Looking at a grain of sand under the microscope, the vile piece of silicate turns out to be the home of tens of thousands of microorganisms. To determine their spatial distribution on a grain of sand for the first time, researchers around David Probandt from the Max Planck Institute (MPI) for Marine Microbiology in Bremen colored the tiny particles with a green fluorescent marker. The result: The bacteria do not colonize their habitat evenly, but they live mainly in cracks and depressions. Not only are they protected against predators, but also against mechanical damage: "When the grains of sand are flooded with water and swirled around and rub against each other, the bacteria find a safe place in such indentations, " explains Probandt, a member of the Department of Molecular Ecology MPI.
However, the residents of 17 investigated grains of sand could not hide from the scientists of the MPI. A genetic analysis also revealed the great variety of bacteria: "On every single grain of sand we found thousands of different species." About half of all species discovered lived on each grain. Some of them live on elemental oxygen, others draw it from nitrate or sulfur oxides. It has been known for about a century that sand is a populated habitat - and how significant the unicellular organisms are for the marine ecosystem and the maintenance of global material cycles. The Sand Grain Settlers work like a filter. They pull carbon, nitrogen and other chemical compounds out of the water for their metabolism. "There is always a bacterium that processes the substances from the surrounding water, " says Probandt.
Photo: MPIMM / CC-SA BY 4.0© science.de - Jana Burczyk advertisement