Endoliths—Microbes Living within Rocks

By Monica Bruckner, Montana State University



Show description Hide This image of a rock-eating endolith was taken from a basalt found 1200 m beneath the Indian Ocean floor. Image courtesy of NOAA Ocean Explorer

What Are Endoliths?

Endoliths are organisms that live inside rocks or in pores between mineral grains. These creatures are thought to have been found in a large range of environments - from rocks on the Earth's surface to miles beneath the subsurface! There are thousands of known species of endoliths, including members from Bacteria, Archaea, and Fungi. Many endoliths are autotrophs, meaning they are able to make their own organic compounds by utilizing gas or dissolved nutrients from water moving through fractured rock. Others may incorporate inorganic compounds found in their rock substrate (possibly by excreting acids to dissolve the rock).

Where on Earth are Endoliths Found?

Endoliths have been found in a variety of environments, from the shallow surface to the deep terrestrial and ocean crust. Endoliths are a type of extremophile, which is an organism that thrives in harsh conditions. For more information about extremophiles, visit the Microbial Life Extremophile Collection.

There are several different types of endoliths, each occupying a different environment. Three major environmental groupings of endoliths are:

Cryptoendoliths - Cryptoendoliths are endoliths that live in rock on the Earth's surface. Cryptoendolithic lichen [web definition] communities are the dominant form of cryptoendolithic life and have been found in the dry valleys of Antarctica. These communities grow in porous rocks such as sandstone. Due to their tolerance for extreme conditions, cryptoendoliths have stimulated interest in exobiology, or the idea that life can exist on other planets.

Subsurface Endoliths - Subsurface endoliths can be found in groundwater aquifers or caves. These organisms do not necessarily feed on nutrients from the rock, but they may utilize nutrients found in groundwater. Some subsurface microbes may contribute to groundwater quality problems, while others may be used to remediate pollution problems. more info)

- Subsurface endoliths can be found in groundwater aquifers or caves. These organisms do not necessarily feed on nutrients from the rock, but they may utilize nutrients found in groundwater. Some subsurface microbes may contribute to groundwater quality problems, while others may be used to remediate pollution problems. Deep-Biosphere Endoliths - These endoliths have been found in deep, extremely hot (over 100 ° C) or cold (up to -15 ° C) rock, miles beneath the ocean floor. In addition, researchers have found evidence for endolithic communities surviving in deep mines, such as a South African gold mine. more info) nanobacteria collection.





What Are the Implications for Endolithic Life?

Show description Hide This photo of Bacillus infernus, a hyperthermophile, has been found 20-2800 meters beneath the Earth's surface. Photo courtesy of US Department of Energy- Subsurface Microbial Collection.

Recent work with endolithic geomicrobiology may alter our understanding of life. These microbes expand our understanding about the ability of organisms to survive and even thrive in extreme conditions. They also raise new ideas regarding the possibility of extraterrestrial life. Furthermore, these microbes may alter our ideas about the origin of life on Earth, because they have the ability to live within rock thereby escaping damaging UV rays.

Endoliths may also play a role in environmental issues. For instance, microbes living beneath the ocean floor have been suggested to play a role in the carbon cycle and global warming. Endoliths may also have environmental benefits including bioremediation of contaminated sites and mines and improvement of groundwater quality by converting harmful compounds into non-toxic waste products. In addition, these organisms may be responsible for biomineralization of economically important ores.

Show description Hide USGS researchers install diffusion samplers and microcosms to study subsurface bacteria that degrade trichloroethylene (TCE). Photo courtesy of USGS Toxics website

Deep subsurface microbes are important in our understanding the possibilities for life and have the potential for a wide range of applications that can improve the quality of life. Therefore, continued geomicrobiological research in these deep, dark environments is crucial to understanding the possibilities for life in extreme environments and for remediating environmental problems.

Endolith Collections

Additional Resources