Plus minus notation in microbiology?

[circulus vitios]

Can someone show me a webpage that summarizes and gives examples of the plus and minus notation commonly used to describe mutations e.g. lac+, arg-, etc. My review book is way too brief and kind of confusing. I tried searching but the results aren't what I want.

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[Leonardo Noto]

Can someone show me a webpage that summarizes and gives examples of the plus and minus notation commonly used to describe mutations e.g. lac+, arg-, etc. My review book is way too brief and kind of confusing. I tried searching but the results aren't what I want.

Way back when people still ate stegosaurus burgers, I used to work with E. coli and the Lac operon. A Lac (+) organism is one that can metabolize lactose and a Lac (-) organism is one that cannot. Organisms that metabolize lactose produce colored colonies on MacConkey agar plates whereas organisms that cannot metabolize lactose produced colorless colonies (google search an image so that you can see it for yourself). Microbiology tests usually use a flowchart to determine what kind of organism you have: e.g. the first step might be Gram (+) or Gram (-), the second step to determine whether you are working with rods or cocci, the third step whether an organism can metabolize lactose, and so forth until you finally identify your organism.

I believe that the Arg (+)/Arg (-) refers to this test, http://www.vumicro.com/vumie/help/VUMICRO/Arginine_dihydrolase_Test.htm, but hopefully someone who is closer to the textbooks will double-check me on this. ******************************I was wrong here (in this sentence)--see two posts down for the correct answer (at least in the context of this question)******************************************

Here are examples of flow charts for determining what organism you're working with:

http://alkam.tripod.com/gramn.gif
http://alkam.tripod.com/gramp.gif

The Lac operon was "the first control system for enzyme production worked out at the molecular level" and it commonly shows up on the MCAT, both because it is the classic example of how an operon works and because all of the guys who write the genetic/molecular biology questions for the MCAT know this particular operon like the back of their hand. Here is a website that explains the Lac operon, although I have seen several examples that are more user-friendly:
http://www.ndsu.edu/pubweb/~mcclean/plsc431/prokaryo/prokaryo2.htm. What review book are you using?

Dr. Leonardo Noto
www.leonardonoto.com or follow me on Twitter @DrLeonardoNoto

 

[circulus vitios]

I have another question from a TPR-H passage. 😳

Plate D of Experiment 1 contains glucose, leucine, and threonine.

Which of the following genotypes could grow on Plate D of Experiment 1?

I. Lac+, Arg+, Leu+, Thr+
II. Lac-, Arg-, Leu+, Thr+
III. Lac-, Arg+, Leu-, Thr-

I obviously grows on Plate D.
II obviously will not grow on Plate D because D lacks arginine.
III supposedly grows on Plate D.

Lactose is a dissacharide so Lac- means it cannot metabolize lactose. What does this mean within the context of the problem and how do I use it to decide that III will grow on the plate?

 

[Leonardo Noto]

I have another question from a TPR-H passage. 😳



I obviously grows on Plate D.
II obviously will not grow on Plate D because D lacks arginine.
III supposedly grows on Plate D.

Lactose is a dissacharide so Lac- means it cannot metabolize lactose. What does this mean within the context of the problem and how do I use it to decide that III will grow on the plate?

Okay, so what they're saying when the use Arg (+) or Arg (-) is whether or not the cell can synthesis arginine or not (I know that you've figured this out already, I'm just stating it for others). III can also grow on plate D b/c the plate contains both of the amino acids that it can't synthesize and glucose for fuel--it's inability to utilize lactose as a fuel is irrelevant in the presence of glucose b/c glucose is the preferred fuel of cells (easiest to use). Again, I'm not a microbiologist, so it would be nice if someone who is would double check me here!

Dr. Leonardo Noto
www.leonardonoto.com or follow me on Twitter @DrLeonardoNoto