Question

MICROBIO HELP PLEASE!
Working in a lab, you’ve set up an E. coli culture for a critical experiment where you need to grow the cells at 27 degrees C until they reach a cell density of exactly 6 x 108 cells/ml and then you will need to rapidly harvest them to perform a critical bioassay. Unfortunately, you used a very old stationary culture to inoculate your culture and so the cells spent a lot of time in lag phase before they entered into exponential growth.

Answer 1

Continued: Consequently, it’s now 8:30 pm, you haven’t had dinner and you’re so hungry that you’re actually considering eating a very suspicious looking (and smelling) chicken taco that you put in your backpack this morning and then forgot to put in the refrigerator when you reached the lab (see question 1). It suddenly occurs to you that there’s a sandwich place that’s open till 9 pm and you can get there on your bike before closing time and make it back to the lab by 9:30 pm.

You really want that sandwich but if your cells reach a density of > 6 x 108 cells/ml before you get back they cannot be used for the bioassay and you’ll not only have to start all over again tomorrow but will also have to endure snarky comments from your lab supervisor who will point out that you should have planned things better.

When you measured the cell density at 8:30, it was 2 x 108 cells/ml but, unfortunately, you don’t know the generation time of this strain of E. coli at 270C (you usually grow the cells at 37 degrees C and you know that the generation time at that temperature is 30 min). But then you remember your beloved Microbiology professor yammering on about something called the Ahrennius equation and…

A) Do you have time to go get that sandwich?


B) What is your best estimate for the time the cells will be ready for harvest? Show you work.