Question: Origin of plasmids

Szatmari George szat at ERE.UMontreal.CA
Thu Oct 12 13:36:04 EST 1995

In article <45e13r$8rn at> Lesley Robertson <l.a.robertson at> writes:
>Steven Sanyal <steven.sanyal at> 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 
>>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.
>>steven.sanyal at
>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 
>Lesley Robertson

Just a quick note to add to this - I recall reading somewhere that
they uncovered some lyophilised Staph aurues cultures that were
orignially made in the 1920s or 30s - well before the widespread use
of penicillin as an antibiotic - and some of these S. aureus cultures
displayed resistance to penicillin.

George Szatmari
Dept de microbiologie
Universite de Montreal

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