxic/aerobic (R1) and anaerobic/aerobic (R2) conditions were operated with a 4-carbon-source synthetic influent. The physical properties of the granular sludge were very good (SVI≈20 mL g−1) and high solid concentrations (up to 35 g L−1) were obtained in the bioreactor operated with a pre-anoxic phase with additional nitrate (R1). In contrast, performance and granule settleability were lower in R2 due to the development of filamentous heterotrophic bacteria on the surface of granules. These disturbances were linked to the fact that a fraction of COD remained during the aerobic phase, which was not stored during the anaerobic period. To stabilize a GSBR with a mixture of organic carbon sources, it is thus necessary to maximize the amount of substrate used during the non-aerated, anaerobic or anoxic, phase. Comparable phosphate removal efficiency was observed in both systems; enhanced biological P removal being greater in anaerobic/aerobic conditions, while the contribution of precipitation (Ca–P) was more significant in anoxic/aerobic conditions

Analyse métabolique et énergétique de Lactobacillus bulgaricus sous contrainte d'extrèmophilie industrielle

Le procédé de fabrication du yaourt inflige aux bactéries lactiques une dynamique particulière de stress acide et thermique, qui aboutit à une phase de post-acidification durant laquelle le catabolisme se poursuit alors que la croissance est inhibée. Nos travaux de recherche, en partenariat avec un industriel, ont consisté à caractériser le phénotype et à étudier la régulation du métabolisme central, d'une bactérie lactique d'origine industrielle. Cette approche intègre l'étude du comportement macro- et micro-cinétique, dans le but d'identifier les niveaux de régulation et les mécanismes de contrôle de la glycolyse, en dynamique d'acidification et au cours de la phase de post-acidification. En condition de référence, à pH (6,4) et température (42ʿC) fixes, le profil de croissance de Lactobacillus bulgaricus, en milieu lait ou en milieu synthétique, est atypique, et caractérisé par deux phases de croissance. L'entrée en phase stationnaire transitoire est provoquée par l'accumulation de composés toxiques synthétisés durant la première phase de croissance. La croissance est limitée au niveau de l'anabolisme, et le flux catabolique est ajusté aux capacités anaboliques. En culture à pH libre, la baisse du pH inhibe les enzymes glycolytiques, et provoque un ralentissement du flux glycolytique de production d'énergie. Au pH interne de 4,7, la disponibilité en énergie devient insuffisante pour permettre la croissance. Lors de la dynamique d'apparition des stress acide et hypothermique au cours du procédé, c'est-à-dire en culture à pH libre et avec transferts de température, l'effet de la baisse de température inhibe la croissance à un pH modéré, qui permet au catabolisme de se poursuivre pendant des jours, jusqu'à ce qu'un pH interne de 4,7 soit atteint. D'après l'analyse physiologique globale, comme chez Lactococcus lactis, le contrôle de la glycolyse s'effectue principalement au niveau de la glycéraldéhyde 3-phosphate déshydrogénase en phase de croissance et de la phosphofructokinase en phase stationnaire, à pH régulé comme à pH libre à 42ʿC. Ces résultats permettent d'identifier les cibles d'action à privilégier dans le but de maîtriser la phase de post-acidificationTOULOUSE-INSA (315552106) / SudocSudocFranceF

Metabolism of Lactococcus lactis subsp. cremoris MG 1363 in acid stress conditions

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Transient self-inhibition of the growth of Lactobacillus delbrueckii subsp. bulgaricus in a pH-regulated fermentor

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Energetic analysis of cultures of Lactobacillus delbrueckii subsp. bulgaricus: identification of the type of control between catabolism and anabolism

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A Unique Phenotypic Modification of Lactococcus lactis Cultivated in a Couette Bioreactor

International audienceBatch cultures of Lactococcus lactis NCDO 2118 and IL 1403 were performed in a Couette bioreactor operated in the modulated wavy vortex flow and the turbulent regimes. This study provides an overall analysis taking into account both mechanical stress and mixing in a Couette bioreactor. A unique phenotypic aspect has been proved to occur only in the modulated wavy vortex flow regime for the two studied strains, namely that the cells become entrapped in a filamentous form. No change in the metabolic behavior of the cells has been observed. The polymeric matrix has been microscopically observed through FISH and fluorescent lectin binding, showing cells entrapped in a glycoconjugate matrix. All hypotheses regarding insufficient mixing as a cause of this phenotype have been discarded, leading to the conclusion that this particular phenotypic feature is essentially due a combined effect of mechanical stress and flow structure. Particle size measurement during the fermentation course indicates that formation of filamentous form results from a continuous aggregation started in the early stages of the cultivation. According to our results a minimum shear is required to induce the ability for cells to aggregate. Then, it appears that both flow structure and mechanical stress (shear) are responsible for the appearance of such a filamentous form. As far as the authors know, this is the first experimental evidence of a bio polymerization induced by the flow structure. Biotechnol. Bioeng. 2011;108: 559-571. (C) 2010 Wiley Periodicals, Inc

Regulation of glycolysis of Lactococcus lactis ssp. cremoris MG 1363 at acidic culture conditions

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Transcriptome Analysis of Lactococcus lactis in Coculture with Saccharomyces cerevisiae▿

The study of microbial interactions in mixed cultures remains an important conceptual and methodological challenge for which transcriptome analysis could prove to be the essential method for improving our understanding. However, the use of whole-genome DNA chips is often restricted to the pure culture of the species for which the chips were designed. In this study, massive cross-hybridization was observed between the foreign cDNA and the specific Lactococcus lactis DNA chip. A very simple method is proposed to considerably decrease this nonspecific hybridization, consisting of adding the microbial partner's DNA. A correlation was established between the resulting cross-hybridization and the phylogenetic distance between the microbial partners. The response of L. lactis to the presence of Saccharomyces cerevisiae was analyzed during the exponential growth phase in fermentors under defined growth conditions. Although no differences between growth kinetics were observed for the pure and the mixed cultures of L. lactis, the mRNA levels of 158 genes were significantly modified. More particularly, a strong reorientation of pyrimidine metabolism was observed when L. lactis was grown in mixed cultures. These changes in transcript abundance were demonstrated to be regulated by the ethanol produced by the yeast and were confirmed by an independent method (quantitative reverse transcription-PCR)