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(Guillard & Lorenzen 1972, Karin Rengefors pers. com.)

We use the recipe in Guillard et al. (1972), but often use a slight modification according to Rengefors (pers. com.): TES- is used instead of TRIS buffer and selenium is added.

1. Stock solutions

CaCl2•2H2O 3.68 g/100 mL
MgSO4•7H2O 3.70 g/100 mL
NaHCO3 1.26 g/100 mL
K2HPO4•3H2O 1.14 g/100 mL
NaNO3 8.50 g/100 mL
Na2O3Si•9H2O 2.84 g/100 mL

2. Trace element solution

Na2EDTA•2H2O 4.36 g
FeCl3•6H2O 3.15 g
MnCl2•4H2O 0.18 g
H3BO3 1.00 g
1% CuSO4•5H2O 1 mL
2.2% ZnSO4•7H2O 1 mL
1% CoCl2•6H2O 1 mL
0.6% Na2MoO4•2H2O 1 mL
dH2O to 1000 mL

The pH adjusted to 4-4.5 to retain the solubility of the metals

3. f/2 vitamin solution - vitamin primary stock solutions

Biotin 0.01g/100 mL
Cyanocobalamin (B12) 0.1g/100 mL

Note: Vitamin B12 and Biotin are obtained in a crystalline form. When preparing the Vitamin B12 Stock Solution allow for approximately 11% water of crystallization (For each 1.0 mg of Vitamin B12 add 0.89 ml dH2O). When preparing the Biotin Stock Solution allow for approximately 4% water of crystallization (For each 1.0 mg of Biotin add 9.6 ml dH2O).
Keep the vitamin solutions frozen. Bottles of polyethylene are recommended for storage of vitamins.

4. f/2 vitamin working stock solution
1) Dissolve 20 mg Thiamine HCl (Vitamin B1) in ca. 80 mL dH2O in a 100 mL volumetric flask.
2) Add 1 mL of the biotin primary stock solution.
3) Add 0.1 mL of the cyanocobalamin primary stock solution.
4) Fill with dH2O to 100 mL.
The vitamin working stock solution is divided into to 10-mL lots in polyethylene vials and kept frozen until use.

Preparation of MWC-medium
Add either 115 mg TES-buffer or 50 mL 0.1% Tris-buffer and 1 mL of the stock solutions 1-6, 1 mL trace metals and 0.5 mL f/2 vitamin mix. Adjust pH to c. 7.5.

As MWC but add also 1 mL 0.002 g/L Na2SeO3•5H2O.

Guillard, R.R.L. & Lorenzen, C.J. 1972: Yellow-green algae with chlorophyllide C. J. Phycol. 8:10-14.