Yeast culture preparation, growth curve comparison and growth conditions

The yeast strains used in this study are the two laboratory strains BY4741 (Mat a his3Δ1 leu2Δ0 met15Δ0 ura3Δ0) and BY4742 (Mat α his3Δ1 leu2Δ0 met15Δ0 ura3Δ0) and four meiotic segregants of a S. cerevisiae strain isolated from Montalcino grapes fermentation (Cavalieri et al. 2000). The genetic variation between the former strains is known to be miniscule (Song et al. 2015). The latter strains share 99.99% genes. The genetic difference between M28 and the two laboratory strains is much larger.

Before the measurement of yeast VOC, the growth curves of the tested strains were compared to acknowledge eventual fitness changes. For this comparison overnight pre-grown strains were inoculated in liquid YPD (1% yeast extract, 2% peptone, 2% dextrose) in 96-well plates and their growth was monitored by measuring the optical density at 600 nm (OD600) for 24 h, a time interval sufficient to highlight the differences in growth ability of the strains (prior reaching the stationary phase). After an overnight pre-culture at 28 °C in liquid YPD the strains were inoculated onto 2 mL solid YPD medium (YPD supplemented with 2% agar) inside a 20 mL vial and closed with a screw cap with a silicon/PTFE septum. A different trend of growth curves was observable among the laboratory strains (BY4741 and BY4742) and the four M28 meiotic derivatives, with the laboratory strains showing a shorter lag phase compared to M28 strains (Table 1). This behaviour is not surprising, since the initial lag is necessary to the yeast to adapt to the environment (the fresh medium) and BY strains have been generated to show good performances in laboratory conditions (Table 1).

Growth characteristics of the tested strains

Growth curves were inspected in liquid YPD after an overnight pre-culture in the same conditions. Culture growth was evaluated by mean of optical density (OD) measurement at 600 nm