Giant cave crystals host remarkable microbial communities

In the world’s most remarkable cave system, Naica in Mexico, cathedral-sized chambers are adorned with perfect crystals the size of trees. And scientists have now discovered that Naica hosts an astonishing array of microbial life unlike anything else on Earth.

Penelope Boston, director of the Nasa Astrobiology Institute at Ames, California, has led the exploration of this previously unknown microbial ecosystem. She outlined her findings at the American Association for the Advancement of Science conference in Boston.

Professor Boston and colleagues extracted samples from the cave surface and from water-filled inclusions within the giant gypsum crystals. They isolated and cultured an extraordinary diversity of bacteria-like organisms — about 100 types with “weird” metabolisms extracting energy from various chemical reactions including the oxidation of iron, manganese and copper sulphides.

Microbes extracted from pockets of fluid inside the crystals seemed to have been dormant for as long as 60,000 years. Viruses are present too. “What that says to me is that these are fully fledged microbial communities that have their viral load just like every other community does,” she said.

The cave is at the same time heaven and hell. “It is tear-inducingly beautiful,” Prof Boston said, “with huge crystals sparkling on orange walls.”

But the temperature is around 50C and humidity close to 100 per cent, so even wearing an ice-packed protective suit it is unsafe to remain in the cave for more than half an hour. “I once pushed it to 55 minutes and that almost did me in,” she said.

As an astrobiologist, Prof Boston believes that finding such a diversity of microbes living in extreme conditions on Earth is relevant to the search for life elsewhere in the solar system and beyond. “Any extremophile system that we study allows us to push the envelope of life further on Earth, and we add it to an atlas of possibilities that we can apply to different planetary settings,” she said.

If life does exist elsewhere in the solar system, it may well be underground, obtaining food and energy from rocks and minerals like the Naica microbes.

The Naica limestone caves in Chihuahua state were opened and drained by mining companies seeking to extract metal ores from the limestone hills. Mining operations have recently been suspended and several of the most spectacular caves are flooding again, preventing further access by scientists and others. Meanwhile Prof Boston and colleagues are preparing their microbial findings for publication in a scientific journal.