In response to the enthusiasm about the last biotechnology-oriented Microbial Monday blog post, today we will be talking about how scientists maintain the cells that they work on. To the delight of many comic artists, the process scientists use for this is known as: culturing.
Oftentimes when I explain my PhD project to people, they exclaim something along the lines of, “Wow, that must be so exciting!!” They are totally right – science is the best, and I wouldn’t want to be doing anything else. But I also don’t want them to get the wrong idea and think that being in the lab means having eureka moment after eureka moment. Therefore, my usual response to their enthusiasm is something like, “10 percent of the time it is super exciting, but the other 90% of the time it’s mostly pouring stuff back and forth between bottles.” This statement is especially true when you are busy with culturing cells – be it human cells, bacterial cells, yeast cells, or otherwise.
You see, the basis of cell culture is just about food and comfort. A simple rule applies to pretty much all living things: when the environment provides a perfect temperature and plenty of good eatin’, stuff grows. This is just as true for visible-to-the-naked-eye, multicellular animals like us humans, as it is for individual microscopic cells.
So, this is how we do it: We start with just a few cells. These cells might be taken directly from an animal - from a tumour, for instance, if you want to grow animal cells, or maybe from a bacterial infection, if you want to grow bacterial cells. The cells can also be harvested from the environment – for instance, maybe you want to grow (“culture”) a specific fungus that you have found growing outside. In my case, to be totally honest, these first few cells usually come from the lab's -80°C freezer, where some kind previous PhD student or post-doc has frozen away some sample to be used by all those who come after her or him.
Next, we give these first few cells a nice cozy home. This simply means that we pour them in a bucket with liquid food containing lots of vitamins, proteins, sugars, and salts, and then stick that bucket in an incubator that’s set to their favourite temperature. For human cells, and also for bacterial cells that are capable of infecting or co-existing within humans, that temperature is usually 37°C. This is no coincidence. 37°C is the average body temperature of a healthy human, so it makes sense that human cells like that temperature. So why do pathogenic (i.e. infectious) and microbiome bacterial cells like that temperature? Because they have adapted to make humans their home! 37°C is just room temperature for these bacteria.
Now, just like humans on cozy warm, food-rich planet Earth, cells grow like crazy in these cozy, nutrient-rich buckets. As long as they have plenty of food, warmth, and an absence of predators (i.e. they aren’t naturally killed by anything else in the bucket – which is what we aim for as scientists, although sometimes sneaky viruses or other predatory bacteria sneak in to our cell buckets) the cells will keep on growing - until they multiply themselves into a problem. This problem which I speak of, is the problem of overcrowding.
At some point, there will be so many cells in the bucket that there is no longer enough space or nutrients for them to keep growing. At this point, two things will happen. First, the cells will stop multiplying. Secondly, the cells will start dying.
The goal of cell culture is to keep cells out of this death phase. It sounds complicated, but the principle is pretty simple. All you have to do is take out some of the cells in the first bucket, and stick 'em in a new bucket, like in the super scientific diagram below.
And there you have it: that's pretty much all there is to culturing cells! In summary, hereby I present to you my three rules of successful cell culture:
1. Keep your cells at the right temperature. I take them out of the incubator for as little time as possible.
2. Keep your cells growing: don't let them get over-crowded or under-fed. Practically, this means that I'm regularly checking under the microscope as to how my cells are growing.
3. Assume that everything you haven't doused in ethanol will definitely infect and kill all of your cells. I obsessively clean off my bottles of cell-food (we call this "medium" in the lab) and basically everything else that will come near by buckets of cells (we actually call these "flasks" in the lab, but they are basically buckets with a fancy lid with a filter) to avoid any infections.
So, until next week - act like a cell. Stay warm, well fed, and cultured!
~ Alex