Thanks to bacteria, there is still life in a deadly Roman cave

Maybe everything that enters this cave will die. An owl lying on the ground, and a bat too, both suffocated. Volcanic fumes seep into the cave through cracks in the ground with all their consequences. Nothing has survived at the bottom of the sulfur cave in Romania’s Mount Putoroso – nickname stinky mountain. Life also recedes outside the cave: plants begin to grow more.

Conditions are harsh due to volcanic fumes. Sulfur gas is deposited on the surface of the rock, which makes it exceptionally acidic: its pH value is 1. It is as acidic as human stomach acid, designed to break down everything that enters it. Most of life can no longer withstand a pH of 5, but here it is ten thousand times more acidic. With a protective suit you can go inside, but not for long: otherwise your shoes will melt.

Sunlight or running water will make it easier for life to settle in the cave, but this also does not exist. Since there is no sunlight, there is no energy source from which bacteria or plants can grow. And hydrocarbons do not flow like sugars, from which living organisms can draw energy.

mucous

But in 2015, researchers made an unexpected discovery. A horizontal strip about five centimeters wide extends above the cave wall, in which all kinds of microorganisms appear in a mucous substance. Together they make up a small ecosystem. An international group of scientists is now investigating this: How could an ecosystem exist there? And getting smaller, where are the limits of life?

Life in a sulfur cave is located directly on the wall where volcanic gases come into contact with “normal” air. Volcanic gas is heavier, sinks to the bottom, and there is oxygen-rich air at the top of the cave. It is easy to see where the viable strip is located, which is located on the border between volcanic gas and air: the bottom of the cave is a poisonous yellow color of precipitated sulfur.

The ecosystem could be right at the front because it uses methane from the volcanic gases at the bottom and oxygen from the air at the top, it turns out. This is thanks to one special bacterium that is the center of the micro-ecosystem, an international group of scientists wrote last week Nature Microbiology.

Bacteria are particular for many reasons. Just because they are called mycobacteria. Many mycobacteria are pathogens – the most famous of which are tuberculosis bacteria and leprosy bacteria – that do not grow without a host. “But this boy is living free,” says Wilbert Peter, professor of molecular and medical microbiology at UMC Amsterdam and VU University. “Mycobacteria have been known to grow in the environment, but there’s one that occurs prevalently in the cave, and that’s special.”

Few bacteria have mastered that

Wilbert Peter professor

Moreover, cave bacteria appear to be closely related to tuberculosis bacteria. Bitter’s company investigates many fungal bacteria, tuberculosis in particular. As a result, these bacteria teach us more about tuberculosis bacteria.

But what’s even more special is that these mycobacteria are “methanotrophic”: they can break down methane, using oxygen to do so. Bacteria can survive on the energy that is released. “It’s not that easy,” Peter says. “There are very few bacteria that have perfected that.”

The hypothesis that bacteria live this way came from Rob Van Spanning, who was searching for the energy source for the ecosystem. He is a researcher in molecular cell biology at the Free University of Amsterdam and first author of the study. “I’ve already learned about the different proteins involved in the breakdown, from methane to carbon dioxide,” he says. “So it came to me quickly, surely these bacteria can’t do that either?”

Individual steps in the process

The breakdown of methane to carbon dioxide in nature is gradual, and each step requires a different protein. With each reaction, an oxygen atom is added, or hydrogen is lost. The protein responsible for the methane reaction (CH₄) to methanol (CH .)₄s) ; Another from methanol to formaldehyde (CH₂s) ; A third is concerned with the production of formate (CHO .).₂^–); Fourth final reaction step, to CO₂.

Some known mycobacteria can perform individual steps in this process. But the mycobacteria in sulfur cave produce all four proteins, according to DNA analysis. Mycobacteria have never been found capable of doing this. Researchers suggest a logical name: Mycobacterium methane.

“We see bacteria as the basis of the food pyramid,” Spanning says. When these microorganisms die, the contents are released to other members of the community. At the top of the food pyramid there is always a predator – perhaps a cave mushroom.” Perhaps the bacteria also benefit from other bacteria, which produce nitrogenous nutrients.

“The cave shows that microorganisms have found many different solutions to live in such environments,” says Mike Gettin, professor of environmental microbiology at Radboud University Nijmegen and not associated with the research. “Nice molecular study,” says Gettin, which offers deeper insight: “The cave is almost completely closed off from the outside world. Such systems are good analogs for understanding life on ancient Earth or perhaps other planets.”