We compared pyrosequencing technology with the PCR-ITS-RFLP analysis of yeast isolates and denaturing gradient gel electrophoresis (DGGE). These methods gave divergent findings for the yeast population. DGGE was unsuitable for the quantification of biodiversity and its use for species detection was limited by the initial abundance of each species. The isolates identified by PCR-ITSRFLP were not fully representative of the true population. For population dynamics, high-throughput sequencing technology yielded results differing in some respects from those obtained with other approaches. This study demonstrates that 454 pyrosequencing of amplicons is more relevant than other methods for studying the yeast community on grapes and during alcoholic fermentation. Indeed, this high-throughput sequencing method detected larger numbers of species on grapes and identified species present during alcoholic fermentation that were undetectable with the other techniques.

As a complex microbial ecosystem, wine is a particularly interesting model for studying interactions between microorganisms as fermentation can be done by microbial consortia, a unique strain or mixed culture. The effect of a specific yeast strain on its environments is unique and characterized by its metabolites and their concentration. With its great resolution and excellent mass accuracy, ultrahigh resolution mass spectrometry (uHRMS) is the perfect tool to analyze the yeast metabolome at the end of alcoholic fermentation. this work reports the change in wine chemical composition from pure and mixed culture fermentation with Lachancea thermotolerans, Starmerella bacillaris, Metschnikowia pulcherrima and S. cerevisiae. We could clearly differentiate wines according to the yeast strain used in single cultures and markers, which reflect important differences between the yeast species, were extracted and annotated. Moreover, uHRMS revealed underlining intra species metabolomics differences, showing differences at the strain level between the two Starmerella bacillaris. non volatile metabolomics analysis of single and sequential fermentations confirmed that mixed fermentations lead to a different composition. Distinct metabolites appeared in wines from sequential fermentation compared to single fermentation. this suggests that interactions between yeasts are not neutral.Microorganisms coexist in most environments and interact with each other. These interactions happen in nearly every niche on the planet and in numerous processes such as bioremediation of pollutants, farming, biotechnology, medicine or food-processing 1,2 . Under oenological conditions, when yeasts grow simultaneously during alcoholic fermentation, they often do not coexist passively, and in most cases, physiological and metabolic interactions are established between them. The interactions between the different strains of Saccharomyces and non-Saccharomyces yeast can be direct or indirect, through the physicochemical changes in the environment caused by one strain reacting to the other. In oenology, the effect of these interactions is characterized as being positive, negative or neutral 3 . Genomics and proteomics provide an understanding of the interaction 3-5 but none of them could yet provide significant progress on the microbial interaction mechanisms. Recently, high resolution mass spectrometry has been used to elucidate interactions between yeasts and bacteria in the malolactic fermentation by comparison of extracellular metabolic profiles 6 . Even more recently, ultrahigh resolution mass spectrometry (uHRMS) confirmed that cell-cell contact influences the metabolism of L. thermotolerans and S. cerevisiae 7 . Therefore, metabolomics seems to be a suitable tool to better understand the microbial interactome in order to control fermentation by multi-starters. Metabolomics is defined as the study of all metabolites given in a biological system under particular physiological conditions 8 . The analytical techniques developed for metabolomics studi...

cMalolactic fermentation in wine is often carried out by Oenococcus oeni. Wine is a stressful environment for bacteria because ethanol is a toxic compound that impairs the integrity of bacterial membranes. The small heat shock protein (sHsp) Lo18 is an essential actor of the stress response in O. oeni. Lo18 prevents the thermal aggregation of proteins and plays a crucial role in membrane quality control. Here, we investigated the interaction between Lo18 and four types of liposomes: one was prepared from O. oeni grown under optimal growth conditions (here, control liposomes), one was prepared from O. oeni grown in the presence of 8% ethanol (here, ethanol liposomes), one was prepared from synthetic phospholipids, and one was prepared from phospholipids from Bacillus subtilis or Lactococcus lactis. We observed the strongest interaction between Lo18 and control liposomes. The lipid binding activity of Lo18 required the dissociation of oligomeric structures into dimers. Protein protection experiments carried out in the presence of the liposomes from O. oeni suggested that Lo18 had a higher affinity for control liposomes than for a model protein. In anisotropy experiments, we mimicked ethanol action by temperature-dependent fluidization of the liposomes. Results suggest that the principal determinant of Lo18-membrane interaction is lipid bilayer phase behavior rather than phospholipid composition. We suggest a model to describe the ethanol adaptation of O. oeni. This model highlights the dual role of Lo18 in the protection of proteins from aggregation and membrane stabilization and suggests how modifications of phospholipid content may be a key factor determining the balance between these two functions.