Preparing chemically competent cells (Inoue)

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Contents

Materials

  • Plate of cells streaked for single colonies
  • SOB media
  • Ice
  • TB buffer
  • DMSO
  • Dry Ice (or liquid nitrogen)

Glassware & equipment

  • 2 liter erlenmeyer flask
  • 220 ml conical centrifuge tubes BD 35 2075
  • Eppendorf 5410R refrigerated centrifuge with conical adapters

Preparation

  1. Pick a 10 -12 large single colonies (2-3 mm dia) from your source plate and inoculate 500 ml of SOB medium in a 2 liter flask.
  2. Grow to an OD of 0.6 with vigorous shaking (200-250 rpm) at 18 degrees
  3. Prechill the centrifuge to 4 degrees
  4. Remove from the incubator and place on ice for 10 minutes
  5. Transfer to two 220 ml centrifuge tubes and spin at 3220 x g for 10 minutes at 4 degrees
  6. Drain the medium and resuspend each pellet first in 5 ml of ice cold TB. Add an additional 75 ml of cold TB buffer and resuspend.
  7. Place on ice for 10 minutes
  8. Spin down as above.
  9. Resuspend each pellet in 20 ml of cold TB
  10. Add DMSO to a final concentration of 7%
  11. Incubate on ice for 10 minutes
  12. Dispense cells into pre-chilled tubes
  13. Freeze cells in a dry ice / ethanol bath and store at -80 degrees indefinitely

Related topics & references

Original protocol from Inoue et al. [1].

  1. Inoue H, Nojima H, and Okayama H. . pmid:2265755. PubMed HubMed [Inoue90]
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