1. You have an experiment that requires you to have 108
CFU of E. coli in 1 ml of broth - and no more. At 5:00 p.m. you
inoculate your 1 ml of L broth with 500 CFU of E. coli. The doubling
time for the strain is 20 min. What time will you have to come into lab
to harvest your culture and perform your experiment?
2.
You inoculate another culture of E. coli at 3000 CFU/ml.
Five hours later, you have 48,000 CFU/ml.
A. What was the doubling/generation time?
B. What was the growth rate?
3. You have cloned your favorite protein into E. coli, but
unfortunately you are abusing the lowly bacteria and making them produce
something that they don’t like. Expression of your protein causes the growth
rate to decrease by 50%. The normal growth rate for E. coli in L broth
is 3 g/h. You want to grow up a culture of your strain to harvest the protein,
so you inoculate a broth with 1,000 cells; however, there is 1 additional cell
that is a mutant that no longer expresses your protein and has a normal
growth rate of 3 g/h. If the culture grows for 10 hours, when you harvest the
culture to get your protein what proportion of the culture
will consist of wild-type clones still expressing your protein versus mutant bacteria
that have stopped expressing your protein?
4. The mass of an E. coli
cell is 10-12 g, and the mass of the Earth is roughly 1028
g. If a mutant E. coli was capable of using everything on the
Earth as if it were L agar and grew with a doubling time of 30 minutes, how
long would it take for that single mutant E. coli cell to convert the
entire planet into a giant ball of E. coli?