What is the origin of plasmids?

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As I understand it, plasmids, like mitochondria, have their own genetic material and are capable of self-replication.

According to Wikipedia: Plasmids are considered replicons, units of DNA capable of replicating autonomously within a suitable host. However, like viruses, they are not classified as life. Plasmids are transmitted from one bacterium to another through conjugation. Unlike viruses, plasmids are "naked" DNA. However, some classes of plasmids encode the conjugative "sex" pilus necessary for their own transfer.

My understanding of that is that a bacteria gets their plasmids not because of the replication of their circular chromosome, nor because that chromosome have genes to code for the plasmid (I don't really know if that's possible), but because of the self-replication of their own plasmids.

So, my question is how the first plasmid got into the first bacteria, if they are not in their chromosomes? Were they a virus other prokaryotic cell that had circular DNA, and got phagocytosed by that bacteria ?
 

pinball1970

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As I understand it, plasmids, like mitochondria, have their own genetic material and are capable of self-replication.

According to Wikipedia: Plasmids are considered replicons, units of DNA capable of replicating autonomously within a suitable host. However, like viruses, they are not classified as life. Plasmids are transmitted from one bacterium to another through conjugation. Unlike viruses, plasmids are "naked" DNA. However, some classes of plasmids encode the conjugative "sex" pilus necessary for their own transfer.

My understanding of that is that a bacteria gets their plasmids not because of the replication of their circular chromosome, nor because that chromosome have genes to code for the plasmid (I don't really know if that's possible), but because of the self-replication of their own plasmids.

So, my question is how the first plasmid got into the first bacteria, if they are not in their chromosomes? Were they a virus other prokaryotic cell that had circular DNA, and got phagocytosed by that bacteria ?
Originally from another prokaryote I would have thought as per the mitochondria
 

pinball1970

Gold Member
505
425
As I understand it, plasmids, like mitochondria, have their own genetic material and are capable of self-replication.

According to Wikipedia: Plasmids are considered replicons, units of DNA capable of replicating autonomously within a suitable host. However, like viruses, they are not classified as life. Plasmids are transmitted from one bacterium to another through conjugation. Unlike viruses, plasmids are "naked" DNA. However, some classes of plasmids encode the conjugative "sex" pilus necessary for their own transfer.

My understanding of that is that a bacteria gets their plasmids not because of the replication of their circular chromosome, nor because that chromosome have genes to code for the plasmid (I don't really know if that's possible), but because of the self-replication of their own plasmids.

So, my question is how the first plasmid got into the first bacteria, if they are not in their chromosomes? Were they a virus other prokaryotic cell that had circular DNA, and got phagocytosed by that bacteria ?
A quick search has given me a few things but they are quite old.
One from Leeuwenhoek 1998
What have you found?
 
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202
IMHO, the recent discovery of mega-viruses, including some with size and/or genetics bigger than small bacteria, suggests 'Life' definition needs to be loosened.

Is pollen alive ? Not without a female flower. So, akin to a virus or phage...
Spores ? Yes, as self contained...

Tricky.
Looks like the origins of 'life as we know it' were even more of a 'free for all' orgy than 'tis yet comfortable to admit.

Modern parallel may be 'lichen', which is, wiki-quote, 'a composite organism that emerges from algae or cyanobacteria living among the filaments (hyphae) of the fungi in a mutually beneficial symbiotic relationship.'

IIRC, recent research suggests many lichens have a third, previously unsuspected team-member, yeast. This is also a fungi, but has evolved a rather different life-style...

Whatever, IIRC, several lichens' components seem well along to losing their independence, discarding 'surplus' genetic function, perhaps evolving towards what far future might consider akin to 'plasmids'....
;-)
 

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