Exploring Microbial Biosignatures in Mn-Deposits of Deep Biosphere: A Preliminary Cross-Disciplinary Approach to Investigate Geomicrobiological Interactions in a Cave in Central Italy

Abstract

The terrestrial subsurface offers privileged sites both to search for microbial life and to observe still mostly unknown characteristic lithologies. In particular, caves represent natural laboratories to investigate unique minerogenetic processes and biotic interactions, connected to these phenomena. Manganese mineralization in cave environments provides a window to understand the complex Mn cycle and the development of microbial communities in special conditions, such as low constant temperature, absence of light and, in particular, low-energy environments. In the current study, we isolated and characterized Mn-samples taken from the cave “Grotta Grande dei Cervi,” L’Aquila, Central Italy, and we used a multidisciplinary approach to characterize them, with the purpose of understanding the biogeochemical processes in extreme environments. A chemical characterization of the samples was done by EDS; further investigations are underway with other multidisciplinary methodologies to understand whether the Mn laminae are related to biological processes. SEM investigations revealed microbial imprints, showing cell-like structures and suggesting that the cell-like shapes occur within internal laminae. A culture-independent approach was used to assess the possibility that biotic factors may be involved in the production of these mineralizations and to investigate the nature of the microbial community in these materials. A molecular approach was the first step to investigate the role of microorganisms in forming manganese oxides associated with water bearing rocks. DNA from the black deposits was extracted and sequence analyses of specimens were performed. Our data support the hypothesis that microorganisms may contribute to the mineralizations of manganese in this environment, providing new encouraging insight into the role of microorganisms in the Mn cycle and the processes of energy acquisition in unfavorable conditions, with relevant implications for astrobiology.

Morpho-Mineralogical and Bio-Geochemical Description of Cave Manganese Stromatolite-Like Patinas (Grotta del Cervo, Central Italy) and Hints on Their Paleohydrological-Driven Genesis

“…In this context, our microbiological data suggest that the genera identified in the samples could play a role in the Mn geochemical cycle. Moreover, our results show microbial imprints, some identified as putative predivisional cells (this fact has already been reported from other Mn deposits of Grotta del Cervo, see Vaccarelli et al, 2021), associated only with vernadite, suggesting a microbial origin for this highly disordered compound. In addition, bacteria of the genera Bacillus, Flavobacterium, Pseudomonas, Lysinibacillus, etc., appeared to be involved in calcium carbonate precipitation (Meier et al, 2017;Farrugia et al, 2019;Ortega-Villamagua et al, 2020).…”

Prokaryotic communities from a lava tube cave in La Palma Island (Spain) are involved in the biogeochemical cycle of major elements

“…The genus Hyphomicrobium and the lineage wb1-A12 were also related with manganese nodules (Molari et al, 2020). Polaromonas was found in manganese deposits from an Italian cave (Vaccarelli et al, 2021).…”

The “Infernaccio” Gorges: Microbial Diversity of Black Deposits and Isolation of Manganese-Solubilizing Bacteria

“…For each sample, the replicates were combined in an equimolar combination. Using the analytical approach previously outlined [ 6 ], we focused the analysis on the V3 and V4 regions of the 16S rRNA gene [ 18 ], using paired-end 16S rRNA gene community sequencing on the Mi-Seq Illumina platform (Bio-Fab Research, Rome, Italy). After filtering, the readings were examined for quality and counted.…”

“…The list of microorganisms implicated in Mn oxidations and reductions is continuously growing. Among the known microbes involved in transformations of Mn are conventional bacteria, such as Arthrobacter , Pseudomonas , and Bacillus , prosthecate bacteria ( Pedomicrobium , Hyphomicrobium , Metallogenium ), encapsulated bacteria (e.g., Leptothrix discophora ), and fungi ( Cephalosporium , Cladosporium , Aspergillus ) [ 6 ]. Several mechanisms have been proposed for the microbial transformation of Mn from one oxidation state to another.…”