Table 3.
Physiological parameters of chemostat cultures (D = 0.1 h–1, 30°C) of O. parapolymorpha, K. marxianus, and S. cerevisiae, grown on glucose under aerobic (21 × 104 ppm O2 in inlet gas, 7.5 g l–1 glucose in feed medium) or oxygen-limited (840 ppm O2 in inlet gas; 20 g l–1 glucose in feed medium) conditions. Data for K. marxianus and S. cerevisiae were obtained from a previous study (Dekker et al. 2021). Growth media were supplemented with ergosterol and Tween 80, except for media for aerobic cultures of O. parapolymorpha, from which Tween 80 was omitted to prevent excessive foaming. Data are represented as mean ± standard deviation of data obtained from replicate chemostat cultures. Negative and positive biomass-specific conversion rates (q) represent consumption and production rates, respectively, with subscript x denoting biomass dry weight. B.D.: below detection limit (concentration < 0.1 mM) and (-): not applicable due to co-consumption of ethanol added as ergosterol solvent.
| O. parapolymorpha CBS11895 | K. marxianus CBS6556 | S. cerevisiae CEN.PK113-7D | ||||
|---|---|---|---|---|---|---|
| Yeast strain | Aerobic | O2-limited | Aerobic | O2-limited | Aerobic | O2-limited |
| O2 in inlet gas (ppm) | 21 × 104 | 840 | 21 × 104 | 840 | 21 × 104 | 840 |
| Replicates | 2 | 2 | 2 | 5 | 3 | 3 |
| Biomass (gx l–1) | 4.33 ± 0.06 | 0.62 ± 0.01 | 3.79 ± 0.03 | 1.57 ± 0.22 | 4.22 ± 0.11 | 2.29 ± 0.07 |
| Residual glucose (g l–1) | B.D. | 15.92 ± 0.01 | B.D. | 0.10 ± 0.03 | B.D. | 0.07 ± 0.01 |
| Biomass-specific conversion rates | ||||||
| Specific growth rate (h–1) | 0.10 ± 0.00 | 0.10 ± 0.01 | 0.10 ± 0.00 | 0.11 ± 0.01 | 0.10 ± 0.00 | 0.10 ± 0.00 |
| qglucose (mmol gx–1 h–1) | –0.94 ± 0.04 | –3.67 ± 0.20 | –1.05 ± 0.00 | –7.46 ± 0.66 | –0.95 ± 0.05 | –4.59 ± 0.18 |
| qethanol (mmol gx–1 h–1) | –0.48 ± 0.08 | 4.75 ± 0.33 | –0.52 ± 0.00 | 11.49 ± 0.97 | –0.44 ± 0.05 | 7.48 ± 0.17 |
| qglycerol (mmol gx–1 h–1) | B.D. | 0.02 ± 0.01 | B.D. | 1.12 ± 0.12 | B.D. | 0.45 ± 0.01 |
| qsuccinate (mmol gx–1 h–1) | B.D. | 0.00 ± 0.00 | B.D. | 0.02 ± 0.01 | B.D. | 0.00 ± 0.00 |
| qO2 (mmol gx h–1) | –2.35 ± 0.15 | –0.60 ± 001 | –3.52 ± 0.07 | –0.23 ± 0.05 | –2.61 ± 0.20 | –0.15 ± 0.01 |
| qCO2 (mmol gx h–1) | 2.89 ± 0.21 | 6.42 ± 0.30 | 3.73 ± 0.04 | 10.5 ± 1.1 | 2.82 ± 0.17 | 7.91 ± 0.91 |
| Stoichiometries | ||||||
| RQ (-qCO2/qO2) | 1.23 ± 0.15 | 10.7 ± 0.3 | 1.06 ± 0.01 | 49.3 ± 16.8 | 1.08 ± 0.04 | 52.2 ± 4.2 |
| Yglycerol/X (mmol gx–1) | B.D. | 0.24 ± 0.07 | B.D. | 10.7 ± 1.5 | B.D. | 4.66 ± 0.13 |
| YX/glucose (gx g–1) | 0.59 ± 0.01 | 0.15 ± 0.02 | 0.53 ± 0.00 | 0.08 ± 0.01 | 0.57 ± 0.01 | 0.12 ± 0.00 |
| Yethanol/glucose (g g–1) | - | 0.33 ± 0.04 | - | 0.39 ± 0.00 | - | 0.42 ± 0.03 |
| YX/O2 (gx mmol–1) | 0.04 ± 0.00 | 0.17 ± 0.01 | 0.03 ± 0.01 | 0.50 ± 0.18 | 0.04 ± 0.00 | 0.64 ± 0.06 |
| Recoveries (out/in) | ||||||
| Carbon (%) | 100.3 ± 0.6 | 94.4 ± 6.2 | 100.5 ± 0.1 | 91.1 ± 4.5 | 99.9 ± 1.1 | 101.2 ± 5.7 |
| Degree of reduction (%) | 97.8 ± 0.8 | 92.0 ± 6.1 | 98.8 ± 0.2 | 94.5 ± 1.0 | 98.4 ± 1.2 | 100.1 ± 1.4 |