Lichtgedanken 03

S C HW E R P U N K T 37 03 | LICHT GEDANKEN The world beneath our feet is full of life, with a multitude of microorganisms constantly busy in the soils and sediments, in groundwater and even in the rocks. But life is hard underground, lacking in almost everything that organisms need in order to live: nutrients, light and energy sources. Moreover, the depths are expo- sed to extreme temperatures and high pressure. To date, very little research has been done on the microbes that brave such an inhos- pitable environment and the strategies they use to survive there. Ecologists, geoscientists and chemists from Jena are following the traces of this hidden life underground. BY UTE SCHÖNFELDER There is a saying that necessity is the mother of invention. When people lack food or other necessities of life, they are more willing to share, exchange and improvise. Things are no different in the microscopic world underground, for example in groundwater. Deep in the rocks, where rainwater accumulates after seeping through the soil, microor- ganisms cannot expect to live the high life. If they want to survive on the scar- ce supply of nutrients down below, far from the metabolic cycles above ground, they need reliable partners. Live reduced to the bare minimum »There is a whole range of microorga- nisms that have made their home in groundwater,« says Prof. Kirsten Küsel. The lives of bacteria and other single-cell organisms here are reduced to the bare minimum. »Most of these organisms have extremely reduced genomes and depend on partners for their survival,« according to the ecologist. In order to save energy, many microbes have sim- ply »shut down« or »done away with« some of their metabolic pathways and maintain only the most basic emergency programme. This helps them survive, but it means that they need metabolites from other organisms that have opted for a different energy-saving strategy, so that they can exchange substances es- sential to life. Such a precisely intercon- nected survival network makes the ecosystem in groundwater aquifers ex- tremely vulnerable, says Prof. Küsel. »If one species suffers damage or becomes extinct, its partners are also impacted.« How this subsurface microbial balance is maintained, how it arises in the first place, and what influences it, are all to- pics being investigated by researchers from Jena, together with numerous partners, as part of the Collaborative Research Centre (CRC) 1076 »AquaDi- va« (see p. 11) To this end, they have established a unique research platform in the Hainich National Park in the German state of Thuringia: the Hainich Critical Zone Ex- ploratory (CZE). In this open-air labora- tory of more than 12 square kilometres, the researchers take samples of water, gas and other materials from underg- round compartments, soils, the unsa- turated zone, and the groundwater, in order to understand their characteristics and functions. The area known as the »Critical Zone« extends from the near-surface atmo- sphere down to the bottom of ground- water aquifers. A large number of measuring and sampling sites have been set up over a six-kilometre tran- sect in the Hainich CZE. Starting in the forests of the Hainich National Park, across pasture and further on to crop- land, the researchers have drilled into the ground down to the groundwa- ter aquifers. »The boreholes go down nearly 100 metres through soil and rock layers from the quaternary period and the Upper Muschelkalk,« says Prof. Kai Uwe Totsche, hydrologist and coordina- tor of AquaDiva alongside Prof. Küsel and Prof. Susan Trumbore. In this way, the researchers were able to use the drill cores to reconstruct the soils and the geological underground of this outdoor laboratory. In addition, the water and rock samples obtained are now also providing remarkable data on the microbial communities in the sub- surface. »Astonishing« single-cell organisms »washed« from soils into the ground- water In a current publication, for example, the research team characterises the bio- diversity of what are called Archaea in groundwater and rock. These primeval single-cell organisms frequently colo- nise habitats with extreme conditions. We know of Archaea that live at tempe- ratures of over 100 degrees Celsius, for example in geysers in areas of volcanic activity. Others can withstand extremely high pressure or high salt concentrati- ons. But substantial numbers of Archaea also occur in the soil. The current Jena-based study shows that the Archaea living in the soil find their way into the groundwater when water Surviving in the subsurface Measuring tube of a groundwater well, used for va- rious purposes, such as taking groundwater samples, monitoring probes or on-site experiments.