SOB

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Contents

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.

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