genotype of E coli colony? please help!

[orangeblossom]

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This is from a TPR bio passage, #13 if you have the hyperlearning book

The first question is: What is the genotype of Colony I, Experiment I?
The answer is: Lac+ Arg+ Leu+ Thr-

Here is the image shown in Experiment 1:

"Experiment 1: A mixture of E Coli strains with differing nutrient requirements is plated onto solid media containing the amino acids arginine, leucine, and threonine, glucose as the carbon source and certain necessary salts. From this plate, colonies are replicated onto five additional plates (A through E below) supplemented with different combinations of nutrients. Dots indicate numbered colonies that have grown."

TPR ANSWER EXPLANATION: Since the colony can grow with only lactose as a carbon source (Plate B), it is Lac+. Since it can grow without arginine (Plate D), and leucine (Plate C), but cannot grow without threonine (Plate E), it is also Arg+Leu+Thr-

edit: nevermind, figured it out.

 

[sciencebooks]

This is from a TPR bio passage, #13 if you have the hyperlearning book

The first question is: What is the genotype of Colony I, Experiment I?
The answer is: Lac+ Arg+ Leu+ Thr-

Here is the image shown in Experiment 1:

"Experiment 1: A mixture of E Coli strains with differing nutrient requirements is plated onto solid media containing the amino acids arginine, leucine, and threonine, glucose as the carbon source and certain necessary salts. From this plate, colonies are replicated onto five additional plates (A through E below) supplemented with different combinations of nutrients. Dots indicate numbered colonies that have grown."

TPR ANSWER EXPLANATION: Since the colony can grow with only lactose as a carbon source (Plate B), it is Lac+. Since it can grow without arginine (Plate D), and leucine (Plate C), but cannot grow without threonine (Plate E), it is also Arg+Leu+Thr-

edit: nevermind, figured it out.

Just to double check with you, with sugars isn't it + if it can digest and - if it cannot and then for amino acids, + if it can synthesize and - if it cannot. Something like that?