OP50 solution

Prepare E. coli strain OP50 for worm feeding as follows:

• 1. Make a fresh streakout of OP50 from a glycerol stock onto an LB plate without antibiotics.

• 2. Inoculate two 1-mL precultures from individual colonies in LB medium.

• 3. Inoculate two 1-L batches of LB medium without antibiotics with the 1-mL precultures. Grow overnight at 37°C with shaking at 200 rpm.

• 4. Collect the bacteria by centrifuging in 1-L centrifuge cups for 15 min at 2000g.

• 5. Decant the supernatant and resuspend each cell pellet under sterile conditions in 35 mL of fresh LB medium to obtain a total volume of 80 mL.

• 6. Keep the OP50 solution at 4°C until use.

  Alternatively, cultivate OP50 in a fermenter. Store stocks in LB medium and 5% glycerol at −80°C. Dilute the bacteria to reach 0.16 mg OP50 per 1 mL suspension in LB medium before plating.