Subsurface Geomicrobiology of the Iberian Pyritic Belt

Terrestrial subsurface geomicrobiology is a matter of growing interest. On a fundamental level, it seeks to determine whether life can be sustained in the absence of radiation, whereas it also aims to develop practical applications in environmental biotechnology. Subsurface ecosystems are also intriguing exobiological models, useful for the re-creation of life on early Earth (Widdel et al. 1993) or the representation of life as it would occur in other planetary bodies (Boston et al. 1992). Subsurface ecosystems were originally reported in basalt aquifers (Stevens and McKinley 1995; Chapelle et al. 2002) and later in sedimentary aquifers, petroleum reservoirs, and alkaline and saline goldmine groundwater (Lin et al. 2006). Results obtained by deep-sea subsurface exploration initiatives are widening the scope of our knowledge in this field (D'Hondt et al. 2004). In this field there is a serious debate on whether the source of electron donors and/or acceptors is dependent on radiation-mediated reactions and also on contamination problems associated with drilling technologies, their mitigation, and control. In spite of the interest of subsurface ecosystems, information concerning microbial abundance, diversity, and sustainability is still scarce, mainly due to methodological limitations.