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Experimental range and levels of the independent variables used in the 24 full factorial design for the nitrogen source study.
| Variable (g l−1) | Level | ||
|---|---|---|---|
| −1 | 0 | 1 | |
| Peptone (x1) | 0 | 6.4 | 12.8 |
| Yeast extract (x2) | 5 | 10 | 15 |
| Ammonium sulfate (x3) | 0 | 5 | 10 |
| Urea (x4) | 0 | 0.1 | 0.2 |
