Why Do Plasmids Exist in Bacteria?

[Dr. Nick]

I’m a little bit confused with plasmids. I understand how they work replicate and function, but I can't say why do they exist ?

What is plasmid role, what is so special they do so they are worthy of existence? Almost every plasmid feature is “supported” by bacterial chromosome. Why when and how plasmid segregated form bacterial chromosome, why bacteria share their plasmids? They are unicellular organisms and they rarely benefit form from other cells (they help survive with plasmid) ?

p.s. many what, why, how, when... I couldn’t help, it sorry

 

[iansmith]

What is plasmid role, what is so special they do so they are worthy of existence?

The only answer that cover every plasmid DNA is the selfish gene theory.

There is plasmids that given special advantages to bacteria (ex: antibiotics resistance) but some do not have any apperant roles (ex: plasmid that have only one gene).

Almost every plasmid feature is “supported” by bacterial chromosome. Why when and how plasmid segregated form bacterial chromosome, why bacteria share their plasmids? They are unicellular organisms and they rarely benefit form from other cells (they help survive with plasmid) ?

Not all plasmid have feature supported by bacteria. Some plasmids support bacterial functions. Some large plasmid act as another chromosome. Some plasmid will have machinerires that iniate their replication

Plasmid are segregated during cell division. Segregation might be random (large copy numbers) or some have specific mechanism. Some have special DNA domain that ensure that the bacterial machinery segregate the plasmid. Some plasmid also produce a stable toxin and an unstable toxin that insure that every daughter cells will have a copy of the plasmid.

 

[quasi426]

Some plasmid also produce a stable toxin and an unstable toxin that insure that every daughter cells will have a copy of the plasmid.

I think you meant to say that some plasmids encode for expression of a stable toxin as well as an unstable ANTI-toxin or toxin inhibitor. That way if the bacteria lose the plasmid then the unstable ANTI-toxin will degrade and the stable toxin will remain around.