12 research outputs found

    Understanding Wine through Yeast Interactions

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    Wine is a product of microbial activities and microbe–microbe interactions. Yeasts are the principal microorganisms responsible for the evolution and fulfillment of alcoholic fermentation. Several species and strains coexist and interact with their environment and with each other during the fermentation course. Yeast–yeast interactions occur even from the early stages of fermentation, determining yeast community structure and dynamics during the process. Different types of microbial interactions (e.g., mutualism and commensalism or competition and amensalism) may exert positive or negative effects, respectively, on yeast populations. Interactions are intimately linked to yeast metabolic activities that influence the wine analytical profile and shape the wine character. In this context, much attention has been given during the last years to the interactions between Saccharomyces cerevisiae (SC) and non-Saccharomyces (NS) yeast species with respect to their metabolic contribution to wine quality. Yet, there is still a significant lack of knowledge on the interaction mechanisms modulating yeast behavior during mixed culture fermentation, while much less is known about the interactions between the various NS species or between SC and Saccharomyces non-cerevisiae (SNC) yeasts. There is still much to learn about their metabolic footprints and the genetic mechanisms that alter yeast community equilibrium in favor of one species or another. Gaining deeper insights on yeast interactions in the grape–wine ecosystem sets the grounds for understanding the rules underlying the function of the wine microbial system and provides means to better control and improve oenological practices

    Highly Invasive Listeria monocytogenes Strains Have Growth and Invasion Advantages in Strain Competition.

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    Multiple Listeria monocytogenes strains can be present in the same food sample; moreover, infection with more than one L. monocytogenes strain can also occur. In this study we investigated the impact of strain competition on the growth and in vitro virulence potential of L. monocytogenes. We identified two strong competitor strains, whose growth was not (or only slightly) influenced by the presence of other strains and two weak competitor strains, which were outcompeted by other strains. Cell contact was essential for growth inhibition. In vitro virulence assays using human intestinal epithelial Caco2 cells showed a correlation between the invasion efficiency and growth inhibition: the strong growth competitor strains showed high invasiveness. Moreover, invasion efficiency of the highly invasive strain was further increased in certain combinations by the presence of a low invasive strain. In all tested combinations, the less invasive strain was outcompeted by the higher invasive strain. Studying the effect of cell contact on in vitro virulence competition revealed a complex pattern in which the observed effects depended only partially on cell-contact suggesting that competition occurs at two different levels: i) during co-cultivation prior to infection, which might influence the expression of virulence factors, and ii) during infection, when bacterial cells compete for the host cell. In conclusion, we show that growth of L. monocytogenes can be inhibited by strains of the same species leading potentially to biased recovery during enrichment procedures. Furthermore, the presence of more than one L. monocytogenes strain in food can lead to increased infection rates due to synergistic effects on the virulence potential

    Cell-contact dependent growth competition of <i>L</i>. <i>monocytogenes</i> strains.

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    <p><i>L</i>. <i>monocytogenes</i> strains (A) PL25-Rif<sup>R</sup> and (B) ScottA-Str<sup>R</sup> were grown alone (single), mixed (contact) and in the presence of the second <i>L</i>. <i>monocytogenes</i> strain separated by a 0.4 μm membrane (no-contact) in TSB-Y for 10 days at 10°C. Data represented as log (CFU/ml) are mean values ± standard deviation of three biological replicates performed in duplicate. Different letters indicate statistically significant differences between single culture, contact and non-contact co-cultivation at the different time points (P<0.05).</p

    Cell-contact-dependent virulence competition of <i>L</i>. <i>monocytogenes</i> strains.

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    <p>(A&B) Invasion efficiency (%) and (C&D) intracellular growth (IGC) were determined for PL25-Rif<sup>R</sup> and ScottA-Str<sup>R</sup> using i) single cultures, ii) mixed culture (strains in contact during growth and infection assay), iii) co-culture without cell-contact (strains grown together separated by the membrane) and used singly for the virulence assay and iv) co-culture without cell-contact (strains grown together separated by the membrane), and in contact during virulence assay. Data, represented as % of invasion and IGC, are mean values ± standard deviation of three biological replicates performed in triplicate. Different letters indicate statistically significant differences between the conditions (P<0.05). P-values are shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0141617#pone.0141617.s005" target="_blank">S4 Table</a>.</p

    Effect of strain competition on the invasion efficiency of <i>L</i>. <i>monocytogenes</i> strains.

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    <p>Invasion efficiency (%) of <i>L</i>. <i>monocytogenes</i> strains (A) PL25-Rif<sup>R</sup>, (B) C5-Str<sup>R</sup>, (C) ScottA-Str<sup>R</sup>/Rif<sup>R</sup> and (D) 6179-Rif<sup>R</sup> grown alone (single) or in the presence of a second <i>L</i>. <i>monocytogenes</i> strain (1 day, 10°C, TSB-Y) was determined using Caco2 cells. Cells were infected for 1h with bacteria (multiplicity of infection of 25), and incubated for 45min (invasion) with gentamycin. Data, represented as % of invasion, are mean values ± standard deviation of three biological replicates performed in triplicate. *indicates significant difference of the mixed culture compared to the corresponding single culture (P<0.05). p-values are shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0141617#pone.0141617.s004" target="_blank">S3 Table</a>.</p

    <i>L</i>. <i>monocytogenes</i> strains used in this study.

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    <p><sup>a</sup> Serovar-specific groups were determined by multiplex PCR. Serotypes in parenthesis were excluded due to MLST classification.</p><p><i>L</i>. <i>monocytogenes</i> strains used in this study.</p

    Growth competition of <i>L</i>. <i>monocytogenes</i> strains.

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    <p><i>L</i>. <i>monocytogenes</i> strains (A) PL25-Rif<sup>R</sup>, (B) C5-Str<sup>R</sup>, (C) ScottA-Str<sup>R</sup>/Rif<sup>R</sup> and (D) 6179-Rif<sup>R</sup> were grown alone (single) and in the presence of a second <i>L</i>. <i>monocytogenes</i> strain in TSB-Y for 10 days at 10°C. Cultures were sampled on day 0, 1, 3, 5, 7 and 10; and CFUs were determined by plating serial dilutions on TSA-Y and TSA-Y supplemented with rifampicin or streptomycin. Data represented as log (CFU/ml) are mean values ± standard deviation of three biological replicates performed in duplicate. *indicate statistically significant differences between the co-culture and the corresponding single culture (P<0.05).</p

    <i>In vitro</i> virulence potential of <i>L</i>. <i>monocytogenes</i> strains.

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    <p>(A)Invasion efficiency and (B) intracellular growth (IGC) of <i>L</i>. <i>monocytogenes</i> strains PL25-Rif<sup>R</sup>, C5-Str<sup>R</sup>, ScottA(Str<sup>R</sup>/Rif<sup>R</sup>) and 6179-Rif<sup>R</sup> were determined using Caco2 cells. Bacteria were incubated for 1 day at 10°C in TSB-Y. Caco2 cells were infected for 1h with bacteria (multiplicity of infection of 25), incubated for 45 min (invasion) and 4h (intracellular growth) with gentamycin. IGC was calculated as the number of intracellular bacteria after 4h minus the number of bacteria after 45 min divided by the number of bacteria after 45min. Data, represented as % of invasion and IGC, are mean values ± standard deviation of three biological replicates performed in triplicate. Different letters indicate statistically significant differences between the strains (P<0.05). p-values are shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0141617#pone.0141617.s003" target="_blank">S2 Table</a>.</p

    Effect of strain competition on the intracellular growth of <i>L</i>. <i>monocytogenes</i> strains in Caco2 cells.

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    <p>Intracellular growth (calculated as IGC) of <i>L</i>. <i>monocytogenes</i> strains (A) PL25-Rif<sup>R</sup>, (B) C5-Str<sup>R</sup>, (C) ScottA-Str<sup>R</sup>/Rif<sup>R</sup> and (D) 6179-Rif<sup>R</sup> grown alone (single) or in the presence of a second <i>L</i>. <i>monocytogenes</i> strain (1 day, 10°C, TSB-Y) was determined using Caco2 cells. Caco2 cells were infected for 1h with bacteria (multiplicity of infection of 25), and incubated for 4h (intracellular growth) with gentamycin. IGC was calculated as the number of intracellular bacteria after 4h minus the number of bacteria after 45min divided by the number of bacteria after 45min. Data, represented as IGC, are mean values ± standard deviation of three biological replicates performed in triplicate. *indicates significant difference of the mixed culture compared to the corresponding single culture (P<0.05). P-values are shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0141617#pone.0141617.s004" target="_blank">S3 Table</a>.</p
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