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New Tool Enlisted In The Search For Life On Mars

Artist's conception of ESA's ExoMars rover, which will drill 2 meters (6 feet) below the martian surface to search for signs of life. Credit: ESA - AOES Medialab
By Henry Bortman
Moffet Field CA (SPX) Mar 04, 2008
"I admit I never actually wrote this goal into my grant," UC Berkeley Professor of Chemistry Richard Mathies told me, as one of his graduate students injected a drop of Zinfandel into Mathies's organic analyzer. "But it is an important demonstration" that the detector actually works.

The device in Mathies's lab is a prototype of the Mars Organic Analyzer (MOA). Along with several other components, MOA has been selected by NASA to be part of the Urey instrument that will fly aboard ESA's ExoMars rover, scheduled for launch in 2013. Urey will be the most sophisticated life-detection instrument ever sent to Mars, and will be capable of answering questions about life on Mars that were left unanswered by NASA's Viking landers more than 30 years ago.

The MOA will take a different approach to analyzing martian soil samples than Viking did. The Viking landers had ovens that burned the soil, and instruments that sniffed at the fumes that escaped, hoping to catch a whiff of organic compounds. They didn't find any. But many researchers now believe that this test was inconclusive; even if organics were present in the soil samples, Viking's approach could have failed to detect them.

The MOA instead will use a liquid process, to look primarily for nitrogen-based compounds known as amines. The overwhelming majority of life's molecules contain amines. "Eighty to ninety percent of the dry weight of a bacterial cell is amines of various forms, mostly amino acids," says Mathies.

The first two steps prepare the sample for analysis. First, Mathies says, "you steam [the sample] with high-temperature, high-pressure water" to extract the organic material, exactly the way an espresso machine extracts coffee from ground-up beans. The second step, known as tagging, marks the amine-containing molecules for detection. The slurry from step one is mixed with a fluorescent dye. If the sample contains amines, the dye will attach itself to them.

The tagged sample is then injected into the MOA, which consists of a circular glass disk about four inches in diameter and a laser. Etched into the glass disk is a long, narrow channel, about the width of a human hair, which snakes back and forth through the interior of the disk.

When an electric field is applied to the liquid in the channel, the various compounds within it separate, positive ions going in one direction, negative ions in the other, smaller molecules moving faster than large ones. After just a couple of minutes, the contents of the sample are arrayed along the channel in predictable order.

The contents of the channel are then pushed past a tiny laser. Whenever a group of tagged molecules floats by, the light from the laser causes them to fluoresce, or give off light at a different frequency than that of the laser.

That secondary light is what the detector measures. Because different types of molecules are spread out at different points in the channel, they pass by at different times. The precise moment when a fluorescent response occurs tells Mathies the specific molecule that is present; the strength of the response tells him how much of it is there.

Here's how the wine comes into play. A few years ago, Mathies began noticing that when he had a glass or two of red wine at dinner, he'd wake up suddenly, like clockwork, at 2:30 in the morning, hot, flushed, and with an elevated heart rate and blood pressure. "It was a classic adrenaline-release, hypertensive response," he said. For a while, he simply stopped drinking wine.

Some time later he mentioned the effect to a colleague, a former neurobiologist, who said, "I know what your problem is. It's tyramine." Tyramine is a modified amino acid made within the human body, and it triggers a set of chemical reactions that ultimately cause the body to produce adrenaline. It's common in foods that are made through bacterial fermentation, such as wine, cheese and aged meats. Wouldn't it be nice, he thought, if there were some way to figure out more precisely which foods had tyramine in them, so he could stay away from them.

Then he realized he did have a way, that he'd "been working for ten years on a machine that is the most sensitive detector for organic amines you could ever imagine." He contacted winemaker Kent Rosenblum, the proprietor of Rosenblum Cellars, headquartered nearby in Alameda, Calif., and proposed a collaboration.

Using Rosenblum's 2006 pressing, he "sampled all the way through the fermentation process, to figure out when the tyramine is made," and discovered that it occurs not during primary fermentation, which is driven by yeast, but rather during a secondary fermentation process, known as malolactic fermentation, common in the production of red wine.

Malolactic fermentation converts malic acid to lactic acid. Malic acid is present in fruit; it's what makes green apples tart, but it can make wine taste sour. Lactic acid, which is present in milk, softens a wine's taste. But although malolactic fermentation may improve the taste of many wines, it also fills them with tyramines, as well as histamines, which cause allergic reactions in many people.

"Merlots seem to be particularly high," Mathies says, "but at this point we haven't done a sufficiently conclusive study" to figure out whether some varietals, or wines from specific wineries, are consistently more-tyramine-laden than others.

Long-term, Mathies hopes to see a miniaturized version of the MOA technology developed for "point-of-consumption" use. Many people have extreme sensitivities to certain foods, and can suffer severe hypertensive crises, strokes, or even death from consuming something that is, to them, toxic.

Mathies envisions a handheld PDA-like detector that a patron could use, for example, in a restaurant, to test a suspect food before eating or drinking it. Similar technology could also be used by food processors to detect harmful bacterial contamination.

Next on Mathies' agenda, however, is an ultra-clean-room test of the tabletop version of the analyzer. "The idea is to get the sensitivity to the point where the smallest quantum unit of life as we know it could be detected. The smallest living quantum unit of life is a bacterial cell."

Bacterial contamination is so pervasive on Earth that it's impossible to test this level of sensitivity without creating a special clean-room environment. "Just the handling of the solutions contaminates them so much from infall that you can't get a decent measurement," he says.

In the mean time, if you happen across a bottle of 2006 Rosenblum Zinfandel, you might want to check it out. It's not every day you get to drink a glass of wine that played a part in the search for life on Mars.

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