Intimate Strangers

I'm scanning the science news this morning, and come up with 2 similar stories in Science and the New York Times. There's an effort out to identify the majority of the bacteria that live on human skin.

Ewwww, you might say, but not so fast.

These are, for the most part, commensal bacteria. Meaning, they live on and in us with no bad effects. In fact, we WANT them there. They physically block "bad" bacteria from hooking on for a ride. Or they can make the environment a less acceptable place for the disease causers to establish a place.

We peacefully co-exist with our bacteria. There are 10 times as many bacterial cells on and in each of us than there are human cells that make us up. We're talking trillions of bacteria. Each of us is an ecosystem unto ourselves. We are made up of multiple trillions of cells of many different varieties and biological kingdoms. The vast majority of the microbes in the world are beneficial or neutral. They break down waste products, provide us with vitamins, and make the world a much more habitable place.

But scientists are trying to understand what types of bacteria colonize human skin naturally. Scientists at the U.S. National Institutes of Health (NIH) are sampling different areas of the body to find out what average, healthy people carry. Strangely enough, they've discovered that the space between your toes is a barren wasteland for bacteria--they just don't go there. However, elbows, Some of them have been known, such as Staphylococcus aureus, which can be a disease causer, but not all the time. The NIH study has found that 90% of the bacteria they're finding belong to the genus Pseudomonas which is a common soil bacterium, but not known to inhabit skin before.

Moreover, the types of bacteria that are on us differ depending on where on the body you sample. So, the bacteria are picky as to what areas they inhabit. The bacteria on the inner elbow, for example, are of different species from the ones a few inches away on the forearm.

Now, why do they want to know which bacteria inhabit the skin? Well, beyond the fact of it's just good to know what you're dealing with, it might be good to find out at some point if the microbial content differs in people with skin conditions (such as eczema). If there is a difference, perhaps that information could be used for better treatments for those skin conditions.

For more information on this work, here's the link to the NY Times article on it. More links to follow if you're not registered on the Times site.

Bacterial Promiscuity

Promiscuous behavior abounds in the microbial world! Unknown to the world at large, bacteria regularly "have sex" and transfer DNA. We can get them to do it in the lab too (they're not too picky about mood and music).

You can see photos and movies (G-rated) here.

Basically, the bacteria make an appendage on their surface called a "pilus." It's a long hollow tube, and it can attach to adjacent bacteria. When that happens, DNA can transfer from one cell to the other. This is called conjugation. In basic microbiology labs we do conjugation experiments. You basically grow up 2 different strains of E. coli (usually we use a non-infectious E. coli for these experiments), mix them together in a tube, and let it incubate for various times--usually up to 30 minutes.

You can determine that conjugation has occurred because the recipient strain will have acquired a new trait that is easily tested for--such as antibiotic resistance.

In nature, conjugation and other forms of DNA uptake occur all the time. This is one major reason for the great increase in antibiotic-resistant bacteria. If bacteria are exposed to a sub-lethal dose they can develop resistance. This happens quite often actually--we can demonstrate it in the laboratory. Sometimes this resistance can be transferred to other bacteria.

And after a long time of this happening, you get things like MRSA Staphylococcus aureus that is resistant to many commonly used antibiotics. MRSA is the bacterium getting a lot of press recently--wrestling teams coming down with skin infections, schools becoming infested with it. It's a S. aureus that has acquired some new tools to manage to resist medical onslaughts that attempt to kill it. You can treat it with the right stuff.

This phenomenon of resistance is a major health issue. The bacteria are just doing what comes naturally. They're wonderful at adaptation, and to them they are just adapting to chemical onslaughts and sharing the information. It's only a problem when the bacterium doing the adjusting also happens to be a human (or plant) pathogen.

What's New and What's Cool?!?

I've been away for a bit. Busy doing writing of a different sort. But I've tried to keep up on things.

So, what have I seen that I thought was interesting?

I watched a Nova episode from 2006 on PBS last night on the exploration of Saturn and its moon Titan by Cassini and the Huygens space probes. Fascinating stuff. Titan is one of only 4 known bodies in our solar system that is rocky and has an atmosphere. The other three being Earth, Venus, and Mars. Venus is way too hot to have any organic molecules present (lead will melt on its surface), and Mars is far too dry. Titan is incredibly cold, but interesting in that it might give insights on what it was like on a very primitive Earth.

Pictures taken by the Huygens probe on Titan showed an alien yet somehow familiar surface. Structures looked like mountains, lake beds, and even volcanoes. However, the rivers are made of liquid methane. It's so cold there that what is gaseous methane on Earth is liquid there. And the volcanoes are actually cryo-volcanoes. When they erupt, they don't erupt lava, but they erupt a mixture of supercooled water mixed with ammonia. The temperature of this is about -100 degrees Celsius!

Methane is an organic molecule made up of carbon and hydrogen. Ammonia is made up of nitrogen and hydrogen. And water is present. These could potentially be building blocks of amino acids (chemicals that make up proteins). It's so darn cold there though, that any chemical activity takes a long time to happen.

So, who knows. Maybe deep down under Titan's surface where it's a bit warmer there are actually microbes down there. Here on Earth we have bacteria that release methane as a byproduct of their metabolism. Could something similar be going on there, deep under the surface of Titan? Could interstellar methanogens be present on one of Saturn's moons? Could those methanogens be responsible for a good portion of the methane on Titan? I'll probably never know in my lifetime, but it's fun to contemplate.

Back when I was in graduate school, taking my general exam, we were asked to think about this question. If there were life on another planet, it would probably be microbial. So for our test question we had to design a microbial ecosystem for this hypothetical planet. It's kind of fun to look at pictures of Titan taken by the Huygens probe, and think that my general exam might actually be playing out in real time somewhere out there.