Team:NTNU-Trondheim/Protocols

Laboratory Protocols

Transformation

Official iGEM [http://parts.igem.org/Help:Protocols/Transformation Transformation protocol].

We used this protocol with these modifications:

• Heat-shock 45 seconds instead of 60 seconds
• Incubation for min 1 hour with shaking at 37°C, not 2 hours.
• LB medium instead of SOC.

Transformed cells

Use a sterile toothpick, scratch a single colony from the transformed cells. Place the toothpick into a plastic tube with 4 mL sterile liquid medium with the appropriate antibiotic(s). Cap the tube and incuate at 37°C with shaking.

DNA Isolation

We use the Promega Wizard Plus SV Minipreps DNA Purification System A1460 [http://www.promega.co.uk/~/media/Files/Resources/Protocols/Technical%20Bulletins/0/Wizard%20Plus%20SV%20Minipreps%20DNA%20Purification%20System%20Protocol.pdf Miniprep protocol].

Small-Scale Vesicle Preparation

1. Start a culture by adding 2μL of cell-culture or one colony in 5 mL of LB. Incubate the cell culture for 7-8 hours at 37°C.

2. Inoculate 1 mL of the overnight starter culture in each of (up to six) 500 mL-flasks containing 250 mL of LB.

3. Grow cultures at the desired temperature for the desired time and agitation. About 12-14 hours at 37°C for E.coli.

4. Determine cell-number (CFU) by finding the optical density (OD) at 600 nm. NB! If the OD₆₀₀ is over 1, dilute the solution with LB-medium so it is under 1 (note how much you diluted).

5. To obtain vesicle-containing, cell-free supernatant for non-encapsulated strains, pour 240 mL of the growth culture into 250 mL bottles using a graduated cylinder and centrifuge at 9,715 × g (using the SLA-1500 rotor at 8000 rpm) for 10 min.

6. Collect the supernatant in a sterile container, and filter it through a 0.45 μm Durapore PVDF Millipore vakuum filter. Filter the supernantants into new sterile 250 mL centrifugation bottles.

7. Centrifuge the filtered supernatant at 31 916 × g for 2.5 h (using the SLA-1500 rotor at 14 500 rpm) NB! The vesicle pallet may not be visible, mark on the tube were the pallet will form.

8. Be ready for when the centrifugation start to deacclererate and dont let it sit in the rotor for long. NB! Keep your eyes on the pallet! If it disappears, stop decanting and redo step 8. Collect the supernantant in a sterile container in the case of that recentrifugation is necessary.

9. Resuspend the vesicle-containing pellet in the residual supernatant remaining in the centrifuge bottle after decanting (approximately 5.5 mL so that the 10.4 mL tubes are at least half full) or re-suspend in 5.5 mL fresh DPBSS. Transfer to ultracentrifuge tube and centrifuge in ultracentrifuge at 100,000 × g for 1 h (using the type 70.1 ti rotor at 38 247 rpm). NB! Make sure that the centrifuge de-acceleration function stands on “No break” (Not “fast” or “slow”) and be ready for decanting the vesicle pallet when the centrifuge is finished (as in step 8).

10. Decant the supernatant and resuspend the pellet in 500 μL DPBSS (add more if the pallet is too big and note down how much more DPBSS you added). The resuspended pellet is the vesicle preparation. To freeze the sample at -80°C add OptiPrep 60% so that the final sample contains 45% OptiPrep.

11. Filter-sterilize the vesicles using a 0.45 μm centrifugal filter or a syringe filter. Check for sterility by plating on LB agar (optional). Re-sterilize using 0.45 μm filters if needed.

12. To quantitate the vesicle yield in terms of mg vesicle protein/CFU, use a protein concentration determination assay to determine the total protein concentration in the vesicle preparation and divide the number by the CFU obtained from dilution plating of the culture at the time of harvest. In some cases, flagella and other non-vesicle proteins contaminate the preparation; however, further purification steps (e.g., using density gradient purification) prevent quantitative recovery. Therefore, vesicle yields often can be best compared using the quantity of vesicle-specific protein or lipid in the pelleted cell-free supernatant preparations. Here, an aliquot of the vesicle preparation is run on SDS-PAGE, stained for protein using Ruby or Coomassie, and either the total protein in each sample or the major outer membrane proteins (e.g., Omps F/C and A for E. coli ) in each sample are determined by densitometry. Subsequently, the densitometry value is divided by the CFU and this vesicle yield compared between strains or treatments. Finally, vesicle yield can also be determined based on lipid content using FM4-64, a lipophilic fluorescent dye. For FM4-64-based measurements, 20 μL vesicle preparation is diluted in 560 μ L of DPBSS, and 20 μL FM4-64 (1mg/mL) is added. Fluorescence (RFU) is measured with an excitation of 506 nm and emission of 750 nm using a spectro fluorometer. Subsequently, the RFU value is divided by the CFU and this vesicle yield value compared between strains or treatments.

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