Weird place on Earth Mono Lake in eastern California is where researchers found a type of bacteria that appears to break the rules for how we think life should survive. Credit: NASA image gallery

You may not know phosphorus when you see it, but your body does. Phosphorus is a sturdy workhorse element. In DNA molecules, phosphorus helps support the whole double helix. Within cells, energy shows up as ATP — and the “P” stands for phosphorus (specifically, phosphate, a form of phosphorus).

All life as we know it, in other words, depends on phosphorus. For that reason, scientists around the world were shocked December 2 when a team of scientists announced finding life forms that didn’t necessarily depend on this all-important element. In laboratory tests, the scientists grew bacteria that were able to use arsenic — a different element with similar chemistry — in the place of phosphorus.

It’s a surprising discovery because living organisms have never been found without all six of the ingredients crucial to life: carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur (all together known as CHNOPS). Arsenic, though, is a potentially fatal poison.

Many scientists say they would like to see more evidence that the research team did in fact observe life forms using arsenic instead of phosphorus.

“This is an amazing result, a striking, very important and astonishing result — if true,” Alan Schwartz told Science News. Schwartz researches chemistry at Radboud University Nijmegen in the Netherlands. “I’m even more skeptical than usual, because of the implications. But it is fascinating work.”

The bacteria came from Mono Lake, a lake in eastern California that is well known for its unusual population of living organisms, including shrimp and algae. The lake doesn’t drain, so the only way for water to leave is through evaporation. As a result, the lake is much saltier than the ocean.

An up-close picture of the bacteria GFAJ-1 grown on arsenic. Credit: Jodi Switzer Blum, NASA

Several researchers had been studying a number of tiny organisms that lived in Mono Lake mud. Astrobiologists study life in the universe and want to know how it started, how it has changed, and what will happen to life in the future. They also want to know whether life exists on other planets and if so, what it might look like. Many astrobiologists study what lives in Earth’s strangest places, such as Mono Lake, as a way to understand the possibilities for life.

The study was led by Felisa Wolfe-Simon of NASA’s Astrobiology Institute and the U.S. Geological Survey in Menlo Park, Calif. She and her team removed organisms from the Mono samples and grew those bacteria in the lab. The scientists fed the microbes with sugar and vitamins — but left out phosphate. Then they changed the diet again, and gave the microbes arsenate, which is a form of arsenic.

In one type of bacteria, called GFAJ-1, the researchers observed that arsenic wasn’t fatal. The bacteria continued to grow, though not as fast as if they’d had phosphorus. After studying these bacteria, Wolfe-Simon and her team concluded that the organisms had begun to make use of the arsenic the way they usually used phosphorus. The researchers suggest that arsenic was being used as a building block in the bacteria’s DNA.

“This microbe, if we are correct, has solved the challenge of being alive in a different way,” Wolfe-Simon told Science News.

If the scientists are right, then “life as we know it” may not include all the life that actually is possible. For astrobiologists, that conclusion suggests that life on other planets may not necessarily look like life on Earth.

It’s possible that follow-up studies will show that the researchers were mistaken. Wolfe-Simon and her team could not get rid of all the phosphorus when they were growing the bacteria. Some scientists say minute amounts might be enough to keep the microbes alive. It’s possible that, in the experiment, the bacterium GFAJ-1 was still getting small amounts of phosphate.

Can life exist using poison instead of phosphorus? Life of a different type is an exciting prospect, so stay tuned to see how the scientific community reacts. Next up, scientists will want to know how, exactly, the arsenic substitution works.

POWER WORDS

arsenic A highly poisonous metallic element having three allotropic forms, yellow, black and gray, of which the brittle, crystalline gray is the most common. Used in insecticides.

phosphorus A highly reactive, nonmetallic element occurring naturally in phosphates.

DNA A nucleic acid that carries the genetic information in the cell. DNA consists of two long chains of nucleotides twisted into a double helix and joined by hydrogen bonds between the bases.

molecule A group of like or of different atoms held together by chemical forces.

microbe A minute life form; a microorganism, especially a bacterium that causes disease.

bacterium A life form that is a single cell and too small to see without using a microscope. Bacteria (plural of bacterium) live in almost every environment on Earth, including very cold places, very warm places, in all types of water, in the air, even on and in plants and animals. These microorganisms can also cause disease in plants and animals.

Now, scientists say the microbes that live on our hands could be useful in a surprising way: fighting crime.

When police visit the scene of a crime, they often look for fingerprints to try to identify the culprit. They can also look for other things, like hair, to figure out who was there. But according to a recent study, investigators could even use microbes to help crack a case.

Every person has his or her own set of microbes that live on their hands, according to scientists at the University of Colorado at Boulder. That means that if you and your best friend were able to see and compare all the microbes that lived on both of your hands, your hands probably would look different. Some microbes would show up on your hand; others would live only on your friend’s hand. Your mix of different kinds of hand microbes is unique — much like your fingerprint.

The scientists in Colorado wanted to know whether this microbe mix could be used as a new kind of fingerprint — especially in a crime scene where fingerprints might be hard to find. The use of science to figure out what happened — such as studying fingerprints — is called forensics.

In the study, the mix of germs on each person’s keyboard matched the unique mix living on that person’s hands.

bluestocking/iStock

Noah Fierer, one of the scientists, says microbe fingerprints are harder to hide. “You only need to smudge a fingerprint, but you can’t sterilize a surface just by wiping it off,” he told Science News.

Fierer and the team of scientists knew that when people work on a computer, the microbes from their hands end up on the keyboard. (Think about the microbes that are on your keyboard — especially if many different people use it!)

So to do their experiment, the scientists compared the bacteria on the hands of three people to the bacteria found on each person’s computer keyboard. For the study, the keyboards had been used only by the people who were being tested. The mix of microbes from each person’s hands matched the mix of microbes on that person’s keyboard. The scientists were easily able to tell the three people apart — just by looking at their keyboards.

But that experiment was only on three people, so the scientists knew they had to test their idea against a larger population. Their next step was to collect bacteria samples from the palms and computer mice of nine people. When they compared those samples to the known microbe mix from the hands of 270 other people, the team again found a match. Nine times out of nine, the bacteria patterns lined up — and it was again easy to tell who had been using which mice. (The information on the microbe mixes from 270 people already existed as part of the Human Skin Microbiome project. The microbiome is the population of microbes that live in and on the human body.)

So far, so good — but there are a lot more than 270 criminals out there. Other scientists wonder whether the microbe fingerprint can really be that useful. “Right now we really have no idea how unique a person’s skin microbiome is,” Elizabeth Grice told Science News. Grice is a geneticist at the National Human Genome Research Institute, part of the National Institutes of Health in Bethesda, Md.

Fierer agrees that scientists have a lot more work to do before the microbe fingerprint will be a useful tool.

In any case, it’s something to think about. Even if you don’t leave your fingerprints behind, your microbes may give you away.

Going Deeper:

Sanders, Laura. 2009. “Bacteria flourish in favorite ecosystems on the human body,” Science News, November 5. http://sciencenews.org/view/generic/id/49242/title/Bacteria_flourish_in_favorite_ecosystems_on_the_human_body

Sohn, Emily. 2008. “Cell phone tattlers,” Science News for Kids, March 12. http://sciencenewsforkids.org/articles/20080312/Note3.asp

Sohn, Emily. 2006. “Fingerprint evidence,” Science News for Kids, May 3. http://sciencenewsforkids.org/articles/20060503/Feature1.asp