Lors de ce travail, une étude comparative entre trois souches de C. glutamicum a été réalisée. Celles-ci sont C. glutamicum 2262, une souche surproductrice de glutamate suite à l’élévation de température du milieu de culture de 33 à 39°C, C. glutamicum 2262 NP un variant incapable d’excréter du glutamate dans ces mêmes conditions et C. glutamicum 2262 ∆pks13 un mutant dépourvu de bicouche mycolique externe. Un modèle métabolique original reprenant les différentes modifications physiologiques aboutissant à l’excrétion du glutamate au cours du procédé thermo-induit a été établi. La bicouche mycolique joue un rôle primordial puisque son absence affecte sévèrement la production du glutamate. Dans un premier temps, l’élévation de température serait ressentie au niveau de cette bicouche. Ce ressenti, visualisé par l’accumulation de protéines caractéristiques d’un stress thermique, est nécessaire pour que la bactérie soit en capacité de surproduire le glutamate. Par la suite, la production de glutamate est régulée au niveau de l’α-cétoglutarate déshydrogénase (ODH) grâce à la phosphoprotéine OdhI. Suite au changement de température, celle-ci est déphosphorylée ce qui lui permet d’interagir avec ODH et de provoquer l’inhibition de cette dernière. Ceci se traduit par la redirection sur flux carboné vers la synthèse du glutamate. Aucun de ces évènements n’est observé chez C. glutamicum 2262 ∆pks13. Par ailleurs, l’élévation de température induit une modification de la composition de l’enveloppe cellulaire qui semble intervenir dans le processus physiologique aboutissant à l’excrétion du glutamate puisque très peu de changements sont observés chez C. glutamicum 2262 NP / During this work, a comparative study between three strains of Corynebacterium glutamicum was carried out. These strains were C. glutamicum 2262 which overproduces glutamate after an increase in the culture temperature from 33 to 39°C, C. glutamicum 2262 NP which is unable to produce glutamate in the same culture conditions and C. glutamicum 2262 ∆pks13 devoid of outer corynomycolic acid bilayer. An original metabolic model describing the successive physiological modifications responsible for the glutamate excretion during the temperature-triggered process was established. The presence of the corynomycolic acid bilayer appeared to be necessary since its lack affected dramatically the glutamate production. The temperature increase would be first sensed at the level of the external corynomycolic acid layer. This sensing was visualised through the accumulation of thermal stress proteins. In C. glutamicum 2262 ∆pks13, the synthesis of these proteins was not induced. The glutamate production is regulated at the oxoglutarate dehydrogenase (ODH) level by the phosphoprotein OdhI. A consequence of the temperature increase was the dephosphorylation of this regulatory protein and its interaction with ODH, provoking its inhibition. The carbon flux was then reoriented toward the glutamate synthesis. In C. glutamicum 2262 ∆pks13, no dephosphorylation of OdhI and no change in the ODH activity were not determined. The thermal stress also induced a change in the composition of the corynomycolic acid layer which was correlated with the ability of C. glutamicum 2262 to overproduce glutamate. In C. glutamicum 2262 NP, the composition of the corynomycolic acid layer remained unchanged

Indiana University-Purdue University Indianapolis (IUPUI) / The expression of pyruvate dehydrogenase kinase (PDK) 2 and 4 are increased in the fasted state to inactivate the pyruvate dehydrogenase complex (PDC) by phosphorylation to conserve substrates for glucose production. To assess the importance of PDK2 and PDK4 in regulation of the PDC to maintain glucose homeostasis, PDK2 knockout (KO), PDK4 KO, and PDK2/PDK4 double knockout (DKO) mice were generated. PDK2 deficiency caused higher PDC activity and lower blood glucose levels in the fed state while PDK4 deficiency caused similar effects in the fasting state. DKO intensified these effects in both states. PDK2 deficiency had no effect on glucose tolerance, PDK4 deficiency produced a modest effect, but DKO caused a marked improvement, lowered insulin levels, and increased insulin sensitivity. However, the DKO mice were more sensitive than wild-type mice to long term fasting, succumbing to hypoglycemia, ketoacidosis, and hypothermia. Stable isotope flux analysis indicated that hypoglycemia was due to a reduced rate of gluconeogenesis. We hypothesized that hyperglycemia would be prevented in DKO mice fed a high saturated fat diet for 30 weeks. As expected, DKO mice fed a high fat diet had improved glucose tolerance, decreased adiposity, and were euglycemic due to reduction in the rate of gluconeogenesis. Like chow fed DKO mice, high fat fed DKO mice were unusually sensitive to fasting because of ketoacidosis and hypothermia. PDK deficiency resulted in greater PDC activity which limited the availability of pyruvate for oxaloacetate synthesis. Low oxaloacetate resulted in overproduction of ketone bodies by the liver and inhibition of ketone body and fatty acid oxidation by peripheral tissues, culminating in ketoacidosis and hypothermia. Furthermore, when fed a ketogenic diet consisting of low carbohydrate and high fat, DKO mice also exhibited hypothermia, ketoacidosis, and hypoglycemia. The findings establish that PDK2 is more important in the fed state, PDK4 is more important in the fasted state, survival during long term fasting depends upon regulation of the PDC by both PDK2 and PDK4, and that the PDKs are important for the regulation of glucose and ketone body metabolism.