SOB

Summary

SOB Medium. Used in growing bacteria for preparing chemically competent cells

Ingredients

• 0.5% (w/v) yeast extract
• 2% (w/v) tryptone
• 10 mM NaCl
• 2.5 mM KCl
• 20 mM MgSO₄

Per liter:

• 5 g yeast extract
• 20 g tryptone
• 0.584 g NaCl
• 0.186 g KCl
• 2.4 g MgSO₄

Note: Some formulations of SOB use 10 mM MgCl₂ and 10 mM MgSO₄ instead of 20 mM MgSO₄.

SOB medium is also available dry premixed from Difco, 0443-17.

Adjust to pH 7.5 prior to use. This requires approximately 25 ml of 1M NaOH per liter.

15/10 medium

Growth of competent TOP10 cells in Example 2 of the Bloom05 patent is performed in 15/10 broth, which is similar to SOB:

• 1.5% yeast extract
• 1% Bacto-Tryptone
• 10mM NaCl
• 2mM KCl
• 10 mM MgCl₂
• 10 mM MgSO₄

Extended instructions

• 1 M MgCl2 stock: dissolve 20.33 g MgCl2 6H2O in 100 ml ddH2O (XXX), autoclave on liquid cycle @ XXX°C for 20 min (can be done at the same time as SOC pre-mix below)
• 250 mM KCl stock: dissolve 1.86 KCl in 100 ml ddH2O (XXX)

• combine:

Reagent	for 1 L	500 mL	100 mL
tryptone	20 g	10 g	2g
yeast	5g	2.5 g	0.5 g
NaCl	0.5 g	0.25 g	0.05 g
250 nM KCl	10 mL	5mL	1 mL
ddH2O	980 ml	490 ml	98 ml

• adjust pH to 7.0 w/ NaOH
• bring to volume:

Reagent	for 1 L	500 mL	100 mL

• autoclave on liquid cycle @ XXX°C for 20 min

• add autoclaved 1 M MgCl2

Reagent	for 1 L	500 mL	100 mL
1 M MgCl2	10 ml	5 ml	1 ml

Source

Adapted From:

F. Ausubel et al., Short Protocols in Molecular Biology (John Wiley & Sons, ed. 4, 1999) pg. A1-36

Trivia

SOB supposedly stands for super optimal broth.