If the concentration of phage in the original sample was markedly increased from the concentration that you actually received for this experiment, how could you ensure that you had between 30-300 plaques on your plate

If the original concentration of a phage was markedly increased from the concentration that you received, how could you ensure that you had between 30-300 plaques on your plate? (instead of TNTC)

You receive data back from the Qubit showing that your total RNA concentration is 2.5 ug/mL. The sample run on the Qubit was diluted 100-fold, so you must correct for this to determine the actual concentration. For the same RNA sample, the Nanodrop gives you a value of 273 ng/uL.

1. How does the concentration from the Nanodrop compare to the concentration from the Qubit? SHOW your data and units conversions in your answer. Why do you think your concentrations from the Nanodrop and Qubit might be different?

2. If you need 1 ug of total RNA for the mRNA isolation step, what volume of your total RNA sample would you need (in uL) and which concentration should you use for this calculation and why?

FOR #4 A & B I don't know if I did it correctly.....Please check & the other questions I'm having a heard time on. Thanks!

A. You have been given a tube of E. coli. You are asked to make 1 mL total volume of 10^-1 dilution of the bacterial culture. Explain how you would do this. Show all necessary calculations.

____ ml cells + _____ ml water = 1 ml (total volume)

V1 D1 X V2 D2
1 mL X 1 = V2 X 10^-1
V2 = 1 mL/10^-1 so V2 = 10 mL.
But because V1 is part of V2. The answer is: 10 mL-1 mL= 9 mL of diluent must be added.

V1 D1 X V2 D2
1 mL X 1 = V2 X 10^-2
V2 = 1 mL/10^-2 so V2 = 100 mL.
But because V1 is part of V2. The answer is: 100 mL-1 mL= 99 mL of diluent must be added.

You have bacteria at a concentration of 5 x 10⁸ CFU/mL. You spread 1 mL of this sample on an agar plate to obtain isolated colonies. How many colonies do you expect to find the next day after incubation at 37⁰C? Can you count these colonies? Can you use this plate for determining concentration?

A. You have bacteria at a concentration of 1 x 10³ CFU/mL (in real life – you don’t know this, but we are just working on math skills here). You transfer 1 mL of this sample into 9 mL of water and then spread 1 mL on a plate of agar. How many colonies do you expect to find the next day after incubation at 37⁰C? Can you count these colonies? Can you use this plate for determining concentration?

You take 0.05 mL of a culture of bacteria at a concentration of 4 x 10⁷ CFU/mL, and add 4.95 mL of water to it. What is the dilution that you have performed? What is the concentration of bacteria (CFU/mL) in the diluted culture?

A. You have diluted a sample by 1000 fold (1/1000) and plated 1 mL on an agar plate. You observe 55 colonies. What was the concentration of the original sample in CFU/mL?

A. A bacterial sample has a concentration of 3 x10⁷CFU/mL. You make serial dilutions of 10^-3 followed by 10^-2 and 10^-1 dilutions. You finally plate 1 mL of the last dilution on an agar plate and incubate it at 37⁰C. What is the total dilution? How many colonies do you expect to see on the plate?

Total dilution:

# of colonies expected on plate:

C. This time, you see 10 times fewer colonies than you had expected to see.What could have gone wrong? How will you fix this problem?

A bacterial sample has a concentration of 2 x10⁶ CFU/mL. Show a scheme of dilutions to obtain 30-300 colonies on a plate. Your scheme should contain the volume of diluent (sterile water), volume of sample transferred each time, the concentration of bacteria (CFU/mL) in each dilution. You can assume you are plating 1 mL of the dilution on plates of nutrient agar. See Figure 1 in protocol.

These are the results of the experiment described in the protocol. From the data shown in the results section of Standard Plate Count protocol, calculate the concentration of bacteria (CFU/mL) in the original sample of E. coli. Show your calculations. Hint: remember that we don’t use plates that have less than 30 or more than 300 colonies to do these calculations.