Scientists: Crab Blood Can Be Alien Hunter
July 9, 2003 -- One hundred million years before dinosaurs pounded upon the Earth, the humble horseshoe crab scuttled along its shores. Soon the blood of this primitive creature could be used to detect primitive life on faraway planets.
"One of the reasons the horseshoe crab has survived for so long is its advanced immune system," said Norman Wainwright, a senior scientist at the Marine Biological Laboratory (MBL) in Woods Hole, Mass. "This system can be used to find microbial life."
When one of these armored arthropods is injured, bleeding and exposed to bug-laden ocean water, its blue blood hardens and keeps infection out.
The crab's trick takes the form of a cascade of enzymes that causes clotting when it encounters cell wall material of most bacteria, yeast and mold.
Run By Freeze-Dried Enzymes
Since the 1950s, the unique coagulating reaction of the horseshoe crab's blood has been tapped by pharmaceutical companies to test the purity of sterilized medical equipment and products. Now scientists have packaged the blood's enzymes into a hand-held instrument that can test for signs of life.
"If there are microbial species that evolved outside the Earth, that life may have originated here and spread throughout the solar system," said Wainwright. "It's possible the cells walls of microbes on other planets may be similar enough to detect using the test."
The calculator-sized device developed by researchers at MBL and Charles River Laboratories in Wilmington, Mass., is filled with the unique set of enzymes contained inside horseshoe crab blood. To supply the tools, scientists insert a large needle into the crab's heart and extract up to 300 milliliters of blood per crab. The crabs are then released back into the ocean.
Although the process sounds traumatic, most of the helmeted animals survive the ordeal, says Robert Barlow, a State University of New York neurobiologist who conducts research on horseshoe crabs at the MBL.
"There's about a 10 percent mortality rate," he said.
The enzymes are then isolated from the blood, extracted and freeze dried. When inserted into the instrument, rather than coagulate blood, the enzymes cause a clear solution to turn bright yellow when encountering microbes.
"The more yellow the sample, the more microbes it's finding," Wainwright said.
Past Probes Tested for Life
Using the blood of one of Earth's oldest creatures may not seem particularly high-tech, but the test holds at least one key advantage over other methods — it's fast.
The horseshoe crab blood instrument has been used, for example, to ensure spacecraft are free of any Earthly microbes before heading to space and other planets. Once a swabbed sample is inserted, the instrument provides a reading within 15 minutes. Other tests that involve waiting for cultured samples to develop normally take three days or longer.
Barlow (who isn't involved in the project) says that MBL and Charles River scientists have volunteered their device to test the purity of spacecraft mostly to "get a foot in the door" at NASA so they might eventually send a unit to outer space.
Wainwright has even taken a microgravity flight on the so-called vomit comet (a modified jet whose pilot provides passengers with a sense of weightlessness by flying a parabolic course at high altitude) and found it functions fine with limited gravity.
The last time a Mars probe directly tested for signs of life was on board NASA's Viking 1 and Viking 2 crafts that landed on Mars in the 1970s. Neither of the probes' experiments, which tested for particular amino acids, produced any evidence of life.
The two NASA probes that are now on their way to Mars will mainly be searching for signs of water. The European Space Agency's Beagle 2, meanwhile, hosts instruments that will search the planet for signs of methane — a calling card of active life.
NASA officials say the two probes that will touch down in January 2004 are paving the way for future probes that will begin an aggressive search for life. It's on one of these spacecraft that Wainwright hopes the horseshoe crab blood instrument might catch a ride to the Red Planet.
Jason Dworkin, an astrobiologist at NASA's Goddard Space Flight Center in Greenbelt, Md., explains that because possible alien life remains mysterious in form, NASA will need an array of tests to seek it out.
"Life that we don't understand is difficult to recognize. It's hard to identify something if you don't know precisely what it is," Dworkin said. "So new tests are always useful."
Cutting the Catch
Of course, to guarantee the instrument is around when the next batch of probes rocket to Mars, scientists need to ensure horseshoe crab populations remain robust.
The horseshoe crab is undoubtedly a hardy creature — having survived 250 million years of evolution. The crab can go a year without eating and can endure extreme temperatures and salinity. But scientists say years of overfishing of the horseshoe crab for use as conch and eel bait have depleted the arthropods' numbers.
The Atlantic States Marine Fisheries Commission is now considering recommendations from a panel of scientists to cut harvests by more than half. The cuts will be considered in December and if approved, would apply from Virginia to New York.