Rocks on the surface of Mars that look like layers of pasta may be the most obvious sign of life on the Red Planet, a NASA-funded study suggests.
The bacterium that controls the formation of such rocks on Earth is ancient and thrives in harsh environments that are similar to conditions on Mars, according to the study published in the journal Astrobiology.
"It has an unusual name, Sulfurihydrogenibium yellowstonense. We just call it 'Sulfuri'," said Bruce Fouke, a professor at the University of Illinois in the US.
The bacterium belongs to a lineage that evolved prior to the oxygenation of Earth roughly 2.35 billion years ago, Fouke said.
It can survive in extremely hot, fast-flowing water bubbling up from underground hot springs.
It can withstand exposure to ultraviolet light and survives only in environments with extremely low oxygen levels, using sulphur and carbon dioxide as energy sources.
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"Taken together, these traits make it a prime candidate for colonising Mars and other planets," Fouke said.
Since it catalyses the formation of crystalline rock formations that look like layers of pasta, it would be a relatively easy life form to detect on other planets, he said.
The unique shape and structure of rocks associated with Sulfuri result from its unusual lifestyle, Fouke said.
In fast-flowing water, Sulfuri bacteria latch on to one another "and hang on for dear life," he said.
"They form tightly wound cables that wave like a flag that is fixed on one end," he said.
The waving cables keep other microbes from attaching. Sulfuri also defends itself by oozing a slippery mucus.
"These Sulfuri cables look amazingly like fettuccine pasta, while further downstream they look more like capellini pasta," Fouke said.
The researchers used sterilised pasta forks to collect their samples from Mammoth Hot Springs in Yellowstone National Park in the US.
The team analysed the microbial genomes, evaluated which genes were being actively translated into proteins and deciphered the organism's metabolic needs, Fouke said.
The team also looked at Sulfuri's rock-building capabilities, finding that proteins on the bacterial surface speed up the rate at which calcium carbonate -- also called travertine -- crystallises in and around the cables "one billion times faster than in any other natural environment on Earth," Fouke said.
The result is the deposition of broad swaths of hardened rock with an undulating, filamentous texture.
"This should be an easy form of fossilised life for a rover to detect on other planets," Fouke said.
"If we see the deposition of this kind of extensive filamentous rock on other planets, we would know it's a fingerprint of life," Fouke said.
"It's big and it's unique. No other rocks look like this. It would be definitive evidence of the presences of alien microbes," he said.