Chapter 35 - Taxonomical Diversity of Extremophiles in the Deep Biosphere

Abstract

In the past few years, surface drillings have expanded our perspective of the Earth’s deep biosphere from the terrestrial and oceanic realms to include deep dark subterranean and subseafloor environments. Conditions in the deep biosphere approach the limits for life, but scientific expeditions undertaken for deep subsurface life suggest that these biospheres are hosting a large fraction of microorganisms; living in water, occupying pore space, or colonizing mineral and rock surfaces. Microbes in the deep biosphere are phylogenetically different from most cultured taxa and represent novel microbial assemblages with novel metabolic capabilities. Thus, investigating these subsurface terrains, which are the deepest and potentially the largest accessible ecosystem on Earth, provides a unique opportunity for obtaining direct insights into the deep microscopic world. The insights obtained from deep biosphere expeditions are also likely to facilitate and inform exobiological exploration. This chapter describes current understanding of the subsurface depth and environmental limits of our planet’s life processes and factors that potentially define diversity/distribution of life in the deep terrestrial crustal system. The chapter also highlights the microbiological studies from the selected deep terrestrial biospheres such as hydrothermal vents, oil reservoirs, caves, and subsurface mines.