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Name: Strait J.
Status: Educator
Age: 50s
Location: N/A
Country: N/A
Date: December 2002


Question:
Will a bacterium take up a recombinant plasmid if it already has one? If not, where do scientists acquire bacteria without plasmids for the purpose of taking up plasmids that have been engineered with a human gene?



Replies:
A bacterium can take up several plasmids, provided these plasmids are 'compatible'. Plasmids contain certain genetic elements that prohibit the same host cell to take up other plasmids containing those similar elements, thus, they are incompatible. Sometimes it is required for the setup of an experiment that a bacterium contains two different plasmids, and that can only be done if two compatible plasmid types are chosen.

In most cases, the receptor host bacterium, say E. coli, is free of plasmid at the beginning of the experiment. Such well-characterized plasmid-free strains are available from (commercial) strain collections. Wild-type strains collected from the environment or from animal/human hosts frequently contain plasmids. There are experiments available to 'cure' the bacterium from the plasmid (select for cells without plasmids) but this is not always successful, especially when the advantageous properties of that plasmid are not known.

Trudy Wassenaar
curator of the Virtual Museum of Bacteria
www.bacteriamuseum.org



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