Bacterial Reproduction

[MedPR]

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A particular bacteria is noted to have a small plasmid, which is identified as coding for a sex pilus. If this plasmid is removed from all of the bacteria in a colony, what can be expected of the colony?


A Reproduction would desist and the colony would naturally die out.
B Population growth would slow down.
C Mutations would have a much more harmful effect on the colony.
D Population growth would remain the same.

Answer is D. Explanation: The sex pilus is only necessary for conjugation (genetic recombination). It is NOT necessary for bacterial survival, thus population size would not be hindered. Mutations would have LESS of an effect on the colony, because there is less genetic recombination because there no longer exists a sex pilus gene.

I thought the sex pilus was necessary for initiating conjugation, so if you make a bunch of bacteria without sex pili, those bacteria cannot initiate conjugation with another bacteria, thus reducing the number of initiators and essentially slowing population growth?

Is this not the same as F factor?

 

[MT Headed]

Umm, bacteria reproduce via cell division. They split in half, making two copies of themselves. That's it.

Bacteria have several methods of incorporating or donating DNA, the sex pilus (via the F plasmid) being one of them. But that's just mixing DNA, and has nothing to do with reproduction nor the growth of the colony. If they never incorporated or donated DNA at all, they would still split and reproduce (asexually) just fine.

 

[MT Headed]

Insert obligatory EK Audio Osmosis reference where Jordan realizes that bacteria can have sex and it doesn't lead to making babies, and says 'well that makes bacterial contraception real easy'.

If you don't have EK Audio Osmosis, you really should check it out.

 

[BA11]

Bacteria reproduce via binary fission, which is the splitting of a single bacterium into two daughter cells. Conjugation is a means of transmitting genetic material from one bacterium to another. They are independent processes.

 

[MedPR]

So conjugation doesn't involve replication at all? Just transfer of DNA?

 

[MT Headed]

👍

Now go look up the other ways bacteria can get new DNA.

 

[milski]

Too late to dig in the textbooks, so let's try a random guess. Viruses/virii? (or whatever the plural of virus is)

 

[SaintJude]

Transduction (movement of genetic material from one organism to another via virus, like milski is saying)
Transformation (integration of foreign chromosome fragment into host genome)

Anyway, I actually wanted to thank you for the question--I would have def gotten that wrong.

 

[MedPR]

Transduction (movement of genetic material from one organism to another via virus, like milski is saying)
Transformation (integration of foreign chromosome fragment into host genome)

Anyway, I actually wanted to thank you for the question--I would have def gotten that wrong.

In your definition of transformation, by "host genome" do you mean "bacterial genome"? Transformation occurs when competent (basically alive, and able to incorporate outside DNA) bacteria pick up DNA from their immediate environment. For example, from other bacterial cells that were lysed but not completely engulfed (yet) by macrophages.

Transduction, as you say, involves exchanging or introduction of another bacteria's genome via a bacteriophage. For example, a bacteriophage accidentally engulfs a copy of bacterial DNA (instead of viral DNA) and upon infection of a different bacterium, injects that bacterial DNA. The old method of DNA replication was basically controlled transduction using a plasmid and some other junk that I don't remember right now. Obviously this was replaced by PCR.

 

[MedPR]

And yes, I'm glad I found this question too (mcatquestionaday). I would've gotten it wrong on the MCAT because I thought conjugation was somehow related to reproduction. Now I'll never forget it's only for genetic recombination 🙂