Search results for "Coccus"
showing 10 items of 1002 documents
Modification de la composition lipidique membranaire chez les bactéries lactiques en conditions de stress : étude du rôle physiologique des Acides Gr…
2010
The results obtained in this work have shown that in both lactic acid bacteria models, L. lactis subsp. cremoris and O. oeni, transcription of the cfa gene, encoding the Cfa synthase is stimulated when cells enter stationary phase of growth or when the cells are grown under stress conditions (acidic or presence of ethanol in the medium). The role of the CFAs has been apprehended by the comparative physiological analysis of the parental strain L. lactis subsp. cremoris and a Δcfa mutant generated in this strain. The high percentages of survival obtained in strains grown at pH 5.0 and undergoing acid stress (pH 3.0) prove that the cyclopropanation of unsaturated fatty acids is not essential t…
Use of antisense RNA to modulate HSP gene expression in oenococcus oeni
2015
International audience
Improving acid tolerance in Oenococcus oeni by Adaptive Evolution
2017
International audience; Oenococcus oeni is a lactic acid bacterium (LAB) mainly responsible for the malolactic fermentation (MLF) inwine. MLF plays an important role in determining the final quality of wines[1]. Even though this LAB is naturally present in musts, wines and oenological environment, spontaneous MLF are usually unpredictable because of the stressful conditions and especially due to acidity [2]. The consequence of the mismanagement ofthis step might lead to the depreciation of wine quality. To obtain a clone more tolerant to acidity, we undertaken to replicate O. oeni in a temporally varying environment (pH 5.3 to 3.2) to improve acid tolerance. To discriminate stress tolerance…
Adaptive evolution to improve acid tolerance in Oenococcus oeni
2019
International audience; Oenococcus oeni is a lactic acid bacterium (LAB) mainly responsible for the malolactic fermentation (MLF) inwine. MLF plays an important role in determining the final quality of wines [1]. Even though this LAB is naturallypresent in musts, wines and oenological environment, spontaneous MLF are usually unpredictable because of thestressful conditions and especially due to acidity [2]. The consequence of the mismanagement of this step might leadto the depreciation of wine quality. To obtain a clone more tolerant to acidity, we undertook a replication of O. oeni until 450 generations in a temporally varying environment (pH 5.3 to 2.9) to improve acid tolerance. To discr…
Oenococcus oeni : advances in molecular genetics
2017
International audience
Study of biogenic amines metabolism in wine lactic acid bacteria
2011
Biogenic amines are indesirable compounds found in fermented products like wine. Lactic acid bacteria from wine, including Oenococcus oeni, the main actor of malolactic fermentation, are able to produce these molecules from nitrogenous precursors. In order to limited biogenic amines accumulation, it is necessary to understand the role of this production by strains responsible for the synthesis of these metabolites in food. That is why the European BiamFood project was put in place. Along my thesis, molecular tools were developed in order to mutate O. oeni genes (encoding decarboxylases), and to express genes of interest. Genetic clusters hdc from L. higardii and odc from O. oeni, responsibl…
Effect of oxidoreduction potential on aroma biosynthesis by lactic acid bacteria in nonfat yogurt
2011
; The aim of this study was to investigate the effect of oxidoreduction potential (Eh) on the biosynthesis of aroma compounds by lactic acid bacteria in non-fat yogurt. The study was done with yogurts fermented by Lactobacillus bulgaricus and Streptococcus thermophilus. The Eh was modified by the application of different gaseous conditions (air, nitrogen, and nitrogen/hydrogen). Acetaldehyde, dimethyl sulfide, diacetyl, and pentane-2,3-dione, as the major endogenous odorant compounds of yogurt, were chosen as tracers for the biosynthesis of aroma compounds by lactic acid bacteria. Oxidative conditions favored the production of acetaldehyde, dimethyl sulfide, and diketones (diacetyl and pen…
Inactivation of lactococcal aromatic aminotransferase prevents the formation of flora aroma compounds from aromatic amino acids in semi-hard cheese
1999
The enzymatic conversion of aromatic amino acids to aroma compounds plays a role in the formation of an undesirable floral aroma in Cheddar-like cheeses. In lactococci, the first step of aromatic amino acid degradation is a transamination, catalysed by an aromatic aminotransferase (AraT). We observed previously that in vitro, araT inactivation prevented degradation of aromatic amino acids and decreased degradation of Met and Leu. In this study we evaluated the effect of araT inactivation in Lactococcus lactis on flavour development in St. Paulin-type cheese. The degradation of amino acids was monitored by using radiolabelled amino acids and the volatile compounds formed were analysed by GC-…
Amino acids role in biogenic amine production by Oenococcus Oeni
2013
In wine biogenic amines (BA) are mainly of microbial origin, Oenococcus oeni, the mainresponsible for malolactic fermentation, has been identified as a BA producer from nitrogenprecursors. Oenococcus oeni possess numerous amino acid auxotrophies that are precursors ofbiogenic amines. No study has been done so far to look at the relationship betweenauxotrophy for amino acids precursors of BA and the level of BA in the medium. In order todo so, 80 Oenococcus oeni strains were isolated from red wines. The detection of genesencoding the different decarboxylases responsible for BA synthesis has been realised. Inparallel, the auxotrophy for the four amino acids (Arg, Tyr, His, Phe) precursors of …
Impact de la modulation de la réponse inflammatoire pulmonaire et systémique de l'hôte mediée par Toll-Like Receptor 2 dans un modèle animal de pneum…
2012
EA MERS Hors CT hors EJ; Master