Tuesday, June 14, 2011

Do Bacteria Have Sex?

In my previous post, I wondered if bacteria have gender; do they come in male and female versions? I'm still not sure, but they nonetheless engage in "bacterial conjugation" or what this biologist calls "DNA swapping."
"DNA swapping is my picturesque terminology to describe the fascinating and strange ability of bacteria to behave as if they are a super-organism comprised of different cell types instead of just different species of single-celled organisms. Basically, bacteria do not respect conventional species concepts. By this, I am referring to their habit of sharing small segments of their DNA with neighboring bacteria, regardless of "species". Because bacterial DNA swapping is different to what we see when parents provide copies of their DNA to their offspring (vertical gene transfer), this process has another name: horizontal gene transfer. More than simply hybridising a horse with a donkey to create a sterile mule, bacterial "species" that are as different from each other as a human and a parrot can share select segments of their DNA and still be capable of reproducing.

Bacterial conjugation is where one bacterium -- the donor -- transfers DNA to another bacterium -- the recipient -- using a "sex pilus" (the word "pilus" is misspelled in the above diagramme). But conjugation is not identical to sexual reproduction because, instead of sharing half its genome with its offspring, donor bacteria only transfer a small segment of DNA to recipient bacteria -- which are not its offspring. This small segment of bacterial DNA is not contained within the bacterial genome at all. Instead, it is a small ring of extrachromosomal DNA known as a "plasmid". Plasmids do not contain any of the hundreds of basic housekeeping genes that are essential for life. Instead, they contain just a few "extra" genes that may come in handy under certain circumstances; genes such as those encoding resistance to a particular type of antibiotic, for example.
Almost like miniature stamp collectors, bacteria are avid collectors and hoarders of plasmids. Further, they are not picky about the sorts of DNA they acquire nor are they particular about the plasmid DNA's source. Friendly gut-dwelling E coli can pick up genes that, in a Jekyll-and-Hyde scenario, can transform them into little monsters that are harmful or fatal to their hosts."
- Food Poisoning Reminds Us That Bacteria Do Have Sex, The Guardian, May 30 2011
It looks like the plasmid in the diagram encodes for a pilus?

This reminds me of the DNA swapping that goes on when we eat genetically engineered food. The authors of the study in my post GMO-Fed Livestock Incorporate Foreign GMO Genes Into Their Own Tissues said:
"This study confirms that feed-ingested DNA fragments (endogenous and transgenic) do survive to the terminal GI tract and that uptake into gut epithelial tissues does occur."
It wasn't just the colon, they found the foreign DNA in the animals' liver and kidney too, which infers some systemic travel. It made me wonder how much foreign DNA gets incorporated into our tissues when we eat genetically engineered food. And would that DNA then be capable of manufacturing the very pesticides for which it was designed?

Why won't the US require that genetically engineered foods be labeled? Europe does.
Image: Adenosine/Creative Commons Attribution-Share Alike 3.0 Unported license.


Claudia said...

Is there a reason why we're not labeling GMOs?

Bix said...

Well, the FDA says it's because they're no different from conventional plants.

Dr. Mel said...

This is fascinating! Who knew?!

Anonymous said...

That's not gender, that's sex.