TABLE 1.
Determination of protease activity in culture supernatants and reduction of measurable activity by tryptone and EDTA
| Medium | Additive | Protease activity (mU/OD600 unit) (mean ± SD) | % Reduction in measurable activity |
|---|---|---|---|
| Complete | None | 15.4 ± 0.6 | |
| Complete | Tryptone | 8.3 ± 0.4 | 46 |
| Complete | EDTA | 0.5 ± 0.1 | 96 |
| 1/4 tryptone | None | 56.9 ± 2.4 | |
| 1/4 tryptone | Tryptone | 24.8 ± 1.0 | 56 |
| 1/4 tryptone | EDTA | 0.8 ± 0.1 | 99 |
a
Aliquots of each culture were sterile filtered and immediately used for protease assays. Activity was measured by the resorufin-labeled casein assay at 574 nm after a 16-h incubation at 37°C. One unit of activity was defined as one A574 unit. The tryptone added was prepared as a 10-fold-concentrated stock (330 g/liter) in MQ water and filtered through a 0.2-μm-pore-size filter to remove insoluble debris. The amount of tryptone added was equivalent to the amount in complete medium (33 g/liter). The final concentration of EDTA (pH 8.0) was 24 mM.