Question

Respond to this 2 part question that has different data for each:

A) The table below summarizes the results of a replica-plating experiment where a mixture of plated E. coli strains of different genotypes were tested for their ability to growth on a variety of media. It can be used to determine the number of colonies with particular phenotypes based on genotypes of Cloroamphenicol resistance (Clo^R or Clo^S), the ability to synthesize lysine (lys⁺) and the ability to synthesize phenylalanine (phe⁺). (Note, the numbers are not the same in this table as the last table)

Plate #	Medium	Number of colonies that grew
1	Complete medium (contains all amino acids, vitamins, and a variety of carbon sources)	406
2	Minimal medium (glucose as a carbon source)	285
3	Minimal medium + chloramphenicol (an antibiotic)	54
4	Minimal medium +lysine (an amino acid)	313
5	Minimal medium +phenylalanine (an amino acid)	322
6	Minimal medium +lysine+chloramphenicol	59
7	Minimal medium +phenylalanine +chloramphenicol	63

How many colonies are double-auxotrophs (lys^- phe^-)?

B) The table below summarizes the results of a replica-plating experiment where a mixture of plated E. coli strains of different genotypes were tested for their ability to growth on a variety of media. It can be used to determine the number of colonies with particular phenotypes based on genotypes of Cloroamphenicol resistance (Clo^R or Clo^S), the ability to synthesize lysine (lys⁺) and the ability to synthesize phenylalanine (phe⁺).

Plate #	Medium	Number of colonies that grew
1	Complete medium (contains all amino acids, vitamins, and a variety of carbon sources)	332
2	Minimal medium (glucose as a carbon source)	275
3	Minimal medium + chloramphenicol (an antibiotic)	44
4	Minimal medium +lysine (an amino acid)	305
5	Minimal medium +phenylalanine (an amino acid)	294
6	Minimal medium +lysine+chloramphenicol	52
7	Minimal medium +phenylalanine +chloramphenicol	66

How many colonies are wild type (lys⁺ phe⁺Clo^S)?

Answer 1

A.

Number of double auxotrophs are 121. 285 is the number of colonies which grow on only minimal medium which lacks both phenylalanine and lysine. So the bacteria which grow on minimal medium can synthesize both phe and lys. In the complete medium, there is total no of colonies and the number is 406. So the number of bacteria which are double auxotroph (lys-phe-) are 406-285 = 121

B.

The number of wild type (lys⁺ phe⁺Clo^S) colony is 231. In minimal medium the bacteria which grow can synthesize both phe and lys. and the number is 275. In minimal medium plus antibiotic chloramphenicol, only 44 colonies appear. So it is evident that out of total 275, 44 are resistant and 231 are sensitive. These 231 bacteria can synthesize both phe and lys.

So the nuber of phe+lys+ and CloS bacteria are 275-44 =231