Minimal growth medium for bacteria such as E. coli includes various salts with c
ID: 56339 • Letter: M
Question
Minimal growth medium for bacteria such as E. coli includes various salts with characteristic concentrations in the mM range and a carbon source. The carbon source is typically glucose and it is used at 0.5% (a concentration of 0.5 g/100mL). For nitrogen, minimal medium contains ammonium chloride (NH4Cl) with a concentration of 0.1 g/100mL.
(a) Make an estimate of the number of carbon atoms it takes to make up the macromolecular contents of a bacterium such as E. coli. Similarly, make an estimate of the number of nitrogens it takes to make up the macromolecular contents of a bacterium? What about phosphate?
(b) How many cells can be grown in a 5mL culture using minimal medium before the medium exhausts the carbon? How many cells can be grown in a 5mL culture using minimal medium before the medium exhausts the nitrogen? Note that this estimate will be awed because it neglects the energy cost of synthesizing the macromolecules of the cell.
[HINT] 1. Glucose C6H12O6 , 180Da 2. Roughly 5 carbons/amino acid , 20 carbons/base pair , 40 carbons/lipid
Explanation / Answer
Based on the given data,
a)
The dry weight of E.coli = 0.3 pg
Since, chemical composition of E.coli is ~ 50% of carbon and 14 % of nitrogen. Therefore, number of carbon atoms per cell required to make up the macromolecular contents:
So, to get number of carbon atoms,
Next, the number of nitrogen atoms required per cell:
So, to get number of nitrogen atoms,
Phosphate atoms are mainly present in the form of ATPs. So, an E.coli cell growing on glucose as the carbon source requires ~ 10-20×109 ATPs.
b)
Number of glucose molecules present in media initially:
So, molecules of glucose can support the growth of
Where, 0.5% is the concentration glucose, 5 ml of culture media and number of required =Ne/6 = 1.25 ×109
The number of amount of (nitrogen molecule):