Three years ago, microbiologists were shocked at the discovery of life-forms in Antarctica that neither photosynthesize nor feed on others that get their energy from the Sun. Instead, these bacteria get their energy from tiny concentrations of atmospheric hydrogen. Now the same team have shown similar life forms exist in the Arctic and Tibet, expanding the conditions under which we might look for life beyond the Earth.
Most life on Earth depends on photosynthesis, using the Sun's abundant light to drive the chemical processes that draw carbon from the air and nutrients from the soil. Those of us who lack the ability feed directly or not on those that do. An exception exists around hydrothermal vents where survival depends on the heat and chemical soup that comes from the ground, possibly the original model for life.
In 2017, Dr Belinda Ferrari of the University of New South Wales reported an unexpected third form of chemosynthesis in parts of Antarctica where almost nothing else lives. “We found a weird gene that allows bacteria to take hydrogen out of the air, oxidize it, and use the energy released to feed the RuBisCo cycle,” that drives carbon fixation she told IFLScience.
Hydrogen exists as just 0.5 parts per million of the atmosphere, so it's a scarce resource to depend upon for energy. The rocky valleys where Ferrari made the discovery are also very low in water, carbon, and nitrogen, forcing the microbes to scavenge these from the air.
Scarce as atmospheric hydrogen may be, it's still more abundant than sunlight in an Antarctic winter, so it makes some sense that life-forms there would use it, rather than waiting six months to get their energy fix. The same goes in northern Canada and Norway, where Ferrari now reports in Frontiers of Microbiology she has found similar organisms.
However, the same paper describes Ferrari's detection of the same genes on the Tibetan Plateau, where it may be bitterly cold but you never have to wait long for sunlight. The drier and poorer in carbon and nitrogen a location was, the more common these genes were. Ferrari believes organisms that have gone down this path probably live throughout the world's cold deserts, and she wants to explore whether they're are present in the driest hot deserts as well.
If hydrogen consumption can allow life to survive in the coldest and driest places on Earth, perhaps this is the kind of life we should be seeking on Mars. “A future mission will take the samples back to Earth and NASA scientists will analyze the soil in a similar way we do, to try and see whether there are any indicators of life.” Ferrari said in a statement.
Ferrari told IFLScience that the organisms she has found, although sparse, almost certainly form the basis of a food chain and she wants to investigate how important they may be for the global carbon cycle.
So far, these microbes are known from their genes, having yet to be cultured. However, Ferrari noted some have been grown in the laboratory under conditions similar to their natural environment and have proven the capacity to survive on even lower concentrations of hydrogen than are typical in the atmosphere.