Question: Origin of plasmids

Lesley Robertson l.a.robertson at stm.tudelft.nl
Tue Oct 10 09:48:27 EST 1995


Steven Sanyal <steven.sanyal at utoronto.ca> wrote:
>I am a third year Molecular Biology student at the university of Toronto 
>and am also taking a microbiology course out of general interest.
>
>I am curious as to the proposed origin of plasmids.  I have heard that 
>bacteria can actually scavenge their surroundings for useful pieces of 
>DNA.
>
>Most plasmids I have come across thus far have dealt with antibiotic 
>resistance genes - used for selections.  Did these genes evolve only 
>since the advent of antibiotics this century, or is it believed that they 
>existed before?  ie: were their natural antibiotic agents that existed 
>before - a sort of interbacterial warfare.
>
>Steve
>
>steven.sanyal at utoronto.ca
>

Most, if not all, were probably already around in one form or another, 
but not necessarily dominant in the community except where selective 
pressures gave "owners" an advantage. Not only that, it doesn't have to 
be interbacterial "warfare" (although that does occur - look up 
bacteriocins) - penicillin is a natural product of fungi (although most 
precribed modern penicillins have been chemically modified - hence the 
term "semi-synthetic penicillin"). Indeed, the oldest known herbals 
describe the use of bread mould as a good way of treating infected 
wounds.
Lesley Robertson






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