A 'Weird' New Microorganism
30 Jul 2003
A New Form of Life
NASA Science News
July 30, 2003
NASA scientists have discovered a new extreme-loving microorganism in California's exotic Mono Lake
Mark Twain didn't think much of California's Mono Lake.
"It lies in a lifeless, treeless, hideous desert," he wrote in his 1872 travelogue, Roughing It. "This solemn, silent, sailless sea--this lonely tenant of the loneliest spot on earth--is little graced with the picturesque."
Astrobiologist Richard Hoover of NASA's National Space Science and Technology Center (NSSTC) in Huntsville, Alabama, has a different view: "It's beautiful," he says.
Mono Lake looks like an alien world. Strange knobbly spires called "tufa" jut out of the water a dozen feet in the air. The water itself is clogged with trillions of floating creatures: brine shrimp. Scoop one out and look closely. It's a miniature Alien. In the middle of the lake lies an island, covered with ash and spitting hot springs.
Mono Lake is actually a volcanic basin about 13 miles (22 km) wide. Water flows in from Sierra streams, but there's no way out again except evaporation--a process which constantly increases the concentration of salts and minerals. The "venomous waters are nearly pure lye" and twice as salty as sea water, complained Twain. "There are no fish in Mono Lake--no frogs, no snakes, no polliwogs--nothing to make life desirable."
"In fact," notes Hoover, "many things live there." The shrimp are merely one example. There's also a species of scuba-diving fly that settles mostly on the beach but sometimes swims in the water, too, navigating the lake in tiny submarine air bubbles. The lake also provides a home to microorganisms such as diatoms, cyanobacteria and filamentious algae.
So much life in such an alien place is bound to attract an astrobiologist. And in September 2000 Hoover traveled to Mono Lake to discover what else might be living there.
He was particularly interested in microbes. Many microorganisms are "extremophiles"--that is, they thrive in places that would kill bigger life forms such as fish or people. "By studying microorganisms found in Earth's extreme places, like Mono Lake, we begin to understand how life might exist on Mars or on other worlds," Hoover explains.
It was a quick visit--only one day at the lake to collect samples of water and mud, then back to the lab in Huntsville, Alabama, for analysis. But that was enough for a discovery. Deep in the lake's salty alkaline mud where no oxygen could reach, he uncovered a new species of living bacteria: Spirochaeta americana.
"These extremely thin and graceful bacteria move with an elegant motion," marvels microbiologist Elena Pikuta of the NSSTC, who cultured the samples. "Their cell walls are very delicate, and it is difficult to keep them alive for long periods in the laboratory."
The lab is probably too comfortable for anything stubborn enough to live in Mono Lake--or so Twain might say. Pikuta's rare gift for isolating and growing such microbes in a laboratory was crucial to the discovery, notes Hoover.
The genus Spirochaeta includes 13 species of bacteria. Not all of them live in harsh places like Mono Lake. Some thrive in ordinary freshwater mud--the kind kids love to play in. Most, however, love extreme environments. Spirochaeta thermophila, for instance, can be found in the high-pressure mud around deep-sea hydrothermal vents. Another example: Spirochaeta bajacaliforniensis thrives without oxygen in the sulfurous muds of Baja California. All Spirochaeta are resistant to high sulfide concentrations. Hot, salty mud stinking of sulfur seems to be a good home for these creatures.
Soon Hoover plans to return to Mono Lake to search for more microbes. It's a timely search because Mono Lake resembles a place on Mars named Gusev Crater where NASA's Mars rover Spirit will land in 2004. What will Spirit find there? Mono Lake might be giving us a preview.
There's no water in Gusev Crater today, says Hoover, but there might have been once. The crater was formed by a meteorite impact more than 3.5 billion years ago. If water was present on Mars at that time, as some researchers believe, it would have flowed into Gusev Crater through channels in a huge canyon called Ma'adim Vallis. Because the crater has no outlet, it would have become an evaporative lake site like Mono Lake.
It's unlikely that any microbes are alive in Gusev Crater now, but their fossils might be there. A good place to look would be inside evaporated mineral deposits or tufa towers, if the crater has any.
At Mono Lake microfossils are abundant in tufa. These spires are formed when calcium-rich spring water bubbles up through the lake, which is rich in bicarbonate. The calcium and bicarbonate combine, precipitating out as limestone and entombing microbes at the same time.
Tufa towers only grow while underwater, but at Mono Lake they poke above the surface. That's because the lake level has been lowered in recent years to supply water to Los Angeles, 360 miles to the south. The water level on Mars has been lowered, too. How no one knows. If Spirit spots tufa around Gusev Crater it will be a telling discovery--a clear sign of ancient water and, perhaps, an environment that once supported life.
After a week at Mono Lake, Mark Twain had had enough of the "ashes, solitude and heartbreaking silence. The cement excitement is over," he declared and gladly left.
Maybe if he had known more about Mars, and the hidden forms of life in Mono Lake, Twain would have felt differently. Astrobiologist Richard Hoover can't wait to get back.
Editors note: The discovery of Spirochaeta americana by Richard Hoover and Elena Pikuta was published in the May 2003 issue of the International Journal of Systematic and Evolutionary Microbiology. See: Spirochaeta americana sp. nov., a new haloalkaliphilic, obligately anaerobic spirochaete isolated from soda Mono Lake in California, Hoover et. al., 2003, 53, 815-821.