In Chile’s Atacama Desert, in a place called Laguna La Brava, scientists studied a purple ribbon of photosynthetic microbes living in a hypersaline lake that is permanently oxygen free.“I’ve been working with microbial mats for about 35 years,” says geoscientist Pieter Visscher of the University of Connecticut.“It’s the only system on Earth where I could find a microbial mat that worked absolutely in the absence of oxygen. ”
Microbial mats, which fossilize into stromatolites, have been abundant on Earth for at least 3.5 billion years, and yet, for the first billion years of their existence, there was no oxygen for the photosynthesis.
How these life forms survived under such extreme conditions is still unknown, but examining the stromatolites and extremophiles living today, researchers uncovered a handful of possibilities.
While iron, sulfur, and hydrogen have long been proposed as possible substitutes for oxygen, it was not until the discovery of “arsenotrophy” in hypersaline from Searles Lake and Mono Lake in California that arsenic has also become a competitor.
Since then, stromatolites from the Tumbiana Formation in Western Australia have revealed that trapping of light and arsenic was once a valid mode of photosynthesis in the Precambrian. The same cannot be said for iron or sulfur.
Last year, researchers discovered an abundant life form in the Pacific Ocean that also breathes arsenic.
Even La Brava’s life forms closely resemble a purple sulfur bacteria called Ectothiorhodospira sp., which was recently found in an arsenic-rich lake in Nevada that appears to photosynthesize by oxidizing the compound arsenite to a different form – arsenate.
While more research is needed to verify whether the microbes in La Brava also metabolize arsenite, initial research found that the precipitated water surrounding these mats is highly charged with hydrogen sulfide and arsenic.
If the authors are right and La Brava’s microbes “breathe” arsenic, these life forms would be the first to do so in a permanent, totally oxygen-free microbial mat, similar to what one might expect. ‘wait in Precambrian environments.
As such, his rugs are a great model for understanding some of the earliest possible life forms on our planet.
While genomic research suggests that La Brava mats have the tools to metabolize arsenic and sulfur, the authors claim that its reduction of arsenate appears to be more effective than its reduction of sulfate.
Either way, they say there is strong evidence that both pathways exist, and these would have been sufficient to support vast microbial mats in the early days of life on Earth.
If the team is correct, we may need to expand our search for life forms elsewhere.
“By looking for evidence of life on Mars, [scientists] will look at iron and probably also arsenic, ”says Visscher.
It really is more than just poison.
The study was published in Earth and environment communications.
This article was originally published by ScienceAlerte. Read the original article here.