Laboratoire d'Ingénierie des Systèmes Biologiques et des Procédés

From the perspective of producing P(3HB-co-3HV), the selection of PHA accumulating organisms from activated sludge with a feeding incorporating propionate was investigated in open continuous culture under dual carbon and phosphorus limitation conditions. The selected consortia were then harvested in batch cultures with phosphorus (P) deficiency to evaluate their PHA storage potential. Microbial selection exhibited consistent functional stability of PHA production, emphasizing the robustness of this enrichment strategy. A comparison with previous studies revealed that at a given degree of P limitation, the distribution of carbon consumption between cell growth, PHA storage and maintenance reactions was conditioned by the nature of the carbon source. The combination of the nature of the carbon substrate, the degree of P limitation and the dilution rate governs microbial competition. The dominant bacterial genera showed very heterogeneous PHA production capacities. Acinetobacter spp., whose establishment was favored by the presence of acetate, a high dilution rate, and a low C/P ratio, was found to be a poor producer. In contrast, Malikia spp. and Zoogloea spp., mostly selected with butyrate, a lower dilution rate, and strong P limitation, exhibited high specific PHA production rates.

Le poster a été présenté à l'oral <br/>Le poster a été présenté à l'oral<br/>Le poster a été présenté à l'oral

Optical fiber probe has been recently developed for characterizing the liquid dispersed in gas in droplet form, but its performance has yet been identified for an actual spray system. This work aims to compare the performance of a monofiber optical probe in characterizing the hydrodynamics in spray systems with that of a high-speed camera. Initially, both techniques determined the same series of droplets produced by a syringe. The droplet velocities and sizes obtained from the optical probe were in accordance with the high-speed camera when the droplet coalescence was filtered out from the data. Second, a full-cone spray nozzle was used and the average velocities from the two techniques were close, but the off-center collision on the probe and the difference in size limits caused the discrepancy in the size determination. However, the probe is still beneficial to determine the droplet hydrodynamics and local liquid fraction, the essential characteristics of a spray system.

Phosphoserine aminotransferase (SerC) from Escherichia coli (E. coli) MG1655 is engineered to catalyze the deamination of homoserine to 4-hydroxy-2-ketobutyrate, a key reaction in producing 1,3-propanediol (1,3-PDO) from glucose in a novel glycerol-independent metabolic pathway. To this end, a computation-based rational approach is used to change the substrate specificity of SerC from l-phosphoserine to l-homoserine. In this approach, molecular dynamics simulations and virtual screening are combined to predict mutation sites. The enzyme activity of the best mutant, SerCR42W/R77W , is successfully improved by 4.2-fold in comparison to the wild type when l-homoserine is used as the substrate, while its activity toward the natural substrate l-phosphoserine is completely deactivated. To validate the effects of the mutant on 1,3-PDO production, the "homoserine to 1,3-PDO" pathway is constructed in E. coli by coexpression of SerCR42W/R77W with pyruvate decarboxylase and alcohol dehydrogenase. The resulting mutant strain achieves the production of 3.03 g L-1 1,3-PDO in fed-batch fermentation, which is 13-fold higher than the wild-type strain and represents an important step forward to realize the promise of the glycerol-independent synthetic pathway for 1,3-PDO production from glucose.

Variation in gene expression among genetically identical individual cells (called gene expression noise) directly contributes to phenotypic diversity. Whether such variation can impact genome stability and lead to variation in genotype remains poorly explored. We addressed this question by investigating whether noise in the expression of genes affecting homologous recombination (HR) activity either directly (RAD52) or indirectly (RAD27) confers cell-to-cell heterogeneity in HR rate in Saccharomyces cerevisiae. Using cell sorting to isolate subpopulations with various expression levels, we show that spontaneous HR rate is highly heterogeneous from cell-to-cell in clonal populations depending on the cellular amount of proteins affecting HR activity. Phleomycin-induced HR is even more heterogeneous, showing that RAD27 expression variation strongly affects the rate of recombination from cell-to-cell. Strong variations in HR rate between subpopulations are not correlated to strong changes in cell cycle stage. Moreover, this heterogeneity occurs even when simultaneously sorting cells at equal expression level of another gene involved in DNA damage response (BMH1) that is upregulated by DNA damage, showing that the initiating DNA damage is not responsible for the observed heterogeneity in HR rate. Thus gene expression noise seems mainly responsible for this phenomenon. Finally, HR rate non-linearly scales with Rad27 levels showing that total amount of HR cannot be explained solely by the time- or population-averaged Rad27 expression. Altogether, our data reveal interplay between heterogeneity at the gene expression and genetic levels in the production of phenotypic diversity with evolutionary consequences from microbial to cancer cell populations.

Abstract In this paper, the authors present an alternative methodology to improve (or at least to reduce) the uncertainty level within the prediction of the life time of subsea structures. The focus is made on rigid spool & jumper (or any piping system) prone to internal intermittent multiphase flow (currently named slug flow) and any potential Flow-Induced Vibrations (FIV) phenomenon. As it will be more exhaustively detailed here below, the proposed modelling aims at recovering at the best both (i) the multiphase flow kinematics (i.e. both gas pocket & liquid slug) to be expected in the flow loop and (ii) the resulting loads seen by the structure. The considered multiphase flow solver is based on the well-known Unit Cell Model (UCM, refer to Nicklin et al. (1962), Wallis (1969)) and coupled with usual commercial Finite Element (FE) solvers to recover the expected vibratory levels within the mechanical system. With rigorous purpose, a step-by-step validation process is presented within this paper to progressively validate the different step changes in regard to the current Best Practices (as e.g. reminded by Payne (2015) or Ancian (2016)). Both Computational Fluid Dynamics (CFD) model and experimental database, as extracted from the literature, have been considered to assess the ability of the proposed methodology to recover the expected multiphase flow kinematics and the loads induced by a Taylor bubble flowing within a rigid spool. Once validated, the multiphase flow solver has been coupled to a Finite Element (FE) model to properly assess the Flow-Induced Vibrations (FIV) of the spool resulting from such intermittent slugging solicitations. As here below underlined, the presented comparisons with the Industry Standards suggest (i) the need to challenge the recommended practices to ensure safe and reliable design and (ii) to properly manage the safety Design Fatigue Factor (DFF) to be considered within engineering phases.