Bacterial diversity associated with mineral substrates and hot springs from caves and tunnels of the Naica Underground System (Chihuahua, Mexico)

Abstract

The Naica Underground System (NUS) in Northern Mexico comprises a lead, zinc, and silver producing mine and displays the largest gypsum crystals ever found in natural caves. The caves are now closed to the public and mining activities have been suspended for an undefined period since October 2015. Besides its geological, economical, and tourist importance, the bacterial diversity in the NUS has not been fully explored yet. This study surveyed for bacteria present on different mineral substrates (gypsum crystals, iron oxide crusts) and hot spring samples collected before the NUS was inaccessible, using culture-dependent and culture-independent (PCR-DGGE) methods. This study is the first reporting the isolation of microorganisms from Naica. Cluster analysis of DGGE fingerprints revealed slight differences between communities from caves and tunnels and according to their mineral substrate type while communities from solid substrates and water samples appeared to be more distant. Both approaches, culture-dependent and independent, revealed the presence of bacteria from the Firmicutes, Alphaproteobacteria, Betaproteobacteria, and Gammaproteobacteria in gypsum crystals, iron oxide crusts, and hot springs, respectively. Deinococcus-Thermus and Actinobacteria were only detected by DGGE in hot spring samples. According to 16S rRNA sequencing, heterotrophic bacteria isolated under aerobic conditions were affiliated with Bacillus, Brevibacillus, Paenibacillus, Schlegelella, Cupriavidus, Pseudoxanthomonas, and Lysobacter. Most of the isolates and sequences retrieved by DGGE were related to organisms previously detected in other extreme subsurface environments. Some of the isolates were able to precipitate calcium carbonate and precipitate Fe(III) in solid media but their possible participation in biomineralization processes in situ has still to be investigated. Microbial communities found in the NUS are likely autochthonous with some allochtonous components due to human intervention. Their role in geobiological processes requires further investigation. gypsum crystals, iron oxide crusts, hot springs, 16S rRNA, bacterial isolates, Naica

Microbial signatures from speleothems: A petrographic and scanning electron microscopy study of coralloids from the Koněprusy Caves (the Bohemian Karst, Czech Republic)

“…Most of these studies, however, have so far focused on the microbiological processes related to the origin of present-day CaCO 3 deposits, which only affect external surfaces of carbonate speleothems, or limestone cave walls and ceilings (e.g. Ercole et al, 2001;Cuezva et al, 2009;Dodge-Wan & Deng Hui Ming, 2013;Sallstedt et al, 2014;Tisato et al, 2015;Mason et al, 2016;Espina del Castillo et al, 2018).…”

Microbial ecology of tourist Paleolithic caves

“…The visitors themselves can cause strong changes in cave microclimate, with an increase in temperature, CO 2 concentrations (which can affect the chemical equilibrium of calcite) and water vapor levels (Cañveras et al, 2001;Russell and MacLean, 2008;Bastian et al, 2009b;Diaz-Herraiz et al, 2014). In Tito Bustillo and Altamira caves, water vapor exhaled by visitors resulted in condensed aerosols on cave surfaces (Cañveras et al, 2001;Espino del Castillo et al, 2018). Therefore, these visitors can also bring organic matter and dust from the outside on their shoes, or drop strands of hair and flakes of skin (Cañveras et al, 2001).…”

“…The introduction of allochthonous nutrients in tourist caves may favor the growth of heterotrophic bacteria, the development of new microbial populations, and/or the inhibition of indigenous populations (Groth et al, 1999;Bastian et al, 2009a;Bastian and Alabouvette, 2009;Espino del Castillo et al, 2018;Wasti and Seelan, 2019). The microbial diversity of anthropized and non-anthropized Paleolithic caves has been investigated for the three domains of life using new generation sequencing techniques (Alonso et al, 2019).…”

“…4). Indeed, Bacteroidetes have been proposed as bioindicators of human disturbance in tourist caves (Mulec et al, 2017;Espino del Castillo et al, 2018). Certain visited caves may even represent a reservoir of pathogens (reviewed by Saiz-Jimenez, 2012) e.g.…”

“…Certain visited caves may even represent a reservoir of pathogens (reviewed by Saiz-Jimenez, 2012) e.g. Staphylococcus and Escherichia coli (Espino del Castillo et al, 2018;Dhawi, 2020), likely linked to human inputs. Specific microbiota modifications due to anthropization may be expected at community level, with changes in species richness or community structure (Ikner et al, 2007;Ager et al, 2010;Alonso et al, 2019).…”