They thrive without oxygen, growing in salty, alkaline conditions, and may
offer insights into what kinds of life might survive on Mars. They’re a new
species of organism, isolated by scientists at the National Space Science
and Technology Center (NSSTC) in Huntsville, Ala.

The discovery, published in the May 2003 issue of the International Journal
of Systematic and Evolutionary Microbiology, identifies a species named
Spirochaeta americana by the two NSSTC scientists — Richard Hoover and Dr.
Elena Pikuta. They isolated this new organism from oxygen-deprived mud
sediments from Northern California’s Mono Lake – a salty, alkaline lake in
an enclosed volcanic basin that Hoover believes may offer new insights into
potential life on Mars.

The microorganism, a long, thin bacteria, is an extremophile — an organism
that can survive in some of the harshest conditions on Earth. Although there
are vast numbers of bacteria and archaea, only about 6,000 species have been
described and validly named and only a small fraction of them are

Like the recently discovered species, several other Spirochaeta are
extremophiles. “The environment these bacteria inhabit would be distinctly
inhospitable to many other life forms, including humans,” said Pikuta.
Humans and other multicellular organisms need oxygen to survive. Spirochaeta
americana grows in the absence of oxygen. Humans drink fresh water, while
this organism thrives in high-mineral, salty environments. On the pH, or
acidic-alkaline, scale of 0-14, humans prefer a mid-range between 6.5 and
7.5, while this organism prefers 8.0 to 10.5.

Since the first species of the genus Spirochaeta was discovered in 1835,
only 13 other species of free-living spirochetes have been found worldwide,
inhabiting environments ranging from sediments to oil fields. “These
extremely thin and graceful bacteria move with an elegant motion,” Pikuta
said. “Their cell walls are very delicate, and it is difficult to keep them
alive for long periods in the laboratory.”

The most ancient life forms on Earth, extremophiles can thrive in acid
pools, super-heated volcanic vents, glaciers, nuclear reactor wastes, at
high pressure and absolute darkness in deep-sea abysses and in rocks far
beneath the Earth’s crust — conditions that would be lethal to most other
living things.

Many also survive without oxygen. “While life requires liquid water and
energy, it doesn’t always require oxygen,” said Hoover. In fact, strictly
anaerobic microorganisms like Spirochaeta americana cannot live in the
presence of oxygen, offering encouragement to scientists who study biology
with an eye trained beyond our home planet.

“Since other bodies of the Solar System lack our oxygen-rich atmosphere,
microorganisms that thrive without oxygen are good candidates for
astrobiology research,” said Hoover. “If, or when, we find life on other
planets, our first discoveries will probably be microorganisms.”

By exploring the limits of life on Earth, these scientists hope to shed new
light on what kinds of life might exist on other places in our solar system,
such as the planet Mars or on Ganymede or Europa, two of Jupiter’s 52 moons.
Because these celestial bodies are thought to have water, scientists
consider them likely candidates to sustain life.

For this reason, microorganisms like Spirochaeta americana, that thrive in
the sulfide-rich hypersaline, alkaline mud sediments of Mono Lake are of
great interest to astrobiologists. “The goal of astrobiology is to answer
the question of whether life exists exclusively here on Earth, or is widely
distributed throughout the universe,” Hoover said.

“Planets like Mars have conditions that would challenge the existence of
highly organized multicellular organisms such as we find on Earth, but that
doesn’t mean these harsh places can’t sustain microbial life forms,” he
said. “By studying microorganisms found in Earth’s extreme places, like Mono
Lake, we can better understand how life might exist on Mars.”

Covering a 70-square-mile area, Mono Lake is a terminal lake, meaning water
does not flow through it. Instead, water enters the lake from hot alkaline
springs, rainfall and streams and leaves only by evaporation. As water
evaporates, it leaves behind chemicals that have become more concentrated
over thousands of years and many of the minerals present are formed through
microbial activity. As a result, its water is twice as salty as seawater
and extremely alkaline, with a pH of 10.

Hoover’s search for life in extreme conditions has taken him to extreme
locations, including the volcanoes of Hawaii and Greece, Antarctic mountains
and the South Pole, the permafrost of North Siberia and the glaciers of

Hoover is an astrobiologist at NASA’s Marshall Space Flight Center in
Huntsville, and Pikuta is a microbiologist with the Center for Space Plasma
and Aeronomy Research Laboratory at the University of Alabama in Huntsville.
The National Space Science and Technology Center is a partnership between
the Marshall Center, Alabama universities, industry, research institutes and
federal agencies.

— End –

The NSSTC is a cooperative venture of NASA’s Marshall Space Flight Center,
Alabama A & M University, Auburn University, Tuskegee University, The
University of Alabama, The University of Alabama at Birmingham, The
University of Alabama in Huntsville, and The University of South Alabama.