Microbial Diversity in Moonmilk of Baeg-nyong Cave, Korean CZO

Abstract

The Baeg-nyong cave is a limestone cave which has been nominated as the first critical zone observatory (CZO) in South Korea. Moonmilk is a well-known speleothem composed of various carbonate minerals. To characterize moonmilk from the Baegnyong cave, we performed mineralogical analyses and applied high-throughput 16S rRNA gene sequencing to analyze the microbial communities, including bacteria and fungi, of dry and wet moonmilk samples. The results showed that the dry and wet moonmilk samples had different and atypical crystal structures, although they were predominantly composed of CaCO 3. Furthermore, metagenomic data revealed that the dry and wet moonmilk samples collected from an oligotrophic environment had completely different bacterial communities when compared to the outside soil, and there was a difference in bacterial communities even between dry and wet moonmilk specimens. Fungal communities, however, did not differ significantly between dry and wet moonmilk samples. This study is the first metagenomic analysis of two different types of moonmilk with different physical properties and the first report on the microbial diversity of moonmilk from a cave in the first CZO in South Korea.

Colored Microbial Coatings in Show Caves from the Galapagos Islands (Ecuador): First Microbiological Approach

“…Actinobacteria and Proteobacteria are the two most dominant phyla in caves [31,41], and a large number of actinobacterial genera were retrieved in different caves, either as isolates, clones or Next Generation Sequencing (NGS) studies. Interestingly, most of the genera and families reported in this study were also found by Gonzalez-Pimentel et al [15] and Gonzalez-Pimentel [37] in different lava tubes from La Palma Island.…”

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“…2). Fungi display a tight homeostatic control of the cytoplasmic Ca 2+ concentration as it regulates the apical growth of the hyphae and participates in several vital intracellular processes such as development and proliferation, stress response and integrity of the cell wall [50,51]. Calcium homeostasis by fungi occurs mainly in three ways: (i) the active and passive transport of Ca 2+ -ions in/out of the cell (Ca 2+ pumped ), (ii) the sequestration of cytoplasmic Ca 2+ into specific organelles (Ca 2+ organelles ) and (iii) binding to calmodulins (CaM) and calcineurins (Ca 2+ proteins ) [50].…”

“…Calcium homeostasis by fungi occurs mainly in three ways: (i) the active and passive transport of Ca 2+ -ions in/out of the cell (Ca 2+ pumped ), (ii) the sequestration of cytoplasmic Ca 2+ into specific organelles (Ca 2+ organelles ) and (iii) binding to calmodulins (CaM) and calcineurins (Ca 2+ proteins ) [50]. The pumping is performed by specific channels and antiporters fine-tune the intracellular calcium concentration [51]. Ca 2+ -ATPase are transporters capable of sequestering calcium and directing it to different organelles, such as vacuoles, Golgi and ER, decreasing cytosolic calcium levels [51].…”

“…The pumping is performed by specific channels and antiporters fine-tune the intracellular calcium concentration [51]. Ca 2+ -ATPase are transporters capable of sequestering calcium and directing it to different organelles, such as vacuoles, Golgi and ER, decreasing cytosolic calcium levels [51]. Calmodulins are cytoplasmic proteins that change their structural conformation in response to intracellular Ca 2+ levels, forming a Ca 2+ / CaM complex.…”

“…This complex becomes the binding target for several other proteins that activate specific kinases and initiate signalling cascades [52]. Calcineurins are phosphatases that activate specific transcription factors and activate signalling cascades that are involved in various biological processes [51]. On the other hand, fungal metabolic activities can increase carbonate alkalinity because of water consumption, physicochemical degassing of fungal respired CO 2 , oxidation of organic acids, nitrate assimilation or urea mineralization [45].…”