The microbial life of Cerro Caliente, in Antarctica, and its similarities to Early Mars

Figure: Thermal anomaly at the top of Cerro Caliente (Antarctica), where the samples were collected for the study. © CAB

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A scientific team, led by researchers from the Centro de Astrobiología (CAB, CSIC-INTA), has studied how temperature influences microbial communities living in the geothermal area of Cerro Caliente, Isla Decepción (Antarctica). Analyses have revealed the presence of microorganisms with different thermal tolerances in all microbial communities due to strong daily temperature fluctuations, something that could have also occurred in volcanic areas on Early Mars.
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Geothermal environments in polar regions, such as Antarctica, are 'oasis' of heat and liquid water availability compared to the cold, dry environment around them. Although the temperatures that can be reached are extreme (exceed 100ºC and be below 0ºC), this combination of environments moderates temperatures on the soil surface and promotes the growth of microorganisms and plants. One of these particular areas is Cerro Caliente, on Isla Decepción.

This island is one of four active volcanoes in Antarctica, located in the South Shetland Islands, in the Bransfield Strait. This island is actually the outstanding part of the volcano and, Cerro Caliente, one of its peaks of 107 meters of altitude. Along with other areas of the island, Cerro Caliente falls within the so-called Specially Protected Antarctic Areas (ASPA). For its inaccessibility and protection, unlike other geothermal areas of the world, the microbial communities of Isla Decepción and, in particular, Cerro Caliente, have been very little characterized.

A new study, led by the Centro de Astrobiología and published in the journal Astrobiology, has characterized the microbial communities that inhabit this geothermal zone. The scientific team has studied the influence of temperature on the structure of communities and metabolisms of three microbial mats collected along the summit of Cerro Caliente. Samples recorded temperatures of 88, 8 and 2ºC at the time of collection.

Following DNA analysis of the samples, the researchers identified a varied and different composition of bacteria, archaea and eukaryotics in each. Specifically, the sample collected at 88ºC showed a higher proportion of thermophiles (organisms capable of withstanding extremely high temperatures), while in the other two samples a higher proportion of psychophiles (organisms capable of living) were found extremely low temperatures). This information, in combination with that obtained in 13C and 15N isotope analyses, allowed researchers to interpret the different metabolisms that organisms were using to extract energy from carbon and nitrogen compounds, essential for growth.

Despite these differences in composition and metabolism between samples, cyanobacteria (whose maximum temperature in some species are described around 73ºC) were identified in all mats, as well as other mesophile microorganisms (with a optimum growth temperature between 15º and 35ºC). "We think that regardless of the temperature recorded on each mat at the time of sampling, the daily thermal oscillations that occur on the surface of Cerro Caliente throughout the year may explain the presence of mesophils and others microorganisms such as cyanobacteria," explains María Angeles Lezcano, CAB researcher and lead author of the study. "The temperatures recorded in the substrate of Cerro Caliente during the year 2012 using a temperature sensor at 5cm depth, showed oscillations from 4.5º C to 76º C, with daily variations of more than 40º C. These systems are very dynamic and temperature plays an important role in determining microbial composition and metabolism," explains Lezcano.

The analogy between volcanic systems located in polar regions and early Mars, makes the geothermal zone of Cerro Caliente an ideal place for the study of biomarkers (molecules of biological origin). Despite the cold, dry conditions we know today on Mars, the presence of river valleys suggests the existence of glacio-volcanic interactions that may have melted liquid water ice. The volcanic area of Cerro Caliente thus becomes a good analogue of potentially habitable sites during the early Mars era, when similar areas may have served as a refuge for the development of microorganisms.

Considering this analogy, the scientific team used the LDChip (Life Detector Chip) to analyze samples from the three microbial mats. The LDChip is a biochip based on a catalog of antibodies generated from microorganisms that inhabit extreme places on Earth (high and low temperatures, high UV radiation, low pH, high salinity, etc.). This device is part of the SOLID (Signs Of Life Detector) instrument, developed by the CAB with the aim of being part of a future planetary exploration mission to search for remnants of life present or past on Mars. The results of The LDChip in the samples matched those of DNA in the main microbial groups. "It's a good result, and we're still working to increase the antibody catalog and optimize the instrument," concludes María Angeles Lezcano.



 

Fuente: UCC-CAB

 

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