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A. Media for freshwater cyanobacteria
CHU-10Chu No. 10 (Chu-10 medium)
Classical oligotrophic medium
- Application
- Diatoms (Asterionella, Fragilaria), desmids, planktonic cyanobacteria; modelling of natural waters
- pH
- 6.5–7.0
- Source
- Chu, 1942; modified by Gerloff et al., 1950
Composition
| Component | Amount per 1 L |
|---|---|
| Ca(NO₃)₂ | 40 mg (or Ca(NO₃)₂·4H₂O 57.6 mg) |
| K₂HPO₄ | 10 mg |
| MgSO₄·7H₂O | 25 mg |
| Na₂CO₃ | 20 mg |
| Na₂SiO₃·9H₂O | 25 mg |
| FeCl₃ (or ferric citrate) | 0.8 mg |
| Chu-10 trace element solution | 1.0 mL |
| Distilled water | to 1000 mL |
Trace element solution for Chu-10 (Gerloff modification)
per 100 mL of solution · usage rate 1 mL per 1 L of medium · storage at 4 °C, 6 months
| Component | Weighed amount / volume |
|---|---|
| Na₂EDTA | 100 mg |
| H₃BO₃ | 50 mg |
| MnSO₄·4H₂O | 50 mg (or MnCl₂·4H₂O 44 mg) |
| ZnSO₄·7H₂O | 5.0 mg |
| CuSO₄·5H₂O | 2.0 mg (1 mL of a primary stock solution at 2.0 g/L) |
| Na₂MoO₄·2H₂O | 1.0 mg (1 mL of a primary stock solution at 1.0 g/L) |
| Co(NO₃)₂·6H₂O | 1.0 mg (1 mL of a primary stock solution at 1.0 g/L) |
| Distilled water | to 100 mL |
Preparation
Dissolve K₂HPO₄ → MgSO₄·7H₂O → Na₂CO₃ → FeCl₃ (from a freshly prepared dilution) → 1 mL of the trace element solution → Ca(NO₃)₂ → make up to 950 mL → adjust the pH to 6.5–7.0 → and only then add Na₂SiO₃·9H₂O → make up to 1000 mL.
Notes
- The silicate is added AT THE VERY END and only to a medium already brought to its working pH. Adding Na₂SiO₃ to an acidic medium precipitates amorphous SiO₂, which is unavailable to diatoms; adjusting the pH after the silicate has been added gives the same result.
- Modified Chu-10 (after Gerloff) additionally contains EDTA and a full set of trace elements; Chu's classical formulation has no trace elements and is suitable only for short-term experiments.
- For non-diatom cultures Na₂SiO₃·9H₂O is omitted.
- Na₂EDTA is dissolved first: in oligotrophic media without a chelator the trace elements co-precipitate with carbonates and become unavailable to the cells. The three primary stock solutions are prepared in 100 mL (200, 100 and 100 mg respectively) and 1 mL is taken from each.