Permanent happiness without a sun protection factor
All biologists have believed in a mantra for some time: Where there is sun, there is life - where there is no sun, it will soon die. But what are man-made dogmas compared to the wonders of nature?
After a few million years of total, lightless solitude, one would think that everyone would be happy to have a spontaneous visit. Although that also depends on the circumstances. When the visit crumbles your own four walls with the brutal, all-crushing force of rotating diamond drill heads and turns everything upside down that has been dear and important to you for thousands of generations - then even we probably don't exactly say "Welcome" and offer tea. The inhabitants of a remote metabas altic fissure three kilometers below South Africa had no choice - but as typical bacteria they do not tend towards exuberant social interaction with humans anyway.
The isolated home of the germs discussed here is no longer what it was since a test well by the Anglogold Ashanti Mining Company in the ever-growing juggernaut of the Mponeng Gold Mine, the 2.825-kilometer-deep, water-bearing Crack in plutonic rock hit. Nothing spectacular for the people behind the drill pipe, that's what happens in the search for untapped ore deposits. In such cases, mine engineers get a short break and geologists like Princeton University's Li-Hung Lin get work: they take the opportunity to get at water samples and living kingdoms of organisms that haven't seen the sun in a long time.
Such investigations, even at great depths, have revealed all sorts of oddities of bacterial vegetation. Above all, however, they have always shown that sunlight is still the basis of all life, even under rocks that are kilometers deep: the bacteria that thrive in the hot water bodies of deep cracks in the rocks are dependent on a supply of substances that is slowly but unstoppably supplied by that "meteoric" water being swept downwards, originating from the natural H2O circulation at the surface and eventually percolating downwards. It carries all sorts of things with it that the plant and bacterial primary producers of the earth could ultimately only produce by photosynthesis, i.e. with the help of solar energy - and which in the end is always recycled as fuel for the tricky metabolic pathways of those life forms that live on the fringes of the earth eke out their existence in the earthly biosphere.
Chemically, these molecules are electron-donating or accepting molecules such as hydrogen or sulphate, which only have to be cleverly combined in the energy metabolism in order to stimulate a flow of electrons from A to B - and thereby generate energy to harvest. This is exactly what many of the sulfate-breathing bacteria do, for example, which Lin and other colleagues in his field have found in abundance from the depths of ocean floors or drilled rock bubbles under mine shafts. But they wouldn't exist either if the sun didn't shine far above.
Radiant from below
Lin's team wasn't particularly impressed at first when they once again found sulfate-breathing bacteria in the deep water of the Mponeng test well, which was hotter than 60 degrees and spouting out under high pressure. On closer inspection, however, the researchers discovered something that had never been seen or proven before: Apparently, the germs in the water had not had any contact with the surface for millions of years - and settled on the spot without any subcontracting work from life forms that carried out photosynthesis maintained and developed.
The water in the rock, according to the analysis of the dissolved noble gases, had not been on the surface between 3 and 25 million years. Dissolved therein, revealed the sample's C and H isotopic composition, were only carbons and hydrogens, whose signatures resembled those of Precambrian natural gases. Accordingly, they obviously originate entirely from geological, but not biological processes. However, in this ancient, purely abiotic brew, which has clearly been isolated for a long time, there was a surprisingly uniform bacterial community in which, according to genetic determinations of relationship, a single type clearly dominated - previously unknown germs of the Firmicutes group.
They are closely related to sulfate-breathing bacteria found in hydrotherms of the ocean crust. Except these relatives keep getting supplies from the surface, or they die. But where did the later generations of the Fels-Firmicutes, who were cut off from the outside world millions of years ago, obtain hydrogen and sulfate for their special respiration, at the latest after a basic stock that was perhaps initially available had been used up?
Radioactivity is the answer, suspect the scientists led by Lin, who now works at Taiwan State University. Under the mild but long-lasting radioactive bombardment from uranium, thorium or potassium-bearing ores commonly found in the pit, water occasionally decomposes into hydrogen and reactive oxygen radicals - the former serving as electron donors, the latter can then destroy local sulphurous minerals such as pyrite attack and release sulfate from it again. Incidentally, sulphate is also formed through the weathering of barite, according to Lin and Co. And with this, a self-sufficient, functioning circular economy in the rock could be maintained: The resulting SO42 + is breathed with hydrogen through the Firmicutes, which then produces sulfide again, the basis of new pyrite minerals - and so on and so forth, even over a few million years.
Out of this world
So the basis of the new community is not the sun, but the stone - more precisely, the mixture of uranium ores and sulphurous minerals that have happily combined in the 2.7 billion year old metabas alt. Lin does not speculate further at this point, imaginative researchers do. They believe this meeting to be possible, not only deep underground, but far beyond it. Maybe something similar could also take place deep in the soil of Mars or Jupiter's moon Europa and preserve life where hardly anyone thought it possible a few years ago?
Hardly discovered, the Firmicutes clan also joins the list of life forms that exobiologists like to suspect of being on foreign worlds - and even more want to search and find after they have made a little money in public relations and a lot of money in space missions. Instead of representatives like the medium-warm, but loving deep rock dwellers, their profile shows rather cold-resistant germ extremists en vogue. Neill Reid of the Space Telescope Science Institute and his colleagues have just tested one in real-life use: isolated from lakes in Antarctica, their extremely s alt-loving, methane-producing archaea representative huddled together for protection in sub-zero temperatures, surviving minus temperatures 30 degrees Celsius and was still growing happily at minus 2 degrees Celsius. Definitely suitable for Mars, says the team.
It also takes a little imagination to answer the question of where the bacteria could have come from in the snug depths or on the frosty surface of an extraterrestrial planet before they settled amidst uranium, sulphate and hydrogen or even s alt and cold at home.
Admittedly, this question hasn't really been answered satisfactorily for Earth either. Just as little as the future fate of the newly discovered Firmicutes in South Africa's depths. The culture shock triggered by the forced opening of their society initially turned out to be surprisingly negligible: Lin and co took samples from the bubbling fissure for almost sixty days – the physiochemical properties of the water and bacterial content hardly changed at all during this time, apart from the falling temperature. Unfortunately, long-term observations are out of the question: After two months, the drilling experts took over the helm again and sealed the unique habitat from scratch. Of course not out of discretion, the work had to go on.
