About this Research Topic
The deep subsurface is, in addition to space, one of the last unknown frontiers to human kind. A significant part of life on Earth resides in the deep subsurface, hiding great potential of microbial life of which we know only little. The conditions in deep terrestrial subsurface are thought to resemble those of early Earth, which makes this environment an analog for studying early life in addition to possible extraterrestrial life in ultra-extreme conditions. Furthermore, deep subsurface microorganisms offer possibilities for biotechnological applications that have yet to be discovered.
Early microorganisms played a great role in shaping the conditions on the young Earth. Even today deep subsurface microorganisms interact with their geological environment transforming the conditions in the groundwater and on rock surfaces. Essential elements for life are richly present but not necessarily in directly bioavailable form. This makes specialized metabolic strategies by microorganisms all the more important for survival and cellular maintenance in deep subsurface environments. Different energy generation strategies are continuously discussed and the use of H2 has risen to the top of the list of possible energy sources in deep subsurface. The source of the H2 is still debated. Carbon sources range from the ultimate oxidation states methane and carbonate, and the use of these demands metabolic specialization of the microorganisms. What are the nitrogen sources in deep groundwater, where typically only dissolved N2 is available?
Many of the microbial lineages detected in deep subsurface are still lacking cultured representatives, and hence very little is known about their potential functions. Nevertheless, even for the groups for which cultured representatives exist from ‘surface’ environments their functions in the subsurface may be profoundly different. How much of the genetic material of the cultured ‘surface’ species is common with the uncultured subsurface counterparts, and how much is gained/lost due to adaptation to deep geological environments?
Much new knowledge has been gained over the last decade describing the microbial communities in different terrestrial deep biospheres. The challenge now is to shed light on the activity and functional properties of the microbial communities, and to connect the biological data to that of the geological to link microbial diversity to microbial functions in the very inaccessible deep terrestrial subsurface. With this Research Topic we hope to answer some of the questions above and would like you to share your research on terrestrial deep biosphere.
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