Bacteria are everywhere. We know that so-called ‘good’ bacteria swarm the inside and outside of our bodies. And with all the upcoming Christmas dinners, we are all too aware of the microbial nasties causing illnesses such as Salmonella. But really, – bacteria. aAre. eEverywhere. Scientists have previously found them existing variously at temperatures down to -20°C in Antarctic ice, and up to 115°C in the Earth’s crust. They can withstand intense pressures of up to 1000 MPa (the equivalent of 40 km beneath the Earth’s surface), and can live in both very acidic (pH 0) and very alkaline (pH 11) waters. Similarly, high concentrations of salt, andor extremely sticky viscous fluids pose no challenge to specially adapted bacteria.

A new study, carried out by researchers at Oregon State University and various other collaborators, and published this last week in a leading scientific journalUnsupported field, PLoS One, has claimed to further extend these limits with the discovery of a diverse ecosystem of bacterial life over 2 miles beneath the ocean crust.

Ocean crust, which covers around 70 percent of the Earth’s surface, is made up of three principal layers – a thin layer of sediments derived from the overlying ocean, underlain by a layer of rapidly cooled basalt that can be up to 2 miles thick. Below this is the ‘gabbro’ layer that, like the basalt layer, is derived from the mantle, but cooled more slowly. This gabbro layer makes up the bulk of the oceanic crust.

While some geological studies have been made of this layer, little work has been done to elucidate the biological activity in these rocks,. This is not only because it is difficult to get to rocks buried so deep, but also because little was thought to be going on. This new study has worked in collaboration with the Ocean Drilling Project to obtain cores of rock from the gabbro layer, which are exposed unusually close to the surface, due to uplifting and faulting at a site near the undersea mountain Atlantis Massif, in the middle of the Atlantic Ocean.

Cores of rock obtained from nearly a mile into this formation revealed a surprising and unexpected microbial habitat. A wide range of biological activity was observed in the very deep and old rocks, far away from any energy giving sunlight, and subject to intense pressures. Researchers found bacteria that were degrading hydrocarbons, and many appeared to be capable of oxidising methane.

Furthermore, the microbes seemed to be able to convert gaseous forms of nitrogen and carbon to stable solid and liquid forms.
The discovery of this busy subsurface microbial world is of interest to microbiologists, geologists and climate change scientists alike. Very little is known about the role the deep ocean crust plays in carbon storage and cycling, and such an active bacterial ecosystem in such an unpredictable place adds significantly to the limits of our knowledge. The researchers claim that the discovery can have important implications for the storage of carbon dioxide – one of the major contributing gases to the greenhouse effect and global warming. They outline the possibility of pumping carbon dioxide into the deep crust where the microbes can sequester it permanently. While the long term consequences of artificially high carbon burial in oceanic crust is not yet fully understood, the presence of this bacterial community could open up avenues of investigation into solving the climate change crisis.

This new discovery also potentially sheds light on the origin of the unexplained methane periodically observed in the atmosphere of Mars. While opinions currently differ between a geological source or a biological one, the discovery on Earth of a microbial ecosystem living deep beneath the surface of the planet (and thus out of sight of robotic explorers on Mars)opens new possibilities for subsequent exploration in seeking an explanation.

It is rare to make a truly novel discovery on Earth these days, where every conceivable area on its surface has already been explored. Now, the only places left to go are up or down, and it would now seem that down isn’t so boring after all. Who would have expected that, just as with our own bodies, bacteria would swarm the inside as well as the outside?