Microbial Roles in Caves

This Research Topic will focus on cave microorganisms and their interaction with the environment. Caves are characterized by a constant temperature, humidity, absence of light and scarcity of nutrients. A few caves shows high carbon dioxide and radon concentrations the year round. In these cases, caves have been considered as extreme environments characterized by harsh environmental conditions and low nutrient inputs where microorganisms are forced to adapt their metabolism for surviving in extreme conditions, and the low input of carbon, nitrogen and phosphorus as well as the chemical composition of the rock has a direct impact on the community diversity. The colonization of mineral substrates, speleothems, vermiculations, etc. provides complex communities active in the main biogeochemical cycles of the biosphere. Current research shows that microorganisms are involved in the formation of stalactites, moonmilk and vermiculations, as well as other mineral formations. However, the interactions of microbes with the air–water–rock interfaces in subterranean ecosystems and the biological mechanisms by which microorganisms adjust to new environments or changes in their current environment are poorly understood. In addition, caves have attracted the attention of NASA and ESA as the search for life on other Solar System bodies is a major stimulus for planetary exploration. Subterranean ecosystems (caves) are a window into hidden niches of the Earth where microorganisms adapt to live in hostile environmental conditions that could be analogues to Mars, particularly volcanic caves and extremely acidic environments (e.g. Rio Tinto in Spain). The best characterized sulfate-bearing minerals from Mars are Ca-sulfates, Mg-sulfates, jarosite and K-(Na)-Fe-(phosphate)-sulfates. Calcium- and Mg-sulfates have been observed in the interiors of some Martian meteorites, suggesting that these secondary minerals formed on Mars. Thus, cave research is useful in astrobiology as they could be good analogues for searching/identifying extraterrestrial life.

This Research Topic aims to highlight the latest information on the community structure and ecological function of cave microorganisms. Emerging tools and approaches to study cave microorganisms and their interactions with the cave environment are welcome, as well as manuscripts dealing with but not limited to the following:

• Show caves – microbial impact and interactions (lampenflora, airborne microbes, CO2, etc.).
• Biomineralization/geomicrobiology of caves: S, Fe, Mn, calcite, etc.
• Microbial roles in biogeochemical cycling in caves.
• Caves as Earth analogs for the search for extant microbial life or its remnants on extraterrestrial bodies.
• Caves as a source of new secondary metabolites from microorganisms.
• Microeukaryotic, bacterial, and archaeal diversity in caves and what factors control or influence this diversity.
• How microbial diversity varies in cave aquatic vs non-aquatic habitats.
• How does microbial diversity support macroinvertebrate/vertebrate cave diversity?
• Microbial symbioses in cave microorganisms.
• New or enhanced culture-dependent vs culture-independent methods for studying microbial diversity.
• Microbial diversity across cave types (carbonate, lava, sandstone, granite, etc.) and across substrate diversity (speleothems, guano, aquatic, etc.).