In article <45jn6k$qcm at epervier.CC.UMontreal.CA>, szat at ERE.UMontreal.CA (Szatmari George) says:
>>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
>>True, but also remember that plasmids have their own mechanisms for
spreading laterally, that is, by conjugation to other bacteria. And
they don't like competition from related plasmids either:
incompatibility. What it all adds up to, is that plasmids sort of
have a life of their own, too. They are not only just tools for
their "host" bacteria - although they are that too.
Could one say that they in a way are symbiontic "viruses"?
And about the scavenging of DNA - that would be transformation, and
it has been shown to occur naturally only in some bacteria (the classic
encapsulated Strep. pneumoniae experiment).
Monica
