Os antigos micróbios comeram os cadáveres uns dos outros para sobreviver sob o mar morto

Ancient Microbes Ate Each Other's Corpses to Survive Beneath the Dead Sea

By Brandon Specktor, Senior Writer | March 26, 2019 04:46pm ET

Credit: Shutterstock

On its salty surface, the Dead Sea is famous for making giddy tourists float like beach balls. Hundreds of feet below the water, however, life is a little less fun.

Lá, sufocados por algumas das águas mais salgadas da Terra, os microrganismos unicelulares chamados archaea lutam para realizar as funções básicas da vida sem oxigênio, luz ou novas formas de sustento. De acordo com um novo estudo publicado em 22 de março na revista Geology, a sobrevivência da vida microbiana sob o Mar Morto pode ter até mesmo dependido de comer os mortos.[The 10 Strangest Places Where Life Is Found on Earth]

In their study, researchers from Switzerland and France analyzed long sediment cores drilled out of the center of the Dead Sea, and found evidence that ancient microbial life accumulated the energy it needed to survive by gobbling up bits of dead neighbors that couldn't hack the harsh conditions.

According to the researchers, these results open a window into Earth's mysterious deep biosphere — the subterranean world between Earth's surface and its core — where potentially millions of undiscovered microbial species thrive in improbably extreme conditions.

"The Dead Sea's subsurface environment constitutes one of the most extreme ecosystems on the planet," the authors wrote in their paper. "By studying an environment that pushes life to its limits, we catch a glimpse of the processes that fuel life in the deep subsurface."

Dead in the water

O Mar Morto (que não é realmente um mar, mas um lago salgado abrangendo as fronteiras de Israel, Jordânia e Palestina) começa a cerca de 1.400 pés (430 metros) abaixo do nível do mar, tornando-se o único lugar mais baixo em terra. O lago também é um dos mais salgados: suas águas são quase dez vezes mais salgadas do que os oceanos do mundo, o que dá apenas aos Archaea mais amantes do sal uma chance justa de sobrevivência.

To better understand the microbial history of this extreme ecosystem, the study authors investigated ancient sediment samples buried up to 800 feet (245 m) below the lake's surface. Inside these deep slices of lakebed, the team found traces of long-dead microbial life.

Nas camadas mais salgadas do submundo do lago, a equipe encontrou muitos compostos microbianos chamados ésteres de cera - um tipo de molécula de armazenamento de energia que os menores organismos do mundo podem criar quando sua sobrevivência é levada aos limites. Pense nisso como um minúsculo refrigerador de carbono - mas, para ativá-lo, um organismo precisa engolir alguns pedaços gordurosos deixados por micróbios mortos que não poderiam sobreviver a seus habitats agrestes.

Bacteria have been known to turn bits of their dead neighbors into wax esters before, but archaea don't seem to have this skill, the authors wrote. So, the team concluded, the wax esters found deep below the Dead Sea probably came from rough-and-tumble bacteria that had no choice but to feed on the corpses of dead archaea in order to survive their super-salty environment.

This is surprising, as bacteria were previously thought to be incapable of adapting to the lake's extreme ecosystem. However, by "recycling" bits of better-adapted microbes, that survival may have been possible in the past, the authors wrote. This may not only be true for the Dead Sea ecosystem, but could also apply to other severe environments scattered throughout the planet's vast underground biosphere.

"Our results illustrate the high adaptability of the subsurface biosphere and its ability to use varied strategies for energy production and preservation under adverse conditions," the authors concluded.

In other words, the Dead Sea might not be as dead as you thought.

• The 10 Driest Places on Earth
• The 8 Hottest Places on Earth
• Microscopic Monsters: Ugly Bugs Under the Microscope