Expert: Dana Krempels, Ph.D. - 2/12/2009

Question
Ok so this is a homework question but I'm not sure that I've come up with the correct answer. We don't have a book for this class so I've really thought about the answer. Please help me out here. The part of the question that I'm not sure about is: HOW ARE BACTERIAL STRAINS MADE? The answer that I have currently involves using transformation to insert the desired DNA into a plasmid--which can then be cut using restriction enzymes and ligated back together or simply replicated.

Answer
Dear Sheena,

Strains of bacteria are the same species with different genetic traits that allow them to be distinguished from each other.  Such traits include antibiotic resistance, inability to metabolize certain nutrients, etc.

Bacteria can evolve into different strains due to selection pressures, as in hospitals where their populations are subjected to constant exposure to antibiotics.  Those who have chance mutations that make them resistant to an antibiotic will be more likely to survive and reproduce, creating a strain that is different from the original.

It is sometimes possible to create a strain of bacteria with known genetic characteristics in the laboratory by inserting a plasmid or a vector that can cause insertion of a new gene into the bacterium's own chromosome.

Hope that helps.

Dana