Biofilms at 11

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...

How Does It Work?: Penicillin

In the grand tradition of great sites like HowStuffWorks.com, I decided to start a regular feature with the terribly derivative title How Does It Work?  Why?  Well, because microbiology isn't confined to textbooks or research laboratories.  We interact with microbes every day.  We are carrying them in our guts, on our skin, inside our nose (yes, gross but true).  We eat and drink things that microbes help produce (bread and beer, for example).  Sometimes they help us and sometimes they hurt us.  So, it makes sense for us to know a little more about the different ways we study them and how we try to control them for our own purposes.

For our very first How Does It Work? today, I'll talk about the antibiotic penicillin, which was one of the first antibiotics discovered and then mass produced for treatment of bacterial infections.  Penicillin is credited with dramatically reducing the number of military deaths due to infection during World War II.  Although penicillin itself is not often prescribed these days, there are a number of antibiotics derived from penicillin that are still used in clinical therapy today, and these antibiotics work in the same general way as penicillin.

So, what is penicillin?  It is a chemical compound that is naturally produced by a fungus called Penicillium.  Below is a great picture of what Penicillium looks like under a microscope; the long filaments are called hyphae and the broom-like structures sprouting off from the hyphae are made up of columns of round spores.

Many of our antibiotics are derived from compounds produced by fungi or bacteria.  These compounds are the result of an evolutionary arms race between the different microbes that occupy the same environments.  In the case of Penicillium, this fungus lives in the soil, and it evolved to produce penicillin as a way of competing against other soil-dwelling microbes for resources.  Scientists discovered that what works for Penicillium can also work for us to combat bacterial infections.


How does penicillin work?  This may not be something you think about when you take an antibiotic.  Usually, we're just happy to take a pill and feel better.  But when you take your first course of an antibiotic, an incredible, microscopic drama starts to unfold within you.  Here's how it goes...

Bacteria on the move

Have you ever seen a time-lapse video of people on a city block?  New York's Times Square, maybe, or the Embarcadero in San Francisco.  It's amazing to watch people weave in and out, following their individual paths.  This might surprise you, but the microscopic world often resembles that busy city block!  Many bacteria are motile, which means that they can propel themselves in a particular direction and even change directions.  Motility is very important to bacteria...and sometimes bacterial motility has serious consequences for us.

In the video below (courtesy of the wonderful MicrobiologyBytes Video Library), you can see an incredible range of motile bacteria.  

Notice the little elliptical cells, such as those shown at the beginning of the video. Although you can't see it in the video, these cells have one or more whip-like structures called flagella protruding from their cell surface.  Here's an image of a bacterial cell and its flagella.

Matters of size

We're used to thinking about bacteria as tiny invisible creatures, and for the most part that's true. However, the diversity of the bacterial world holds a bit of a surprise for us. There are giants among the microbes...in some cases, they are the size of the period at the end of this sentence. One such giant microbe was discovered off the coast of Namibia in southwestern Africa. It was named Thiomargarita namibiensis...this Latin name means "Sulfur pearl of Namibia". How big is this bacterium, and how did it get its beautiful name?

Let's talk about matters of size first. E. coli is a common bacterium used in laboratory studies, and it is a member of the microbial community in the human gut (yes, you are carrying E. coli around with you every day). A typical E. coli cell is about 1 micrometer (or micron) wide and 2 micrometers long. There are 1000 micrometers in one millimeter. Now, this is where I admit that I was never very good at visualizing the metric system without a reference of some sort. So, for comparison, a strand of human hair is about 100 micrometers thick. Below, I've drawn a comparison of the size of an E. coli cell and the size of a human cell. Human cells actually vary a reasonable amount in their size, but this is a fairly typical representative.

Not to tangent, but this size difference explains why your body can contain more bacterial cells than human cells (a point made in my introductory post). Now, let's bring out the giant! Below, I've changed the scale (compare the two bars in the top and the bottom drawings) to compare the same human cell to a Thiomargarita namibiensis cell. Look at this whopper!

It's huge! To make this point even more clearly, here is an incredible picture from the original article published about this bacterium (Schulz et al. Science 1999). The white glob at the top left of the picture is a Thiomargarita namibiensis cell. A single cell! For comparison, it is laid out next to a fruit fly.

That is one big cell. Cells of Thiomargarita range from as "small" as 100 micrometers in diameter to upwards of 750 micrometers in diameter. How can this be possible? It turns out that most of the interior of a Thiomargarita cell is occupied by a large sac called a vacuole where the bacteria store nitrate. Thiomargarita uses the nitrate along with sulfur from its environment to produce energy. Nitrate can sometimes be rare in their environment, so the bacteria have evolved a structure to hoard enough nitrate to ensure their survival.

So...our giant microbe gets its name from "Thio" = containing sulfur, "margarita" = pearl in Spanish, "namibiensis" = from Namibia....Thiomargarita namibiensis = "Sulfur pearl of Namibia". Looking at the picture with the fruit fly, I can see how this giant microbe looks like a pearl!

Primary literature:

Here's the original description of Thiomargarita.

Amazing bacterium protects the world from insect mummies!

Every so often, I run across some delightfully hideous tidbit of information that makes me think the best horror filmmakers in Hollywood can't hold a candle to the grotesque goings-on in the natural world.  Take the aphid.  This small insect lives on plants of all kinds, sucking out the sugar-rich sap and generally wreaking havoc on agriculture worldwide.  Fortunately for the farmers, and unfortunately for the aphids, these little insects are prime targets for parasitic wasps.  And this is where it goes all Alien.  A wasp will swoop down from the sky, land next to an aphid, and, in the blink of an eye, twist its body and stab the aphid.  It doesn't sting the aphid.  It's much worse than that.  In that briefest of seconds, the wasp actually deposits an egg instead of the aphid's body.  Now it's only a matter of time before the aphid has its John Hurt moment.  The aphid will continue on its merry way for a short while, but then, the egg hatches inside its body, and the wasp larva eats the aphid from the inside out to fuel its own development.  Eventually, all that is left of the aphid is a brown husk, and the mature wasp emerges by chewing its way out of the mummified aphid corpse.  Want to see this in action?  Check out this video from Nat Geo below (at 1:18 there is a particularly great shot of a wasp larva moving inside a mummified aphid corpse)..