Chasmoendolithic

Chasmoendolithic is a term used in microbiology and geology to describe a lifestyle in which microorganisms inhabit the interior of rocks specifically along cracks and fissures (chasms) rather than within the rock pores. It is one of the main endolithic strategies, differing from cryptoendolithic, where organisms live in microscopic pore spaces, and euendolithic, which bore into the rock.

Chasmoendolithic communities are typically found in arid or extreme environments where liquid water is scarce, such as deserts, polar regions, and some caves. They are commonly reported in carbonate and silicate rocks, including limestone, sandstone, gypsum, and basalt, where crack networks provide shelter from ultraviolet radiation and temperature fluctuations.

Bacteria, including cyanobacteria, green algae, fungi, and heterotrophic bacteria, frequently compose these communities. They form biofilms along the internal surfaces of cracks and may occur as filamentous mats or thin films that trace grain boundaries and fracture planes.

Chasmoendolithic activity contributes to biogeochemical cycling and rock weathering by organic acid production and mineral alteration at the crack surfaces. As a biosignature analogue, such communities are studied for astrobiology and paleoclimate records because they can persist under harsh conditions and preserve microfabrics in rocks.

Origin of the term: from Greek chasma "gap" or "opening" + endon "within" + lithos "stone."