How do you harvest E. coli cells?

E. coli cells are typically harvested by centrifugation to form a cell pellet. This allows for the separation of the cells from the growth medium.

Harvesting E. coli Cells by Centrifugation

The most common method for harvesting E. coli cells is through centrifugation. Here's a breakdown of the process:

Centrifugation: Transfer the E. coli culture to centrifuge tubes or bottles suitable for your centrifuge rotor.
Centrifuge Settings: Centrifuge the culture at 4,500–6,000 g for approximately 15–20 minutes. This can be done at room temperature or at around 4 °C. Lower temperatures can help protect temperature-sensitive proteins.
Pelleting: The centrifugation process will force the E. coli cells to the bottom of the tube, forming a visible pellet.
Supernatant Removal: Carefully remove the supernatant (the liquid above the pellet) by decanting or aspiration, being careful not to disturb the cell pellet. The supernatant contains the spent growth medium and any secreted proteins (if applicable), and can be discarded or saved for downstream analysis, depending on the experiment.
Resuspension (Optional): The cell pellet can then be resuspended in a buffer of choice, depending on the downstream application. Common buffers include PBS (phosphate-buffered saline), Tris-HCl, or specialized lysis buffers.

Scale: The centrifugation speed and time may need to be adjusted depending on the volume of the culture and the type of centrifuge being used. Larger volumes may require higher g-forces or longer centrifugation times.
Strain: Some E. coli strains may pellet more efficiently than others. It may be necessary to optimize the centrifugation conditions for specific strains.
Application: The buffer used to resuspend the cells should be compatible with the downstream application. For example, if the cells are to be lysed for protein purification, a lysis buffer containing detergents or enzymes may be used.