The hidden microbial ecosystem in the perennial ice from a Pyrenean ice cave

Bacterial diversity and geomicrobiology of Winter Wonderland ice cave, Utah, USA

The Winter Wonderland ice cave, located at an elevation of 3140 m above sea level in the Uinta Mountains of northern Utah, USA, maintains a constant sub-zero temperature. Seasonal snowmelt and rain enter the cave, freeze on the surface of the existing ice, and contribute to a 3-m-thick layered ice mass. This ice mass contains organic matter and cryogenic cave carbonates (CCCs) that date back centuries. In this study, samples of ice, liquid water, and exposed CCCs were collected to examine the bacterial communities within the cave and to determine if these communities vary spatially and between sample types. Flow cytometry showed that cell counts are an order of magnitude higher in liquid water samples than in ice. Epifluorescence microscopy and scanning electron microscopy imaging revealed potential coccoid and bacillus microbial morphologies in water samples and putative cells or calcite spherules in the CCCs. The diversity of bacteria associated with soil, identified through sequence-based analysis, supports the hypothesis that water enters the cave by filtering through soil and bedrock. A differential abundance of bacterial taxa was observed between sample types, with the greatest diversity found in CCCs. This supports a geomicrobiological framework where microbes aggregate in the water, sink into a concentrated layer, and precipitate out of the ice with the CCCs, thereby reducing the cell counts in the ice. These CCCs may provide essential nutrients for the bacteria or could themselves be products of biomineralization.

Calcium carbonate precipitating extremophilic bacteria in an Alpine ice cave

Extensive research has provided a wealth of data on prokaryotes in caves and their role in biogeochemical cycles. Ice caves in carbonate rocks, however, remain enigmatic environments with limited knowledge of their microbial taxonomic composition. In this study, bacterial and archaeal communities of the Obstans Ice Cave (Carnic Alps, Southern Austria) were analyzed by next-generation amplicon sequencing and by cultivation of bacterial strains at 10 °C and studying their metabolism. The most abundant bacterial taxa were uncultured Burkholderiaceae and Brevundimonas spp. in the drip water, Flavobacterium, Alkanindiges and Polaromonas spp. in the ice, Pseudonocardia, Blastocatella spp., uncultured Pyrinomonadaceae and Sphingomonadaceae in carbonate precipitates, and uncultured Gemmatimonadaceae and Longimicrobiaceae in clastic cave sediments. These taxa are psychrotolerant/psychrophilic and chemoorganotrophic bacteria. On a medium with Mg2+/Ca2+ = 1 at 21 °C and 10 °C, 65% and 35% of the cultivated strains precipitated carbonates, respectively. The first ~ 200 µm-size crystals appeared 2 and 6 weeks after the start of the cultivation experiments at 21 °C and 10 °C, respectively. The crystal structure of these microbially induced carbonate precipitates and their Mg-content are strongly influenced by the Mg2+/Ca2+ ratio of the culture medium. These results suggest that the high diversity of prokaryotic communities detected in cryogenic subsurface environments actively contributes to carbonate precipitation, despite living at the physical limit of the presence of liquid water.

Adaptation of the Endolithic Biome in Antarctic Volcanic Rocks

Endolithic microorganisms, ranging from microeukaryotes to bacteria and archaea, live within the cracks and crevices of rocks. Deception Island in Antarctica constitutes an extreme environment in which endoliths face environmental threats such as intense cold, lack of light in winter, high solar radiation in summer, and heat emitted as the result of volcanic eruptions. In addition, the endolithic biome is considered the harshest one on Earth, since it suffers added threats such as dryness or lack of nutrients. Even so, samples from this hostile environment, collected at various points throughout the island, hosted diverse and numerous microorganisms such as bacteria, fungi, diatoms, ciliates, flagellates and unicellular algae. These endoliths were first identified by Scanning Electron Microscopy (SEM). To understand the molecular mechanisms of adaptation of these endoliths to their environment, genomics techniques were used, and prokaryotic and eukaryotic microorganisms were identified by metabarcoding, sequencing the V3-V4 and V4-V5 regions of the 16S and 18S rRNA genes, respectively. Subsequently, the sequences were analyzed by bioinformatic methods that allow their metabolism to be deduced from the taxonomy. The results obtained concluded that some of these microorganisms have activated the biosynthesis routes of pigments such as prodigiosin or flavonoids. These adaptation studies also revealed that microorganisms defend themselves against environmental toxins by activating metabolic pathways for the degradation of compounds such as ethylbenzene, xylene and dioxins and for the biosynthesis of antioxidant molecules such as glutathione. Finally, these Antarctic endolithic microorganisms are of great interest in astrobiology since endolithic settings are environmentally analogous to the primitive Earth or the surfaces of extraterrestrial bodies.

Bacterial molecular machinery in the Martian cryosphere conditions

The exploration of Mars is one of the main objectives of space missions since the red planet is considered to be, or was in the past, potentially habitable. Although the surface of Mars is now dry and arid, abundant research suggests that water covered Mars billions of years ago. Recently, the existence of liquid water in subglacial lakes has been postulated below the South pole of Mars. Until now, experiments have been carried out on the survival of microorganisms in Martian surface conditions, but it remains unknown how their adaptation mechanisms would be in the Martian cryosphere. In this work, two bacterial species (Bacillus subtilis and Curtobacterium flacumfaciens) were subjected to a simulated Martian environment during 24 h using a planetary chamber. Afterward, the molecular machinery of both species was studied to investigate how they had been modified. Proteomes, the entire set of proteins expressed by each bacterium under Earth (named standard) conditions and Martian conditions, were compared using proteomic techniques. To establish this evaluation, both the expression levels of each protein, and the variation in their distribution within the different functional categories were considered. The results showed that these bacterial species followed a different strategy. The Bacillus subtilis resistance approach consisted of improving its stress response, membrane bioenergetics, degradation of biomolecules; and to a lesser extent, increasing its mobility and the formation of biofilms or resistance endospores. On the contrary, enduring strategy of Curtobacterium flacumfaciens comprised of strengthening the cell envelope, trying to protect cells from the extracellular environment. These results are especially important due to their implications for planetary protection, missions to Mars and sample return since contamination by microorganisms would invalidate the results of these investigations.