Every morning, millions of people voluntarily enter a place teeming with bacteria and fungi. Despite the presence of so many microbes, we emerge from this place feeling clean and ready to start the day. What am I talking about? The shower, of course!
Now, it might not be all that shocking to you that your shower is a haven for microbial life. You have probably periodically noticed mold in the folds of the shower curtain and other places. This isn't news to you. But the shower provides a great example to illustrate how the microbes grow. If you have seen pictures of bacteria and fungi before, they are often portrayed as a loose collection of individual cells, typically floating around in a liquid environment. BUT...research is proving that microbial life in nature is not that simple. In the case of your shower, a research group led by Norman Pace (who is famous for other, non-shower-related discoveries) recently published two papers showing that an incredible diversity of microbes are growing in household showers in something called a biofilm.
As it turns out, this isn't unique to your shower. Microbes in nature frequently grow in biofilms. A biofilm is basically just like it sounds...it is a film or mat of microbial cells held together by substances that the cells themselves secrete. Although some biofilms are made up of only one species of microbe, many biofilms include multiple different species. This is really fascinating, because it suggests a level of multi-cellular organization across microbial species. Here are a couple of great micrographs of biofilms...
One of the key features of a biofilm that distinguishes this lifestyle from free-floating individual cells is the presence of an extracellular matrix secreted by the cells to hold the biofilm together and give it structure. This is the filmy substance that is especially visible in the bottom picture. The extracellular matrix can be made up of polymers such as proteins, sugars and even nucleic acids (DNA and RNA). These polymers give the biofilm a complex, three-dimensional structure, complete with water channels that act as a crude circulation system to move fluids and nutrients throughout the biofilm. Very organized, indeed!
Biofilms impact human beings in an incredible variety of ways. For instance, looking at those two pictures above, you might think, "Yuck! Both those biofilms look nasty. Let's get rid of them!" With the bottom picture, you would be right! The bottom picture shows a biofilm that formed inside the contact lens case of a person with a corneal infection. We definitely want to get rid of that biofilm. But...before we jump to conclusions, the top picture tells a different story. The top picture shows a biofilm that is involved in bioremediation, or the removal of a toxic compound from the environment by a biological life form. This particular biofilm is degrading perchloroethylene (PCE), a drycleaning agent and one of the most common groundwater contaminants in the United States. By organizing into a biofilm, the microbes are much more efficient at removing PCE from the environment. So...hooray for this biofilm!
And there's the catch with biofilms. There are a lot of examples of nasty biofilms causing harm. Quite a few bacterial infections are the result of a biofilm forming on the surface of a medical device, such as a pacemaker or a catheter. One frightening aspect of these biofilms is that microbes are often more resistant to antibiotics when they are in a biofilm than if they were free-floating. As a result, biofilm-associated infections can be particularly difficult to treat. In some cases, it seems like the extracellular matrix is providing a barrier against the antibiotic, but in other cases, we don't yet know why microbes in certain biofilms are more resistant to antibiotics.
But for all the examples of "bad" biofilms, we have a lot of examples of microbial biofilms doing good things for us humans. Most, if not all, sewage treatment systems in the U.S. rely on biofilms of microbes to remove and decompose waste in our sewage. Without the biofilms, the outflow from our sewage treatment plants would be pretty awful! And we already talked about how biofilms can be very efficient at bioremediation. Some researchers have explored how to clean up petroleum using microbial biofilms.
So, there you go! Isn't it amazing what we can learn about microbial life starting with something as simple as the shower? And now I really want to clean my shower.
Literature (for the interested):
Here's a great review of biofilms...
Do you always wonder what grows on your shower curtain? Check this out...
How about on the showerhead?
Micrographs were downloaded from MicrobeLibrary, sponsored by the American Society for Microbiology.
Credit for the top picture: Jennifer Bower and Ralph Mitchell.
Credit for the bottom picture: Louise McLaughlin-Borlace