Bacterial Conjugation

[hitmankratos]

Hi,

 

Why do bacteria share plasmids together? What pushes them to do that? Is it some way to multiply?

 

Thanks in advance.

[Cap'n Refsmmat]

It's not some way to multiply. It increases phenotype diversity by trading genetic material and making new combinations of genes.

[hitmankratos]

Yeah but why does the donor share his plasmids? What's in it for him ?

[ecoli]

Yeah but why does the donor share his plasmids? What's in it for him ?

 

There's some interesting evolutionary theories about this relating to game theory.

 

http://journals.royalsociety.org/content/940d0etwfy89njtu/

 

For virulence factors that are secreted extracellularly, selection within hosts may favour mutant ‘cheater' strains of the pathogen that do not produce the virulence factor themselves but still benefit from factors produced by other members of the pathogen population within a host. Using simple mathematical models, I show that if this occurs then selection for infectious transmission between hosts favours pathogen strains that can reintroduce functional copies of virulence-factor genes into cheaters via horizontal transfer, forcing them to produce the virulence factor. Horizontal gene transfer is thus a novel mechanism for the evolution of cooperation.

 

Translated in into english - enforcing social cooperation can help both parties if conflict can harm both parties.

 

I think there are some newer papers out now along these same lines.

[Mr Skeptic]

For the same reason that more complex species have sex -- to mix and redistribute genetic variation.

[hitmankratos]

ok great thanks everyone.

[CharonY]

The advantage is not only on the side of the bacterium, but that of the mobile genetic element itself, too.

 

From the viewpoint of the plasmid its fitness increases, if it can be persistent in as many bacteria as possible. As such it exhibits mechanisms that allows conjugation. It is the similar to, say, viruses. In contrast to viruses, however, plasmids do not exhibit a protein structure that enables them to infect cells. So, if the plasmids would actually decrease fitness of the cells (as viruses usually do), they would vanish, as there would be selective pressure on the side of the bacterium not to take them up, and the plasmid has no way of forced entry. As such generally only plasmids with contribute positively to bacterial fitness (e.g. resistance, metabolic or virulence plasmids), persist within a population.

 

In fact, mobile genetic elements (including viruses, transposons, plasmids etc.) are the purest example of egoistic genes. Either force the cells to to propagate you, or make it worthwhile for the cell to do so (and at the same time introduce means of propagating yourself).

[pioneer]

I think we are personifying bacteria. The reality is, the process may be closer to nothing more than chemical attraction leading to a lower energy state. It can't be a higher energy state or it would not be favorable.

 

One way to look at it is, selective advantage, implies higher efficiency or less lingering potential. If an animal can gather food better there is less lingering hunger potential. The body get what it needs faster making it more efficient. This efficiency gives it an advantage in that environment.

 

When two bacteria merge, both may have lingering potential, with the merger a way to lower potential. The transfer may help one or both, so the net system potential is lower and more efficient. Bacteria are not that intelligent but are a living pile of chemicals following energy laws.

 

That is why mutations tend to lead more toward progress than regression to a weaker state. Forward is more efficient and has an energy advantage. Random would generate selective disadvantage, i.e, more lingering potential, as fast as selective advantage, i.e., less lingering potential, which is not observed in nature. Things tend to more forward over time since this is the directions of highest efficiency and lowest potential based on what it has available.

[CharonY]

Nope.