Bacteria/Plasmid

I gave a lecture on bacteria the other day here in Camb and there were also additional materials which I dispensed for a wholesome learning experience. Anyway here is some tibits for the mind.

1) F factor = F plasmid

When you talk about F factor you are referring to the F plasmid itself. F factor is not a gene on the plasmid but represent the entire plasmid with the various genes that contribute to the particular characteristic i.e. having sex pilus.

2) F+ bacterium do not mate with F+ bacterium i.e. no mating bridge is formed between them.

Under normal circumstances, F+ bacterium with its pilus will bind to F- bacterium to draw them nearer to each other. This binding requires recognition of specific proteins on the F- bacterium which are missing in F+ bacterium. So once a F- bacterium receives a F plasmid, there will be changes in its surface proteins such that the above does not take place.

3) Additional: There are many other types of plasmids as well. There are some which confer tolerance to salinity, others produce toxins etc. However, there is one which I would like to talk about and there is the R factor.
R = antibiotic resistance
As the term implies, when a bacterium receives a R factor, it will become resistant to (specific) antibiotic. This is of course important in many of the laboratory work these days as well as the emergence of superbugs in hospitals.
There can be several types of plasmid in a bacterium. And some of these plasmids can make use of the mating bridge formed by the F factor to sneak into the receipient bacterium.