In article <45e13r$8rn at mo6.rc.tudelft.nl> Lesley Robertson <l.a.robertson at stm.tudelft.nl> writes:
>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
>>>
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
