Re: Are the bacterial mats in Yellowstone harmful to people?

Dear Sonya,

Bacteria that cause health problems do so in one of two ways. The first way is through parasitism (by causing an infection). The second way is by producing compounds which are toxic if taken into the body accidently. First we'll consider the possibility that the famous Yellowstone thermophilic bacteria are infectious, and then we'll take a look at the possibility that they're toxic.

In order to gain access to nutrients, a parasitic bacterium must attach to its host's cells. Even if it lives in the intestinal lumen, the bacterium needs to attach to the surface of the intestine to prevent itself from being passed out of the body with the undigested food. To attach, the bacterium must have a specialized molecule on its surface which binds to normal receptors on cell surfaces. Our cells have these receptors to carry out their everyday functions, such as transporting ions and nutrients into and out of the body.

Different cells of the body have different receptors, because they're doing different jobs. If a parasitic bacterium has the ability to bind to a receptor that it bumps into, it will attach to the cell, and begin its infective stage. If, however, the bacterium doesn't have the ability to bind any of the receptors it encounters, it can't attach, and so it can't cause an infection.

The thermophilic bacteria in Yellowstone National Park live out their lives in an extreme environment far different than that of the human body. Floating in the steaming hot water, these bacteria have no need for molecules to bind human cell receptors, and so I would be very surprised to learn that they had them. Without those receptors, there is no possibility of infection.


Now let's consider the second way in which a bacterium might cause health problems in a human. Some bacteria produce compounds which are toxic to people when brought into our bodies. The bacteria get no benefit from producing the toxin. The toxin is usually just a metabolic waste product that the bacteria produces regardless of where it is. If the toxin is inhaled, ingested, or injected in large enough quantities, a toxic effect can occur.

One example of a potent bacterial toxin is endotoxin, which is released from inside the bacterium when it dies. This bacterial cell component just happens to cause sever illness, and even death, if released in large quantities inside our bodies. Another is botulism toxin, which causes botulism.

Do the thermophilic bacteria of Yellowstone produce such an accidental toxin? That's a good question. It's quite possible that they do. I haven't see a report of anyone fishing out the boiling bacteria and eating them, so I don't think anyone really knows!

To recap, bacteria can be harmful to human health in two ways: through parasitism and by production of toxins. The thermophilic bacteria living in the steaming waters of Yellostone National Park are probably not infectious because they probably don't have receptors to bind to our cells. It is quite possible that they produce toxins, and so you probably shouldn't eat them.


Thank you for your question, and if you have any more, please ask us!

John Carlson
MAD Scientist