Team:NTNU Trondheim/Demonstrate


Having characterized our own phage, we evolved a resistant bacterium against it using a single chemostat setup over the course of 24 hours. Samples of the culture were then plated out and three resistant bacterial colonies were further studied (Res1 , 2 and 3). We characterized them together with the unevolved Escherichia coli strain (control) for resistance to phage. We found that none of the resistant colonies showed signs of infection after two hours, but after five hours one of the two repeats of Res2 and both repeats of Res3 were lysed, indicating that phage that were potent against these strains were present in small quantities in our sewage phage sample. Five hours is about three generations. Thus the occurrence frequency of these phage in the original phage sample was about 10-6-10-7.

Three strains of phage-resistant E. coli challenged with phage they were evolved against (sewage phage).

We then performed a round of phage evolution using our three chemostat system on the original E. coli strain and the Res1 strain (that was not lysed by the original phage even after 8 hours). We purified phage from the phage-evolving chemostat and tested the phage on our original strain as well as on all the resistant ones. Our new phage sample lysed all strains within 1.5 hours after induction, indicating that the newly evolved phage was highly enriched in the sample. This gave us the proof of concept that we were aiming for: We first evolved bacteria that were resistant to our original phage strain and then we managed to evolve a new strain of phage that could lyse the resistant bacteria (in addition to the old ones)!

Three strains of phage-resistant E. coli challenged with phage evolved in chemostat.