The aim of the study was to investigate the uptake of nitrogen sources by Starm. bacillaris and how it compares to Saccharomyces cerevisiae. The effect on the central carbon metabolite production was also investigated.
Experimental layout
- One S. cerevisiae strain, Uvaferm BC, and two Starm. bacillaris strains were evaluated in this study.
- Fermentations were conducted in synthetic grape must: SM200.
- The medium contained equal amounts of glucose and fructose but differentiating amounts of amino acids and ammonium, generating three different musts.
- Fermentations were conducted in 330 ml glass containers.
- Various analyses were performed on the musts during fermentation as well as after fermentation.
Main results
- Uvaferm BC fermented to dryness with a clear preference for glucose (depletion after 118 hours versus 142 hours for fructose depletion).
- The two Starm. bacillaris strains fermented slower and got stuck at approximately 340 hours. Glucose remained untouched but almost all the fructose was depleted (3.7 – 11.3 g/l residual fructose).
- The Starm. bacillaris strains had higher glycerol yields and lower acetic and succinic acid yields than Uvaferm BC.
- The Starm. bacillaris strains produced higher amounts of other organic acids, which resulted in a decrease in pH and an increase in titratable acidity.
- The final volume of volatile metabolites were lower for the Starmerella fermentations than for Uvaferm BC.
- For Uvaferm BC YAN was completely depleted after 30 hours of fermentation. For the Starmerella strains only 41 – 64% of the YAN was depleted by the time the yeasts reached the stationary phase. Only ammonia was depleted after 150 hours of fermentation. After fermentation stopped 50 – 80% of the initial concentration of amino acids remained in the medium.
- Uvaferm BC took up all the amino acids in the medium except proline.
- The Starmerella strains took up all the ammonium in the medium and consumed only some amino acids up to 40% of their initial concentration. Some amino acids remained constant during fermentation meaning, they were not utilised and some increased, meaning they were produced.
- Despite results showing a clear preference for ammonia in the case of the Starmerella strains when YAN was mixed, the strains showed better growth and fermentation performance when YAN consisted only of only amino acids.
Significance of the study
Starm. bacillaris seems to have limited nitrogen requirements and in addition it secretes some amino acids that can be very beneficial for S. cerevisiae during sequential inoculation in terms of volatile aroma production. In addition to its other positive traits of being fructophilic and producing less alcohol per gram of sugar consumed, Starmerella bacillaris is a very likely candidate for commercialisation.
Reference
Vasileios Englezos, Luca Cocolin, Kalliopi Rantsiou, Anne Ortiz-Julien, Audrey Bloem, Sylvie Dequin, Carole Camarasa. Specific Phenotypic Traits of Starmerella bacillaris Related to Nitrogen Source Consumption and Central Carbon Metabolite Production during Wine Fermentation. Appl. Environ. Microbiol. Aug 2018, 84 (16) e00797-18; DOI: 10.1128/AEM.00797-18
