L. plantarum WCFS1 growth and metabolism in the presence of 8% (vol/vol) ethanol.
Cell growth and fermentation profiles of L. plantarum WCFS1 in MRS containing either 8% (vol/vol) additional water or 8% (vol/vol) ethanol were monitored over 24 h at 20°C (see Fig. S2 and S3 in the supplemental material). The growth temperature and alcohol concentration were selected because these conditions mimic wine fermentations and L. plantarum WCFS1 was able to reach a final OD600 close to the control condition within a few days of growth. L. plantarum WCFS1 was able to grow in the presence of 8% (vol/vol) ethanol, albeit with an approximately 5-fold-lower growth rate (0.06 ± 0.003 h−1) compared with MRS cultures (0.32 ± 0.03 h−1). The final optical density also was approximately 1.4-fold reduced in MRS containing ethanol, and this amount coincided with a more-than-2.3-fold-lower cell yield (see Fig. S2). Culture medium pH values when L. plantarum reached an OD600 of 1.0 were slightly lower for the MRS cultures (pH 5.09 ± 0.02) than for cultures in ethanol-containing MRS (pH 5.15 ± 0.02). This result might have been due to the 10-fold-larger amounts of citrate consumed per 100 μmol lactate produced during L. plantarum growth in the presence of ethanol (0.59 μmol citrate consumed) compared with control cultures (0.06 μmol citrate consumed). Conversely, lactate was the primary fermentation end product of the actively dividing cultures, but also small amounts of formate and acetate were detected (see Fig. S3).