NORMAN Wainwright reaches into his aquarium tank and pulls out an otherworldly being. The horseshoe crab, her legs waving in alarm, looks both ancient and alien 鈥� a cross between a trilobite and a miniature Starship Enterprise. It is an odd combination, but remarkably appropriate. This is one of Earth鈥檚 oldest creatures, that has barely changed over the past 200 million years, and it is now being catapulted into the space age.
Wainwright has been studying these curious animals for more than a decade. Last year he took his research to a new frontier when he carried an extract of horseshoe crab blood with him aboard the Vomit Comet, the high-tech jet NASA uses to simulate zero gravity. While lurching through the atmosphere at high speed, he proved that a primeval defence system, the immune response of the horseshoe crab, can work in space. He is also proud and a little surprised to recall that he managed to retain his lunch.
Back on the ground in his lab at the Marine Biological Laboratory at Woods Hole, Massachusetts (MBL), Wainwright holds a wriggling horseshoe crab and gently inserts a needle into the space between her solid carapace and her tail, collecting a few millilitres of blood from a vein in her back. He adds the translucent fluid to a test tube containing bacteria and it changes from a nondescript, neutral shade to bright sky blue as the copper in the oxygen-carrying molecules oxidises. Seconds later as the crab鈥檚 immune system gets to work, it gels into a clot.
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Instead of the army of diverse immune cells that patrol our own bodies, the horseshoe crab, like many other marine invertebrates, has just one type of defensive cell, called amoebocytes. They travel to sites of infection where specific carbohydrates in the cell walls of yeasts, moulds and gram-negative bacteria prompt them to release a cascade of enzymes. These break blood proteins apart, ultimately causing a clot. In the wild, this system protects horseshoe crabs by sealing wounds and stopping microbial invaders in their tracks.
The same immune reaction is now also used in medical labs around the world to test for germs on surgical instruments, injectable drugs and medical devices. The limulus amoebocyte lysate assay, or LAL, was developed by scientists working at the MBL in the 1960s and 70s. Amoebocyte enzymes activated by microbial contamination slice apart a synthetic peptide, which then turns yellow. The intensity of the colour, read by a spectrophotometer, reveals the number of microbes present. Over the past 15 years the test has become the basis of a bustling biomedical industry, which relies on blood harvested from wild horseshoe crabs. After a small amount of their blood is collected the animals are released. Although a few die through accidental injury or stress, Wainwright estimates that between 85 and 90 per cent survive the process.
The idea that LAL might be put to work in the space programme surfaced when Wainwright met John Rummel, who was working as the MBL鈥檚 director of research administration between stints with NASA. Rummel is now NASA鈥檚 planetary protection officer, and it is his job to keep the rest of the solar system free from earthly microbes. 鈥淭he whole point of the space exploration programme is to know if there is life on other planets,鈥� he says. 鈥淭he last thing we want to do is go to Mars to learn about micro-organisms from Florida.鈥�
With this in mind, as he explained to Wainwright, NASA sends in a squad of biologists to swab all the surfaces of a spacecraft as it is being built and then try to grow microbes from the swabs. But major delays can happen because the culture process takes three days. And if a sample comes up positive, three days of assembly work may have to be undone to access and clean the contaminated area. Worse still, only about 1 per cent of known microbes can be easily grown in culture, so if none of this select band is present, contamination will go unnoticed.
When Wainwright mentioned that horseshoe crab enzymes could detect a wide range of microbes in a test that gives quick results, Rummel encouraged him to apply the LAL assay to spacecraft construction. So in 1999, Wainwright made the first of many trips to the Kennedy Space Center. As crews worked to assemble the Spirit and Opportunity probes, ready for their journey to Mars, Wainwright searched for micro-organisms, comparing the results of traditional culture tests with those he obtained using LAL.
LAL has proved to be a great improvement on the traditional method. With a hand-held unit the size of a calculator it tests for microbes in less than an hour. But there is a downside: the technique reveals the presence of microbes without showing whether they are alive or dead. So culturing microbes remains part of the testing process.
Spirit and Opportunity are now scouting round the Red Planet looking for evidence of water, the most basic requirement for life. And NASA has plans to use LAL as part of a battery of tests to help sterilise the next generation of Martian probes. But ensuring that Mars and other planets do not become contaminated with earthly microbes is just half of Rummel鈥檚 remit. He is also responsible for preventing contamination of Earth with any extraterrestrial microbe that might prove to be a real-life Andromeda Strain.
In the next few years, NASA hopes to bring back samples of Martian rock and ice and analyse them for signs of life. If there is life on the Red Planet, it is most likely to be microbial in nature and NASA will need tests such as LAL to hunt it down. 鈥淚f there is common evolution of bacteria throughout our solar system, it is possible that LAL will be able to detect a microbe from Mars,鈥� says Wainwright. 鈥淲e won鈥檛 know if that鈥檚 the case until we test, but I think it is quite likely.鈥�
The irony is that while the horseshoe crab鈥檚 career in space looks set for a meteoric rise, back on Earth the ancient sea creature faces an uncertain future. On moonlit spring nights, horseshoe crabs congregate on beaches along the US eastern seaboard and engage in weird mating orgies. A female may, at times, have as many as five males latched onto her tail, all doing their best to fertilise her eggs. While distracted by sex, the crabs make easy targets. Fishermen scoop them up by the hundred as bait for catching eels and conch. Over the past decade, the numbers breeding on the New Jersey side of Delaware Bay, for example, have dropped by 90 per cent. This particular population crash has rallied support for a local protection programme but in many parts of their range, which stretches from Florida to Maine, horseshoe crabs are still intensively harvested.
鈥淭he big question in planetary protection work,鈥� says Rummel, 鈥渋s whether we can find life elsewhere without destroying it.鈥� Horseshoe crabs may someday help to answer that, but only if they can first find safety on their native beaches.