Abstract
Incredible as it is, researchers have now the awareness that even the most extreme environment includes special habitats that host several forms of life. Cold environments cover different compartments of the cryosphere, as sea and freshwater ice, glaciers, snow, and permafrost. Although these are very particular environmental compartments in which various stressors coexist (i.e., freeze–thaw cycles, scarce water availability, irradiance conditions, and poorness of nutrients), diverse specialized microbial communities are harbored. This raises many intriguing questions, many of which are still unresolved. For instance, a challenging focus is to understand if microorganisms survive trapped frozen among ice crystals for long periods of time or if they indeed remain metabolically active. Likewise, a look at their site-specific diversity and at their putative geochemical activity is demanded, as well as at the equally interesting microbial activity at subzero temperatures. The production of special molecules such as strategy of adaptations, cryoprotectants, and ice crystal-controlling molecules is even more intriguing. This paper aims at reviewing all these aspects with the intent of providing a thorough overview of the main contributors in investigating the microbial life in the cryosphere, touching on the themes of diversity, adaptation, and metabolic potential.
Highlights
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This is the case of the Deltaproteobacteria group, mainly represented by sulphate-reducing bacteria, and of methane-generating archaeal groups identified in a brine coming from Tarn Flat, which was probably affected by anoxic conditions or upward movement of saline brine from a subsurface anoxic system, and reflected the presence of a syntrophic consortium, cycling carbon compounds in anaerobic conditions [91]
Similar conclusions were drawn by Lopatina et al [194] who detected in the snow systems surrounding two Russian Antarctic stations bacterial genera (e.g., Variovorax, Janthinobacterium, Pseudomonas, and Sphingomonas) that could be considered endogenous of Antarctica
Summary
The extreme cold environments host a great diversity of habitats and a wide variety of living organisms. The first prefer cold temperature and are more strictly related to it, while the second ones tolerate low temperatures but are able to grow until a temperature of 20 ◦C This means that their distribution is different, with psychrotrophs that are more widespread distributed, and in environments with thermal fluctuations [3,4]. The cryosphere covers about one-fifth of the surface of the Earth, with substantial seasonal variations and a long-term trend of losses in its area and volume due to climate warming. It comprises highly diversified habitats, with unique features to be considered in all studies addressed at their deeper comprehension
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