In vitro modification of DNA for L. plantarum

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The following is a procedure for the in vitro modification of DNA before electrotransformation into Lactobacillus plantarum developed by Alegre et al. The inability to recover successful transformants in many lactic acid bacteria including Lactobacillus plantarum is most likely the result of active host restriction mechanisms. This method was originally developed for Saccharopolyspora spinosa in an attempt to circumvent the active restriction-modification of the host bacterium.


  • Stock solution of 1.0 mM AEBSF (4-(2-Aminoethyl) benzenesulfonyl fluoride hydrochloride)
  • Overnight culture of L. plantarum, OD=1.5-2.0
  • 1 mg ml BSA
  • Wash Buffer
    • 10 mM potassium phosphate
    • 10 mM EDTA
    • 50 mM NaCl
    • 0.2 mM AEBSF
  • Prepared extract
    • 50 mM Tris
    • 50 mM NaCl
    • 10 mM EDTA
    • 0.8 mM S-adenosylmethionine
    • 1 mg ml BSA
  • Prepared Plasmid DNA
  • Filtered glycerol


Preparation of the Extract

  1. Prepare a stock solution of AEBSF in water at 0.2 mM and store in a 4°C fridge.
  2. Grow up 45 ml of L. plantarum cells in MRS overnight and wait until OD600 is between 1.5 and 2.0.
  3. Pellet cells at maximum speed until supernatant is clear (∼4 mins @ 5000g).
  4. Resuspend pellet in 10 ml of wash buffer and centrifuge again.
  5. Resuspend in 2 ml of wash buffer and put cells on ice.

Keep cells chilled (on ice) during the remainder of the procedure

  1. Sonicate cells at 12 pulses of 30s with 60s intervals, using a micro tip at 60 W.
  2. Pellet cells after sonication at maximum speed ensuring cells are still cold.
  3. Carefully decant the cell extract isolating only the liquid remains.
  4. Separate into 300 ul aliquots and add 300 ul filtered glycerol and 60 ul BSA to each aliquot.
  5. The cell extract can then be stored at -20°C.

DNA Modification

  1. Add in a final volume of 100 ul the following: 50 ul solution of Tris, NaCl and EDTA. Then add 10 ul of S-adenosylmethionine,2 ul BSA, 25 ul of prepared extract and 10 ul of prepared plasmid DNA.
  2. The mixture is then incubated at 30°C for 16 hours.
  3. Extract the mixture with a phenol/chloroform extraction and then precipitate with ethanol.


All questions, input and feedback are welcome!

  1. AEBSF should be handled in a fume hood with lab coat, safety gloves and eye protection.
  2. AEBSF is a much safer alternative to PMSF that is soluble in water and has a very similar specificity to PMSF as a serine protease inhibitor. It also goes by the name Pefabloc SC.
  3. There is a helpful protocol for phenol extraction posted[1] and a protocol for ethanol precipitation posted[2].


  1. Alegre et al. (FEMS Microbiology Letters 241 (2004), 73-77)
  2. Matsushima et al. (Microbiology 140 (1994), 139-143)



or instead, discuss this protocol. -->