Is that a pilus on your surface, or are you just happy to see me?
Sitting here reading this, you are probably unaware that bacteria might be performing their own version of sex somewhere near you! That’s right, bacterial orgies could be happening in your body right now, without your consent!
But of course, bacterial “sex” isn’t equal to that of humans. When humans… ahem… do it… DNA is transferred from the man to the woman in the form of sperm. The woman doesn’t take and hoard the DNA from every male partner she’s had, instead the DNA is combined with her own to form a child. Bacteria also like to share DNA when they get down and dirty, but they have no interest in forming offspring. They call it horizontal gene transfer, not because the bacteria do it lying down, but because the DNA is taken up by the recipient and not used to to form offspring (which would be vertical gene transfer).
Bacteria can share DNA in several ways, and my favourite is through a mechanism called bacterial conjugation. Say there are two bacteria, Bob and Betty. Bob has a rather unique piece of circular DNA, called a plasmid, and he really wishes to share it with Betty. He also has something else Betty doesn’t have: a hair-like appendage known as a pilus (check out Bob’s pilus below). If Bob gets close enough to Betty, he can latch onto her using his pilus. With this pilus, he can draw Betty and him closer together so they are touching.
Now the fun begins.
Bob starts to replicate his plasmid, making a copy for Betty. He then sends the plasmid over to Betty so she can have her own. Bob and Betty decide they’ve had their fun and part ways. Sure it didn’t last long, but it was long enough for Betty. She got what she needed, and now she has little use for Bob. From her intimacy she scored genes she’d never had before, and even gained the ability to make her own pilus!
And now that Betty-turned-Bob has a pilus of his own, he isn’t going to be the recipient of any more plasmids. He just doesn’t role that way. But he’s more than willing to use his pilus to give some other lucky bacterium his abilities.
Unlike humans, who generally only share STIs when they engage in some unprotected action, the bacteria can share something much more pleasant. That’s right, Bob wasn’t a selfish lover; he is a firm believer of the sharing-is-caring mentality. The DNA he shared with with Betty contained genes for resisting common antibiotics. This is great news for Betty; she was quite worried about ampicillin and tetracycline.
But the news isn’t so good for humans. Thanks to conjugation, a bacterium can go from complete susceptibility to many common antibiotics to very resistant, all within a single generation. We don’t care so much about harmless gut bacteria giving each other antibiotic resistance. But when a bacterium that poses a risk to our health gets resistance through conjugation, it is quite concerning. This is just one more challenge amongst a myriad in the race against antibiotic resistance. And all because Bob couldn’t keep it in his pants.