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Cyanobacterial markers in deep samples revealed by an immunoassay of Life Detector Chip. Credit: PNAS
A team of researchers from Spain, Germany and the United States has discovered a type of cyanobacterium capable of living more than 600 meters underground, in the absence of sunlight. In their article published in Proceedings of the National Academy of Sciences, the group describes their study of cyanobacteria and their discoveries.
The Spanish region of Rio Tinto has long been a substitute for Mars. The landscape is red due to the abundance of ferrous and sulphurous minerals. Because of their similarities to Mars, the researchers studied rock samples taken from above and from below, seeking to better understand what types of life can exist in such a sterile place. In this new effort, the researchers drilled a 613-meter borehole to study rock samples far from the surface. The team found cyanobacteria living in cracks and crevices in samples. Other living bacteria have been found far below the surface, but the cyanobacteria are different. Until now, scientists thought they needed sunlight to survive.
Cyanobacteria derive their energy from photosynthesis, hence the need for sunlight. They are also among the oldest forms of life on the planet. Previous research has suggested that they were responsible for adding oxygen to the atmosphere, allowing other life forms to evolve.
Viable cyanobacterial cells (red fluorescent signals) attached to rock fragments. Credit: PNAS
Surprised by their discovery, the researchers went for other samples using stricter protocols to make sure they were not contaminated. They found groups of cyanobacteria living in pockets of air in the rocks.
To find out how cyanobacteria can survive without sunlight, the team examined them under a microscope. They found that in most cases the cyanobacteria were the same as their cousins living on the surface of the surroundings. By testing the air in the pockets, they discovered that tiny creatures consumed hydrogen, as evidenced by the drop in hydrogen levels in cyanobacteria. They also found evidence that subsurface cyanobacteria had a small adaptation to their photosynthetic system that allowed them to use a "safety valve" to produce energy. In other cyanobacteria, the valve is used to release excess energy in order to avoid overheating when the sun is abundant.
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More information:
Fernando Puente-Sánchez et al. Viable cyanobacteria in deep continental subsoil, Proceedings of the National Academy of Sciences (2018). DOI: 10.1073 / pnas.1808176115
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