Writer: Evra Haspolat
Endoliths live inside rocks or in the pores between mineral grains found in the inner part of rocks. There are thousands of known types of endoliths, including bacteria, archaea, fungi, algae, and lichen. Endolithic microorganisms survive the extreme environmental conditions of rock pores and fissures with their survival strategies which means that they can be found in various environments, from high mountains and deep-sea floors to deserts and the Arctic and Antarctic regions. Each occupying a different climate, endoliths are classified into three main groups based on how they form living quarters in rocks. (Eren, 2019), (Sajjad et al., 2022), (Pernice et al., 2019), (Arias et al., 2023)
1- Cryptoendoliths
Cryptoendoliths are endoliths that live in rocks at the earth's surface and are thus protected from harsh environmental conditions. These microorganisms grow within structural cavities in extreme environments, such as deserts or polar regions, where external conditions like temperature, UV radiation, and moisture levels fluctuate dramatically. For example, lichen communities are the dominant form of cryptoendolith life and are found in porous rocks such as sandstone in the dry valleys of Antarctica. (Eren, 2019), (Weber & Büdel, 2011)
2- Chasmoendoliths
Chasmoendoliths inhabit natural cracks, fissures, or crevices within rocks. As they both inhabit rocks, cryptoendoliths and chasmoendoliths may be confusing. Unlike cryptoendoliths, which live deep within the rock and among mineral crystals, chasmoendoliths live in visible fractures of rock surfaces where environmental conditions may still be extreme but slightly more accessible for them than for deeper endoliths. (Weber & Büdel, 2011), (Sajjad et al., 2022), (Eren, 2019)
3- Eundoliths
Euendoliths actively bore into rocks, shells, and coral skeletons. Unlike chasmoendoliths or cryptoendoliths, which inhabit pre-existing cracks or pores, euendoliths engage in biomineralization, meaning they chemically or mechanically break down the substrate. They are generally chemolithotrophic, meaning they obtain energy from inorganic compounds. They use this energy by breaking down or changing the mineral structure of the rock. Additionally, by creating crevices, they help cryptoendoliths live in porous rocks that contain empty spaces. (Crichton, 2012), (Sajjad et al., 2022), (Weber & Büdel, 2011), (Eren, 2019)
To avoid confusion, you can refer to this table:
Endoliths’ Survival Mechanisms
Photosynthesis and pigments
Endolithic organisms such as cyanobacteria, use specialized pigments like chlorophylls to capture low-energy light that penetrates the rock surface. Even in dim light environments, they can photosynthesize effectively, making them primary producers in these ecosystems. For example, in Antarctic rocks, they thrive by using minimal light. (National Geographic Society, 2023)
Metabolic versatility
Endoliths can adapt to environments with limited nutrients by breaking down various chemicals, such as ethylbenzene and xylene, as energy sources. Their ability to break down toxins and metabolize unusual substances allows them to live in places where other life forms can’t. (Arias et al., 2023)
Biofilm Formation
Many endoliths produce protective biofilms (a structure that allows microorganisms to adhere to living or non-living surfaces and remain protected within the polymeric material they produce), UV radiation, and temperature fluctuations. Biofilms also trap moisture and nutrients, creating a micro-environment that supports survival even in extreme desert or polar conditions. (Donlan, 2022)
Endoliths’ Ecological Importance
Contribution to Biological and Geochemical Cycles
Carbon and Nitrogen Cycles
Endoliths play an important role in biochemical cycles through photosynthesis and chemosynthesis. They participate in food chains by participating in carbon and nitrogen cycles (the continuous use of carbon and nitrogen in a certain amount in the ecosystem in a cycle between living and non-living entities) and ensure the continuity of these cycles. (Okatan, 2019)
Soil Formation and Marine Ecosystems
Euendolithic organisms play a crucial role in marine ecosystems and soil formation. Similar to biofilms, xenoliths secrete acids that dissolve minerals, especially calcium carbonate, thus eroding the surface. When they are on coral reefs, these organisms erode coral skeletons and maintain the balance of marine ecosystems. On rocks, however, they erode the rock's surface and this biological process contributes to the formation of soil in the long term. (Gleason et al., 2017)
To sum up, endoliths are amazing creatures that can live in some of the harshest environments on Earth. These bacteria are crucial to ecological processes, whether found dwelling in the surface cavities of rocks, naturally occurring fissures, or actively penetrating rocks. They also contribute to soil formation, the balance of marine ecosystems, and the carbon and nitrogen cycles, highlighting the relationship between life and the environment. Their ecological roles and survival tactics demonstrate how crucial they are to preserving ecosystem health and biodiversity.
References
Arias, A. H., Hisado, V. M., Valles, P., Geyer, A., Lopez, E. G., & Cid, C. (2023, September 7). Adaptation of the Endolithic biome in Antarctic volcanic rocks. MDPI. https://www.mdpi.com/1422-0067/24/18/13824
Crichton, R. R. (2012). Biological Inorganic Chemistry. ScienceDirect. https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/biomineralization
Donlan, R. M. (2022, September). Biofilms: Microbial life on surfaces. PubMed Central (PMC). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2732559/
Eren, G. (2019, June 12). Endolitler: Kaya İçinde Yaşayan Mikroplar. Evrim Ağacı. https://evrimagaci.org/endolitler-kaya-icinde-yasayan-mikroplar-7822
Gleason, F. H., Gadd, G. M., Pitt, J. I., & Larkum, A. W. (2017, July 27). The roles of endolithic fungi in bioerosion and disease in marine ecosystems. I. General concepts. PubMed Central (PMC). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6059151/
National Geographic Society. (2023, October 31). Chlorophyll. Education | National Geographic Society. https://education.nationalgeographic.org/resource/chlorophyll/
Okatan, A. (2019, May 30). Elementlerin Doğadaki Dönüşümü | TÜBİTAK Bilim Genç. Bilim Genc. https://bilimgenc.tubitak.gov.tr/makale/elementlerin-dogadaki-donusumu
Pernice, M., Raina, J. P., Rädecker, N., Cárdenas, A., Pogoreutz, C., & Voolstra, C. R. (2019, November 5). Down to the bone: The role of overlooked endolithic microbiomes in reef coral health. OUP Academic. https://academic.oup.com/ismej/article/14/2/325/7474954?login=false
Sajjad, W., Ilahi, N., Kang, S., Bahadur, A., Zada, S., & Iqbal, A. (2022, April). Endolithic microbes of rocks, their community, function and survival strategies. ScienceDirect. https://www.sciencedirect.com/science/article/abs/pii/S0964830522000154
Weber, B., & Büdel, B. (2011). Endoliths. SpringerLink. https://link.springer.com/referenceworkentry/10.1007/978-1-4020-9212-1_80
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