Question

You begin working in a research lab on campus. In the lab's freezer you find a tube of preserved bacterial cells. You want to grow the cells, but you do not know what their nutritional requirements are. What type of growth medium would be best? Could someone please explain to me why this is the correct answer? I am still unsure on whether I fully understand complex and define (minimal) media as well.

Incorrect Minimal medium supplemented with only essential growth factors
Incorrect Complex medium supplemented with inorganic nitrogen
Correct: Complex medium supplemented with a variety of growth factors
Incorrect Minimal medium supplemented with minerals, a carbon, nitrogen, and energy source
Incorrect Minimal medium supplemented with a variety of growth factors

Answer 1

The answer is a complex medium with some growth factors.

Firstly, a defined medium means that we know what its constituents are and in wht concentrations.

eg: Minimal media – Stock 5X ( 200 ml )

· 6 g Na2HPO4

· 3 g KH2PO4

· 0.5 g NaCl

· 1 g NH4Cl

MgSO4 – 1 M

CaCl2 – 0.01M

10 % lactose

10 % glucose

On the other hand, we do not know what all is present in a complex medium and in what concentrations.

eg: Luria-Bertani broth medium - it contains yeast extract, tryptone, NaCl

But yeast is a complex organism and contains several different micro and macronutrients, proteins, lipids, nucleic acids, etc. We do not know what all is present and in what amounts. Thus, its a complex medium

Now coming back to the question,

If you are handling a bacterial strain about which you do not know what are its nutritional requirements, better first grow it in a complex medium likeLB broth. Since, it contains all the essential components the bacterial strain would grow on it with addition of some growth factors.

Once you have a culture of it, then you may go on to find its nutritional requirements by plating on minimal media lacking 1 or more of the nutients like maino acids, carbohydrates, vitamins, etc.