Competent Cells

Preparation of Bacillus subtilis competent cells

Streak out the strain to be made competent on an LB agar plate as a large patch and incubate overnight at 30°C

The following morning scrape the cell growth off the plate and use to inoculate fresh, pre-warmed, SpC medium (20 ml) to give an OD600 reading of about 0.5.

Incubate the culture at 37°C with vigorous aeration and take periodic OD readings (OD600) to assess cell growth.

When the rate of cell growth is seen to depart from exponential (i.e. no significant change in cell density over 20-30 min) inoculate 200 ml of pre-warmed, SpII medium with 2 ml of stationary-phase culture and continue incubation at 37°C with slower aeration

After 90 min incubation, pellet the cells by centrifugation (8,000 g, 5min) at room temperature.

Carefully decant the supernatant into a sterile container and save.

Gently resuspended the cell pellet in 18 ml of the saved supernatant and add 2 ml of sterile glycerol; mix gently

Aliquot the competent cell (0.5 ml) in sterile tubes, freeze rapidly in liquid nitrogen or a dry-iced/ethanol bath or ice/isopropanol bath and store -70.

Transformation

Cells Preparation :

Thaw competent cells rapidly by immersing frozen tubes in a 37°C water bath

Immediately, add one volume of SpII + EGTA to the Thawed cells; mix gently

In a sterile test tube add competent cell (0.2~0.5 ml) to the DNA solution (<0.1 ml) and incubate in a roller drum at 37.

Dilute the transformed cells as appropriate in T base containing 0.5% glucose and plate immediately onto selective media.