Shuffling the deck: Integrons and resistance genes

Maybe the reason I like bacteria so much is that they remind me of little machines. They float around and perform a lot of different functions that keep them alive. Within bacteria, there are also some random processes that occur, (like mutation or recombination). Sometimes these processes benefit bacteria, but most of the time they don't. When the processes go badly, the bacteria that experienced them dies, or gets replaced by bacteria that can grow more rapidly, or use resources more efficiently, or survive longer or whatever. This is no big deal to bacteria because they are clonal, and there are about a zillion more just like them except without the deleterious change. However, if the random event is beneficial, then the payoff is huge. The altered bacterium will rapidly take over the population and dominate it's little microbial world.

Integrons are like decks of cards in bacteria except that instead of cards, they are decks of resistance genes. They are all lined up in one cohesive stretch of DNA and they are linked to each other. Integrons are one way that bacteria can become resistant to lots of antibiotics all at once. The problem with integrons (for bacteria) is that mostly bacteria can only play the first card in the deck meaning that they can only efficiently express the first gene in the integron. If the bacteria are exposed to an antibiotic that they have a resistance gene for, but that resistance gene isn't the first one in the integron, it won't do them much good, because they can't express it. However, just like cards in a deck, the bacteria can shuffle the resistance genes in an integron and reorganize the order they are in. This enables them to change which one is first.

Just like shuffling a deck of cards, shuffling the genes in an integron occurs randomly. However, because bacterial clones usually divide pretty rapidly, there are lots of bacteria that have the integron. When they shuffle their resistance genes, odds are that most of them will end up with the wrong resistance gene in the first position. However the odds are that some of them will end up with the right resistance gene in the front of the deck. Those bacteria will take over the population and go on to cause more infections another day. Now of course I hate the infections they cause, but the way they survive is pretty neat.