Two different Oenococcus oeni lineages are associated to either red or white wines in Burgundy: genomics and metabolomics insights

Oenococcus oeni is the bacterium most often associated with spontaneous malolactic fermentation (MLF) of wine. During MLF, malic acid is transformed into lactic acid and several metabolites are modified, modulating wine’s total acidity and improving its sensory properties. Previous works have suggested that certain genetic groups of O. oeni strains are associated to different kinds of products. In the present study we have spotted two groups of strains isolated mainly from Burgundy wines, one associated to red wines and the other to white wines. Sequencing 14 genomes of red and white wine strains revealed that they share a common ancestor that probably colonised two different substrates –red and white wine-associated environments–, diverging over time and disseminating to various regions. Their capacity to perform MLF and modify the volatile profile of wine was determined by fermenting a chardonnay wine and analysing its volatile fraction with a non-targeted metabolomics approach by GC-MS. The strains had a different impact on the volatile composition depending on their group of origin. These results show for the first time a correspondence between the product of origin of the strains and the volatile profile of the wines they produce. Furthermore, the genetic features that might be implied in these different phenotypes are examined

Front Microbiol

Brettanomyces bruxellensis is the main spoilage microbial agent in red wines. The use of fungal chitosan has been authorized since 2009 as a curative treatment to eliminate this yeast in conventional wines and in 2018 in organic wines. As this species is known to exhibit great genetic and phenotypic diversity, we examined whether all the strains responded the same way to chitosan treatment. A collection of 53 strains of was used. In the conditions of the reference test, all were at least temporarily affected by the addition of chitosan to wine, with significant decrease of cultivable population. Some (41%) were very sensitive and no cultivable yeast was detected in wine or lees after 3 days of treatment, while others (13%) were tolerant and, after a slight drop in cultivability, resumed growth between 3 and 10 days and remained able to produce spoilage compounds. There were also many strains with intermediate behavior. The strain behavior was only partially linked to the strain genetic group. This behavior was little modulated by the physiological state of the strain or the dose of chitosan used (within the limits of the authorized doses). On the other hand, for a given strain, the sensitivity to chitosan treatment was modulated by the chitosan used and by the properties of the wine in which the treatment was carried out.Recherches sur l’origine et les effets secondaires des propriétés stabilisantes du chitosane fongique dans le vi

Reliability of MALDI-TOF mass spectrometry to identify oral isolates of Streptococcus salivarius and Lactobacillus spp

Objective: The aim of this study is to evaluate the performance of MALDI-TOF mass spectrometry in identifying bacteria isolated in the oral cavity known to be of probiotic interest. Design: We evaluated Bruker MALDI Biotyper for the identification of 92 clinical oral isolates of probiotic interest (31 Streptococcus salivarius and 61 Lactobacillus spp.) by comparing direct colony method with on-plate formic acid extraction. Isolates were previously identified by use of biochemical methods and molecular biology. Results: Using the manufacturer's suggested genus and species level cutoff scores, the direct colony method identified 42 (45.7%) isolates at the genus level and 35 (38%) at the species level while the on-plate extraction method correctly identified 90 (97.8%) isolates at the genus level and 82 (89.1%) at the species level. The difference between the two methods was statistically significant at the genus and species levels (P ≤ 0.0001). After dividing the isolates into two subgroups, the analysis was repeated. The direct colony method identified correctly all isolates of Streptococcus salivarius at the species level. In contrast, the direct colony method allowed the identification of only 11 (18%) lactobacilli at the genus level and 4 (6.6%) at the species level. The on-plate extraction method was statistically (P ? 0.0001) more efficient since 59 (96.7%) lactobacilli were identified at the genus level and 51 (83.6%) at the species level. Conclusions: MALDI Biotyper can efficiently identify Streptococcus salivarius regardless of the preparative method but on-plate extraction is superior to direct colony method for the identification of lactobacilli

Grape berry bacterial inhibition by different copper fungicides

Copper fungicides are widely used in viticulture. Due to its large spectrum of action, copper provides an efficient control over a great number of vine pathogens. Previous studies showed that, high levels of cupric residues can impact grape-berry microbiota, in terms of the size and population structure, reducing the diversity and the abundance. Due to the importance of grape-berry bacterial in crop health, and the potential impact of copper fungicides over the microbiota, we determined Minimum Inhibitory Concentration (MIC) of different copper formulations for bacterial species isolated from grape berries. We study the Minimum Inhibitory Concentration (MIC) of different copper formulations (copper sulphate (CuSO4) pure, Bordeaux mixture (CuSO4 + Ca(OH)2), copper oxide (Cu2O), copper hydroxide (Cu(OH) 2)) over 92 bacterial strains isolated from grape berries in different stages of the ripening process. The results of MIC measurements revealed that the different copper formulations have a variable inhibitory effect and among the different isolates, some species are the most resistant to all copper formulations than others. This study confirm that usage of cupric phytosanitary products should be reasonable independently of the farming system; they also provide evidence of the importance of the choice of which copper formulations are to be used regarding their impact on the grape berry bacterial microbiota

Influence of must yeast-assimilable nitrogen content on fruity aroma variation during malolactic fermentation in red wine

International audienceThis study assessed the impact of must yeast-assimilable nitrogen (YAN) content and lactic acid bacteria (LAB) strains used for malolactic fermentation (MLF) on the formation of substituted esters, as well as the corresponding precursors (substituted acids), to investigate the modulation of fruity expression in red wines. In microvinification experiments, a Merlot must was fermented with an initial YAN content of 111 mg/L, or supplemented up to 165 and 220 mg/L. Two Oenococcus oeni LAB strains were used for MLF. Analytical methods were used to quantify substituted esters, as well as the corresponding acids, including, any enantiomeric forms. YAN supplementation of the must significantly increased concentrations of substituted esters of short- and branched-chain alkyl fatty acids produced during alcoholic fermentation (AF) (up to 67% in samples with the highest nitrogen content) and substituted esters of hydroxycarboxylic acids generated during MLF (up to 58% in samples with the highest nitrogen content). YAN supplementation in the must did not affect substituted acid formation during AF. After MLF, short- and branched-chain alkyl fatty acid levels increased in wines made from musts with the highest nitrogen content (up to 56% in samples with the highest nitrogen content), whereas concentrations of hydroxycarboxylic acids increased (up to 55%) independently of the initial YAN content, highlighting the important role of MLF. (2S)-2-hydroxy-4-methylpentanoic acid was only found in wines after malolactic fermentation, suggesting different pathways for each enantiomer and opening up new prospects for the study of bacterial metabolisms. Moreover, sensory profiles revealed a significant increase in black-berry- and jammy-fruit aromas during MLF and a strong positive correlation between these aromas and the production of substituted esters following must nitrogen supplementation and MLF. Aromatic reconstitution revealed that variations in the concentrations of substituted esters after MLF impacted the fruity aroma of red wines

Etude de l'écosystème microbien présent à la surface des barriques utilisées lors de la vinification

National audienceThe microbial community on the surface of wood barrels used in winemaking was determined just before their first use, during first contact with wine, and some months after wine contact during successive racking at different steps of wine elaboration. Five microbial populations (total yeast, non-Saccharomyces yeast, lactic acid bacteria, acetic acid bacteria, and anaerobic and anaerobic tolerant Gram negative bacteria) were identified using 5 different selective culture media. Among each population, species and strains were identified using molecular tools such as the polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis, PCR-restriction fragment length polymorphism and pulsed field gel electrophoresis. At the laboratory scale, the risks of contamination were evaluated by wine inoculation trials and their impact on wine microbial population and chemical properties (volatile phenols and acetic acid) was determined. Before the first use and during the first wine contact, the microbial community on the barrel wood was mainly composed of basidiomycetes (Cryptococcus, Bulleromyces and Rhodotorula) and enterobacteria (Serratia sp. and Shigella sp.). After wine contact, these microorganisms became less and less detectable, which could be explained by their low ethanol resistance. However, some species could resist ethanol and remain detectable some weeks after the first barrelling. The ability of these species to degrade some wood components could affect the wine microbial consortium. In addition, since the first racking, the majority of microbial species found on the wood barrel surface was composed of major wine yeast (Saccharomyces cerevisiae) and bacterial (Oenococcus oeni) species, as well as spoilage organisms such as Brettanomyces bruxellensis, Pediococcus parvulus and Gluconobacter oxydans. Laboratory trials of contamination suggested that these residual populations were unable to cause wine alteration such as volatile phenol and acetic acid production. The microorganisms present on the wood surface could not modify the microbial steady state of wine containing some populations regulated by oenological practices (sulfating, racking) and also by microbial interactions between each species. When the microbial population was low as in the case after filtration or heat treatment, the contamination was more possible. In any cases, washing of barrels at each racking is strongly recommended to progressively eliminate the microorganisms that are adhered to the wood and to obtain an efficient microbial stability of the wine

Wine yeast species show strong inter- and intra-specific variability in their sensitivity to ultraviolet radiation

While the trend in winemaking is toward reducing the inputs and especially sulphites utilization, emerging technologies for the preservation of wine is a relevant topic for the industry. Amongst yeast spoilage in wine, Brettanomyces bruxellensis is undoubtedly the most feared. In this study, UV-C treatment is investigated. This non-thermal technique is widely used for food preservation. A first approach was conducted using a drop-platted system to compare the sensitivity of various strains to UV-C surface treatment. 147 strains distributed amongst fourteen yeast species related to wine environment were assessed for six UV-C doses. An important variability in UV-C response was observed at the interspecific level. Interestingly, cellar resident species, which are mainly associated with wine spoilage, shows higher sensitivity to UV-C than vineyard-resident species. A focus on B. bruxellensis species with 104 screened strains highlighted an important effect of the UV-C, with intra-specific variation. This intra-specific variation was confirmed on 6 strains in liquid red wine by using a home-made pilot. 6624 J.L?1 was enough for a reduction of 5 log10 of magnitude for 5 upon 6 strains. These results highlight the potential of UV-C utilization against wine yeast spoiler at cellar scale.Approche multi-échelle de l'adaptation de la levure Brettanomyces bruxellensis aux procédés fermentaire

Corrigendum to “A new method for monitoring the extracellular proteolytic activity of wine yeasts during alcoholic fermentation of grape must” [J. Microbiol. Methods 119 (2015) 176–179]

Corrigendum to “A new method for monitoring the extracellular proteolytic activity of wine yeasts during alcoholic fermentation of grape must” [J. Microbiol. Methods 119 (2015) 176–179

J Microbiol Methods

The existing methods for testing proteolytic activity are time consuming, quite difficult to perform, and do not allow real-time monitoring. Proteases have attracted considerable interest in winemaking and some yeast species naturally present in grape must, such as Metschnikowia pulcherrima, are capable of expressing this activity. In this study, a new test is proposed for measuring proteolytic activity directly in fermenting grape must, using azocasein, a chromogenic substrate. Several yeast strains were tested and differences in proteolytic activity were observed. Moreover, analysis of grape must proteins in wines revealed that protease secreted by Metschnikowia strains may be active against wine proteins