Cell harvest

• The following harvest protocol mainly orientates to the procedures in Sun et al. 2013 and Kwon and Jewett 2015.
• Gather all materials needed: Harvest tubes and falcon tubes, washing buffer, DTT aliquot, liquid nitrogen, and a lot of ice. Start the harvest when E. coli culture reaches mid- to late exponential growth phase. For the E. coli we used in our experiments and cultivations, the mid- to late exponential growth phase was reached at an OD₆₀₀ of 3-4 (see growth curves in protocol section).
• harvest protocol - keep everthing on ice between the steps!
1. Transfer culture into prechilled and weighted harvest tubes or falcons
2. Centrifugate: 5000x g, 4 °C, 15 min. While centrifugating, add DTT to S30 buffer to a final concentration of 2 mM
3. Discard supernatant and weight pellets
4. Add about 10 mL of S30 washing buffer and resuspend cells by vortexing and vigourous shaking. For us, cycles of 15 s vortexing/shaking and 30 s resting on ice worked well.
5. Centrifugate: 5000x g, 4 °C, 12 min
6. Discard supernatant
7. Repeat steps 4 to 6 two times
8. Centrifuge a last time at 5000x g, 4 °C, for 5 min and remove residual washing buffer by pipetting.
9. Flash freeze pellets in liquid nitrogen and store at -80 °C, unless you want to proceed with sonification directly.

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• Thaw 50 µl electrocompetent E. coli cells on ice, dilute with icecold 50 µl glycerine (10%) if necessary
• Add 0.5-5 µl plasmid to 50 µl electrocompetent cells
• Store cells on ice for 1 minute
• Electroporate at U = 2.5 kV, C = 25 µF, R = 400 Ω
• Transfer transformation reaction to 450 µl SOC-Medium and incubate 1 h at 37 °C
• Plate on selective LB-Medium
• Incubate over night at 37 °C

• Thaw 100 µl chemo competent E. coli cells on ice
• Add 0.5-5 µl plasmid to 100 µl chemocompetent cells
• Store cells on ice for 10-30 min on ice
• Heat shock for 90 seconds at 42 °C
• Store reaction on ice for 60 seconds
• Optional: Preheat SOC medium to 37 °C
• Transfer reaction to 1 ml SOC medium and incubate at 37 °C for at least 1 hour
• Centrifuge 3 minutes at 12000 rpm and plate on selective LB medium
• Incubate at 37 °C over night

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