AUTHOR=Rollero Stephanie , Bloem Audrey , Ortiz-Julien Anne , Camarasa Carole , Divol Benoit 

TITLE=Altered Fermentation Performances, Growth, and Metabolic Footprints Reveal Competition for Nutrients between Yeast Species Inoculated in Synthetic Grape Juice-Like Medium

JOURNAL=Frontiers in Microbiology

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2018.00196

DOI=10.3389/fmicb.2018.00196

ISSN=1664-302X

ABSTRACT=<p>The sequential inoculation of non-<italic>Saccharomyces</italic> yeasts and <italic>Saccharomyces cerevisiae</italic> in grape juice is becoming an increasingly popular practice to diversify wine styles and/or to obtain more complex wines with a peculiar microbial footprint. One of the main interactions is competition for nutrients, especially nitrogen sources, that directly impacts not only fermentation performance but also the production of aroma compounds. In order to better understand the interactions taking place between non-Saccharomyces yeasts and S. cerevisiae during alcoholic fermentation, sequential inoculations of three yeast species (<italic>Pichia burtonii, Kluyveromyces marxianus, Zygoascus meyerae</italic>) with <italic>S. cerevisiae</italic> were performed individually in a synthetic medium. Different species-dependent interactions were evidenced. Indeed, the three sequential inoculations resulted in three different behaviors in terms of growth. <italic>P. burtonii</italic> and <italic>Z. meyerae</italic> declined after the inoculation of <italic>S. cerevisiae</italic> which promptly outcompeted the other two species. However, while the presence of <italic>P. burtonii</italic> did not impact the fermentation kinetics of <italic>S. cerevisiae</italic>, that of <italic>Z. meyerae</italic> rendered the overall kinetics very slow and with no clear exponential phase. <italic>K. marxianus</italic> and <italic>S. cerevisiae</italic> both declined and became undetectable before fermentation completion. The results also demonstrated that yeasts differed in their preference for nitrogen sources. Unlike <italic>Z. meyerae</italic> and <italic>P. burtonii, K. marxianus</italic> appeared to be a competitor for <italic>S. cerevisiae</italic> (as evidenced by the uptake of ammonium and amino acids), thereby explaining the resulting stuck fermentation. Nevertheless, the results suggested that competition for other nutrients (probably vitamins) occurred during the sequential inoculation of <italic>Z. meyerae</italic> with <italic>S. cerevisiae</italic>. The metabolic footprint of the non-<italic>Saccharomyces</italic> yeasts determined after 48 h of fermentation remained until the end of fermentation and combined with that of <italic>S. cerevisiae</italic>. For instance, fermentations performed with <italic>K. marxianus</italic> were characterized by the formation of phenylethanol and phenylethyl acetate, while those performed with <italic>P. burtonii</italic> or <italic>Z. meyerae</italic> displayed higher production of isoamyl alcohol and ethyl esters. When considering sequential inoculation of yeasts, the nutritional requirements of the yeasts used should be carefully considered and adjusted accordingly. Finally, our chemical data suggests that the organoleptic properties of the wine are altered in a species specific manner.</p>