The effects of cell-cell contact between Pichia kluyveri and Saccharomyces cerevisiae on amino acids and volatiles in mixed culture alcoholic fermentations.

This study used a double-compartment fermenter to assess yeast growth, fermentation activity, and aroma production in response to cell-cell contact during mixed culture fermentation of Pinot noir grape must with Pichia kluyveri and Saccharomyces cerevisiae. Furthermore, amino acids were analyzed in order to study yeast interactions and possible reasons for aroma modulation as a response to cell-cell contact. Our results show that cell-cell contact between the two yeasts decreased cell viability of each yeast during mixed culture fermentation, and that it increased acetate and ethyl ester production and decreased varietal volatile levels. Moreover, it increased the consumption of glutamic acid and the biosynthesis of some specific amino acids related to cell growth, mainly histidine, glycine and proline, while suppressing the production of higher alcohols through the Ehrlich pathway. These results may contribute to an improved understanding, and thus control, of aroma production in mixed culture wine fermentations.

Finding Functional Differences Between Species in a Microbial Community: Case Studies in Wine Fermentation and Kefir Culture.

Microbial life usually takes place in a community where individuals interact, by competition for nutrients, cross-feeding, inhibition by end-products, but also by their spatial distribution. Lactic acid bacteria are prominent members of microbial communities responsible for food fermentations. Their niche in a community depends on their own properties as well as those of the other species. Here, we apply a computational approach, which uses only genomic and metagenomic information and functional annotation of genes, to find properties that distinguish a species from others in the community, as well as to follow individual species in a community. We analyzed isolated and sequenced strains from a kefir community, and metagenomes from wine fermentations. We demonstrate how the distinguishing properties of an organism lead to experimentally testable hypotheses concerning the niche and the interactions with other species. We observe, for example, that L. kefiranofaciens, a dominant organism in kefir, stands out among the Lactobacilli because it potentially has more amino acid auxotrophies. Using metagenomic analysis of industrial wine fermentations we investigate the role of an inoculated L. plantarum in malolactic fermentation. We observed that L. plantarum thrives better on white than on red wine fermentations and has the largest number of phosphotransferase system among the bacteria observed in the wine communities. Also, L. plantarum together with Pantoea, Erwinia, Asaia, Gluconobacter, and Komagataeibacter genera had the highest number of genes involved in biosynthesis of amino acids.