Question

(7) Auxotrophic mutations have been extremely useful to study a number of processes in Escherichia coli and other bacteria. a) Briefly define the term "auxotrophic." (3 points) b) Suppose you were given two unlabeled tubes, one that contains a tryptophan auxotroph and the other that contains an aspartate auxotroph. Design an experiment to determine which auxotroph is found in each tube. Draw and explain it. (5 points)

Answer 1

a.) An auxotroph is a mutant organism that has additional nutritrional requirement, when compared with parental organism from which it is derived.The reason for auxotrophy can be linked to mutation i.e, mutation in any hundreds of different genes (for example genes of amino acid ,nucleotide or vitamins synthesis) can cause auxotrophy,thus resulting in a requirement for amino acid,nucleotide,vitamins etc or combinations of any both in the growth of the organism.

b.) Suppose tube A is a tryptophan auxotroph while tube B is an Aspartate auxotroph.Take petri plate the 1st has tryptophan and other nutrional medium added to it while the 2nd petri plate has aspartae and other nutrional medium added to it. The amino acid as a matter for fact act as a source of Carbon and nitrogen sources.Now streak the petri plates 1st and 2nd simutaneoulsy with tube A and tube B auxotroph culture randomly and incubate it. Tube A culture should grow in petri plate 1st while Tube B culture should grow in petri plate 2nd. thus we can find out tube A is tryptophan auxotroph while tube B is Aspartate auxotroph.Figure below shows the procedure in details.

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