The Language of Bacteria: Antibiotics and Genes
What if I told you that bacteria can communicate? With each other, with bacteria of different species (and thus, of a different “language”), and even with you?
Well, believe it or not, they can. Understanding this communication may hold just the elixir we need to fight back at the modern threat of “superbugs” – bacteria that don’t respond to antibiotics. In recent years, doctors have been only able to treat such infections by reverting to pre-WWI treatments. For example, a young man who got a scar infected with MRSA in India ended up losing a leg as doctors tried desperately to remove the bacteria from his body. If the bacteria have infected an organ, well then, that organ needs to go too, before something else gets infected. If bacteria don’t respond to antibiotics, there is little we can do to fight them, advanced medical society that we are. And that is why understanding how bacteria communicate may end up saving countless lives as these superbugs continue to rise – in number and distribution around the world.
Understanding how bacteria communicate begins with understanding bacteria. Bacteria are single-celled organisms, and their cells are much smaller than plant or animal cells. While plant and animal cells have lots of little organelles in them – one for storing DNA, one for energy production, one for breaking down toxins, etc. – bacteria have no such organelles. Instead, they have a clump of DNA and other genetic material in the center-ish region of their cells, and a few ribosomes and proteins scattered throughout. They also have an outer membrane that is made of phospholipids. There are lots of other things scattered throughout this membrane. We’ll learn about one type of intermembrane protein, receptors, in the next essay.
Bacteria reproduce through mitosis, which is essentially chopping itself in half, then growing back to size again. Bacteria can replicate their genetic material, pinch off at the middle, and separate into two exact copies of themselves in as little as twenty minutes. While external factors such as temperature, acidity, and humidity can all factor in to how fast bacteria reproduce, when in their optimum environment, they typically do so rapidly.
Now, if all bacteria reproduce by simply copying their DNA, keeping one copy, and passing the other copy on to a daughter cell, they should have very limited gene pools. After all, sexual reproduction – which allows for a mix-and-match of DNA from two individuals – is a major player in producing all the incredible diversity we see among plants and animals today. Although bacteria only reproduce by essentially cloning themselves (that is, asexually), they still have a few tricks up their sleeve to increase genetic diversity among their clonal populations.
First of all, bacteria can gain genetic material via transduction. This is a fancy term for the injection of DNA from viruses. This can be in the bacteria’s best interest, or against it. For example, beaches often contain bacteria that cause cholera in humans. However, there is also a virus in those waters that puts lethal genes into the cholera-causing bacterial cells, and there’s never enough to get you sick after spending time in the surf. Another bacteria lives at the surface of the ocean and constantly is bombarded with UV rays, which kills much of its DNA. These bacteria would die without another virus constantly replenishing the cells with new genes to fill in the gaps.
Another way bacteria can gain new genes is through transformation. Transformation occurs when a bacterium that has good genes dies. You’d think that after a bacteria’s death, its genes would be conscribed to death too. But instead, after it dies, the DNA will break into individual genes and float out into the environment. We don’t know how, but the rest of the bacteria population seems to know which of those genes they need, and which they don’t. They know which genes from their deceased friend will help them, and which aren’t necessary. Once they’ve decided which genes they want, they can pick them up and incorporate them into their own genome.
A final means of obtaining genetic material is through conjugation. The DNA in bacteria can sometimes exist as plasmids, which are little circles of genes. These plasmids can be copied and given from one living bacterium to the next. It’s as if someone said, “You’re going through a hard time right now? I’ve been through the same thing. Here, how about I give you a copy of one of my genes? It really helped me when I was stuck in your position, and it can help you too.”
Now that we know how bacteria are capable of mixing up their genetic material, let’s consider how they evolve. That’s right, bacterial populations can change in response to environmental stimuli. One such stimulus is exposure to antibiotics. Many antibiotics work because they interact with an enzyme bacteria naturally produce. Most bacteria need this enzyme to help them function and stay healthy. Some bacteria, however, possess a gene that prevents them from producing that enzyme. Usually, such bacteria are seen as having bad genes in this respect, so they’re likely to try and pick up a plasmid that will enable them produce that enzyme. However, if you throw antibiotics into the mix, a reverse survival advantage occurs. The healthy bacteria that were producing that enzyme suddenly die from antibiotics because the enzyme and antibiotics mixed together in a deadly reaction! The unhealthy bacteria that didn’t get that enzyme-making gene are unaffected. Suddenly, they are the fittest bacteria in the environment, and every other bacterium there wants a copy of their enzyme-defective gene.
It is now obvious why superbugs are so dangerous. All it takes is one superbug to enter your system, and if you are taking antibiotics, every bacterium on and in you (including your good bacteria!) will turn to the dark side and get a copy of the superbug’s resistance genes. Transformation and conjugation can occur across species (since bacteria reproduce asexually, we have a hard time defining what a bacteria “species” is anyway). Get one antibiotic resistant bacteria in the wrong place, at the wrong time, and none of your bacteria will respond to antibiotics.