Researchers examine this sea otter for clues to what might have killed it. Sea otters and other marine mammals sometimes fall ill from germs washed downstream and into the ocean. Credit: Calif. Dept. of Fish and Wildlife

Normally, doctors worry about how human illness will spread between people. But wildlife, too, can sometimes become infected with germs shed by people or their pets. And sometimes those germs may hit wild animals as hard — or harder — than they do people.

This is something that Melissa Miller has been studying for the California Department of Fish and Wildlife in Santa Cruz. As a veterinary pathologist, Miller studies animals to determine their cause of illness or death. She and her coworkers think of microbes as biological pollutants, which can harm animals in the wild. Human or animal feces — poop — are usually the source of these household germs that can wash into rivers and the ocean.

Natural wetlands can help slow the flow of polluted water. This gives beneficial bacteria in stream water the time they need to break down pollutants. But many communities have been converting wetlands to farms and residential areas. Now pipes and culverts move water quickly through what used to be slowly draining wetlands. The result, says Miller: Germs that typically live in land animals and people are sickening ocean mammals. These include sea otters, sea lions, dolphins and whales.

In the past few years, Miller and other researchers have discovered dead sea otters infected with a microbe called Toxoplasma gondii. This germ can cause nerve damage (including blindness) and retardation in people. It can cause deadly brain damage in otters. Miller and her coworkers now regularly examine the brains of dead California sea otters for signs of this infection, such as swelling and scarring.

Feces of infected land animals — typically wild and domestic cats — can spread the microbe. Feces and the germs they harbor get washed downstream and into the ocean. Clams, mussels, crabs and other filter-feeding animals can then ingest the germs. Animals that eat filter feeders can pick up the germ. “We think that is a big method by which sea otters are getting exposed,” explains Miller.

Sea otters can tell us a lot about the health of the environment, she says. One reason: These animals eat a quarter of their weight in food every day. Miller says that’s like a 160 pound person eating 40 pounds of hamburgers every day. Their large appetites and their living close to shorelines make sea otters particularly vulnerable to pollutants washed off of land. “What the otters are trying to teach us is that as much as we think [pollution] is going to go away, it actually just gets sent downstream and comes back to haunt us,” says Miller.

To help reduce sickness in wildlife — such as sea otters — keep pet cats indoors. In addition, seal pet wastes from litter boxes into bags before putting them in the trash. Towns near coastlines should also focus on preserving some natural areas as habitat for wildlife — and as a way to boost the breakdown of pollutants.

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.

Researchers have now found that microbes living under the ocean floor appear to produce propane and another gas called ethane. These microbes chew up ancient organic material, such as leaves and twigs buried in the sand, and they generate the gases as waste products.

That’s a surprise. Scientists had thought that propane and ethane could be produced only in the same way that petroleum is—by great heat applied to ancient, buried material.

Kai-Uwe Hinrichs examines a sample taken from a cylinder of sediment drilled out of the ocean floor.

Ocean Drilling Program Leg 201 Science Party

A team led by Kai-Uwe Hinrichs of the University of Bremen in Germany went on a research ship equipped with an enormous drill that dug out cylinders of sand or rock thousands of feet long. When the researchers examined these cylinders, they found traces of ethane and propane locked in the sediment.

Normally, to generate these gases, Earth’s heat cooks organic material in sand for many thousands of years. This can happen only at spots above cracks in Earth’s crust, where heat can leak out from inside Earth, and where thick layers of sediment would act like a blanket.

But the samples that Hinrichs and his coworkers had looked at contained thin layers of sediment. Some cylinders had also been obtained from places far from any cracks in Earth’s crust. So where could the gases be coming from?

Scientists already knew that microbes could break down organic material to produce a related, simpler gas called methane. So, undersea microbes were the only thing that made sense.

“When you can’t come up with any geologic source, then biology is an obvious candidate,” Hinrichs says.

The finding may someday lead to practical applications. Propane is valuable as a fuel, and ethane is used to make plastics. Pulling propane and ethane out of sediment is too difficult to be practical. But if scientists can better understand how microbes create the gases, they might be able to use the microbes’ methods to make ethane and propane directly from organic material.—J. Rehmeyer

Going Deeper:

Rehmeyer, Julie. 2006. Gassy bugs: Microbes may produce propane under the sea. Science News 170(Sept. 30):213. Available at http://www.sciencenews.org/articles/20060930/fob4.asp .

You can learn more about propane at en.wikipedia.org/wiki/Propane and ethane at en.wikipedia.org/wiki/Ethane (Wikipedia).

Cutraro, Jennifer. 2006. Microbes at the gas pump. Science News for Kids (April 12). Available at http://www.sciencenewsforkids.org/articles/20060412/Feature1.asp .

Sohn, Emily. 2006. Plant gas. Science News for Kids (Jan. 18). Available at http://www.sciencenewsforkids.org/articles/20060118/Note2.asp .

______. 2004. Drilling deep for fuel. Science News for Kids (Sept. 29). Available at http://www.sciencenewsforkids.org/articles/20040929/Note3.asp .

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Harvesting Biogas from Manure
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