Question

E. coli culture is given. Turbidity assay 1 OD 600 (optical
density measured at 600 nm) of this culture correlates with 1 x 10^8 cells per mL.

Q-1. how would I make 1 mL of a diluted culture of this stock
that would give a 0.25 OD 600 . (fill in the blanks below)
I would add __________ (µL) of the original culture to __________ (µL) of
media to obtain a _____ times diluted 1 mL media that would give 0.25 OD 600 .

Q-2. How many cells would I have in your diluted 1 ml culture?

Plz show work, thanks!

Answer 1

Q1. I would add 250ul of the original culture to 750ul of media to obtain 4 times diluted 1 ml of media that would give 0.25 OD 600.

Q2. Beer Lambert's law,

Where, A= absorbance, epsilon is molar absorption coefficient, C is concentration and l is pathlength.

Constants present in the equation that is epsilon and pathlength get cancel as both are the same for two OD measurements.

Now, what we have in two measurements are

1= 1×10^8, initial culture

0.25=? , Diluted culture

So dividing these two gives us

25×10^6 bacterial cells per ml.