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The aviation industry considers the development of sustainable biofuels as one of the biggest challenges of the next ten years. The aim is to lower the environmental impact of the steadily increasing use of fossil fuels on climate change, yielding greater energy independence and fuel security. Thus, the development of a new route for the production of lipids from renewable non-food resources is now being promoted with the recent ASTM certification of hydrotreated oils. Our study focuses on the potential of growth of the oleaginous yeast Rhodotorula glutinis using glucose and xylose which can come from renewable lignocellulosic substrates and of lipid accumulation using glucose as substrate. Experiments were carried out in fed-batch mode which allowed feed flux management. Carbon fluxes were controlled with modifying xylose/glucose ratios to quantify metabolism in optimal growth condition. Besides, the management of carbon and nitrogen fluxes allowed characterizing lipid accumulation. Thus, it has been shown that the yeast Rhodotorula glutinis can simultaneously consume glucose and xylose. When the ratio xylose/glucose increased, the growth rate and the carbon conversion yield into biomass decreased: it was of 0.36 h-1 and 0.64 Cmol x*.Cmol glu-1 for pure glucose, it was of 0.15 h-1 and 0.56 Cmol.Cmol-1 for 10% xylose and it was of 0.037 h-1 and 0.18 Cmol.Cmol-1 for pure xylose. The necessity to maintain residual growth and to manage carbon fluxes to optimize lipid accumulation performance was revealed. Lipid accumulation on glucose engendered a final biomass concentration of 150 gCDW.L-1, microbial production (72% of lipids) and maximal productivity over 1.48 glip.L-1.h-1. The culture temperature is an important parameter to modulate the lipid profile. The results were encouraging. Lipid accumulation using lignocellulosic feedstock was shown to be a highly promising route. Le développement de filières de production de molécules énergétiques en substitution au kérosène constitue un défi majeur pour l’industrie aéronautique afin de minimiser l’impact environnemental de son activité et de répondre à ses besoins en énergie, dont la demande est croissante. Le développement d’une nouvelle voie de production de lipides à partir de ressources renouvelables non alimentaires ouvre des perspectives prometteuses avec la certification ASTM des huiles hydrotraitées. Les travaux expérimentaux consistent en l’étude, d’une part, des potentialités de croissance de la levure oléagineuse Rhodotorula glutinis à partir de glucose et/ou xylose, substrats osidiques issus des ressources lignocellulosiques, et d’autre part, des potentialités d’accumulation de lipides à partir de glucose. Des cultures en mode fed-batch ont permis le contrôle des flux d’alimentation : en carbone, en condition de croissance, selon un ratio xylose/glucose variable pour la quantification du métabolisme, et en azote, en condition de production de lipides. Il a été montré que la levure Rhodotorula glutinis est capable de consommer simultanément le glucose et le xylose. Le taux de croissance et le rendement de conversion du carbone en biomasse diminuent en fonction de la composition du mélange xylose/glucose : à savoir 0,36 h-1 et 0,43 Cmol. x*.Cmol glu-1 sur glucose pur, 0,15 h-1 et 0,56 Cmol.Cmol-1 sur 10 % de xylose, 0,037 h-1 et 0,18 Cmol.Cmol-1 sur xylose pur. Par ailleurs, lors d’expérimentation en condition. d’accumulation lipidique, il a été mis en évidence la nécessité de maintenir une croissance résiduelle par le contrôle des flux d’azote et de carbone. Lors de la phase de production de lipides sur glucose, il a été ainsi obtenu une concentration finale en biomasse de 150 gCDW.L-1 contenant 72 % de lipides en masse; la productivité volumétrique maximale atteint 1,5 glip.L-1.h-1, avec un rendement de conversion du glucose en lipides égal à 95 % du rendement théorique limite La température de culture se révèle un paramètre opératoire important pour la modulation du profil lipidique. Ces résultats sont originaux et ils ont permis l’obtention de très hautes performances, en culture intensive. Ils argumentent des potentialités de développement d’une stratégie de production de lipides par conversion de toutes les fractions osidiques des substrats lignocellulosiques pour des usages biokérosène après hydrotraitement.

Heterogeneities caused by deficient mixing in large-scale bioreactors have been identified and described in literature. These heterogeneities affect physiological changes of microorganisms through its passage in different zones of concentrations. Consequently the differences in terms of productivities, qualities and/or yields of products of interest have been observed during scaling-up from laboratory to larger scales. For this reason, large-scale process improvement depends on the understanding of dynamic interactions between microbial responses and physical phenomena inside bioreactors. The dynamic responses of microorganisms are used as a tool for gaining insight into the fundamentals of microbial changes under a mixing-well controlled environment. Our research group has not only applied scale-down methodology to study the microbial responses at molecular, microscopic and macroscopic levels of observation, but also has used innovative strains and process engineering tools to evaluate fast dynamic responses of microorganism at time scales from seconds to minutes. This presentation focuses on the application of rational strategies in order to characterize distributed relaxation times of microorganisms which are considered to be constant at all fermentation scales. Experiments were conducted with reporter bioluminescent strains of Escherichia coli in which the luxCDABE operon was fused to promoters responding to different selected environmental stresses (dissolved oxygen, pH, temperature and substrate, etc.). Such strains allow real-time recording of the expression of genes involved in stress responses. Kinetic analyses of biomass, extracellular metabolites, inlet/exhaust gas, were carried out in order to determine mass balances and biological kinetic parameters. We will present our approach and the results concerning continuous culture of E. coli DPD2417 (nirB::luxCDABE) to monitor the microbial responses to oxygen limitation.

Recent data have advanced our understanding of the mechanism which underlies the periodicity of somitogenesis. The observation that avian c-hairy1 (1) and avian (2) and murine (3) lunatic fringe RNA levels cycle in the presomitic mesoderm (PSM) supports theoretical models predicting a temporal periodicity derived from an autonomous oscillator within the PSM cells (4). Translation of this temporal periodicity into a spatial periodicity manifest in the somites requires Notch intercellular signalling (5). Moreover, our recent finding that the Notch target gene HES1 cycles in the mouse PSM (6) suggests Notch signalling may also be directly involved in the regulation of murine cycling gene expression We are currently studying isolated PSM cells in culture to assess the role of inter- and intracellular mechanisms in the maintainance of such cyclical gene expression. In addition we are characterising the kinetics of translation of the oscillating genes during somite formation, as well as investigating the role that post-translational modification might play in the mechanism of the putative molecular clock. 1. Palmeirim I. Henrique D. Ish-Horowicz D. & Pourquie O. Cell (1997) 91:639-648;2. McGrew MJ. Dale JK. Fraboulet S. & Pourquie O. Curr. Biol. (1998) 8:979-982;3. Forsberg H. Crozet F. Brown NA. Curr. Biol. (1998) 8:1027-1030;4. Dale KD & Pourquie O. BioEssays (2000) 22:72-83;5. McGrew M. & Pourquie O. Curr. Opin Genet Dev (1998) 8:487-493;6. Jouve C, Palmeirim I, Henrique D, Beckers J, Gossler A, Ish-Horowicz D & Pourquie O;Development(2000)127:1421-29

STUDY DESIGN: This prospective cohort study evaluated four office tests of quadriceps strength in symptomatic adults with radiographic evidence of L3 or L4 nerve root compression. OBJECTIVE: The study observed the performance of each test for its ability to detect quadriceps weakness when compared to the asymptomatic side. To determine the potential influence of radicular pain on the performance of the four tests, a control group of patients over the age of 40 with clinical and radiographic L5 or S1 radiculopathies underwent identical testing of quadriceps strength. SUMMARY OF BACKGROUND DATA: The L3 and L4 nerve roots innervate the quadriceps; therefore, quadriceps weakness may be a consequence of L3 or L4 radiculopathies. There are no standardized or validated methods to evaluate quadriceps strength in the clinical office setting. This may lead to inconsistent detection by clinicians of quadriceps weakness in cases of L3 or L4 radiculopathy. METHODS: Thirty-three consecutive patients with L3 or L4 radiculopathies and 19 with L5 or S1 radiculopathies were studied. The four tests of quadriceps strength included: 1) single leg sit-to-stand test; 2) step-up test; 3) knee-flexed manual muscle testing; and 4) knee-extended manual muscle testing. Results from a second examiner repeating the four tests were used to calculate interrater reliability. RESULTS: In L3 and L4 radiculopathies, unilateral quadriceps weakness was detected by the single leg sit-to-stand test in 61%, by knee-flexed manual muscle testing in 42%, by step-up test in 27% and by knee-extended manual muscle testing in 9% of patients. The sit-to-stand test detected weakness in all but one case when weakness was detected by another test. All patients with L5 or S1 radiculopathies could perform the sit-to-stand test. Kappa coefficient was high for sit-to-stand test (0.85), step-up (0.83), and knee-flexed manual muscle testing (0.66), and low for knee-extended manual muscle testing (0.08). CONCLUSION: In L3 and L4 radiculopathies, unilateral quadriceps weakness was best detected by a single leg sit-to-stand test. Patients of similar age with radicular pain caused by L5 or S1 radiculopathies could perform this test. As the interrater reliability of the single leg sit-to-stand test is high, clinicians should consider utilizing this test for assessing quadriceps strength in cases of L3 and L4 radiculopathies. [ABSTRACT FROM AUTHOR]