Abstract
Glaciers are populated by a large number of microorganisms including bacteria, archaea and microeukaryotes. Several factors such as solar radiation, nutrient availability and water content greatly determine the diversity and abundance of these microbial populations, the type of metabolism and the biogeochemical cycles. Three ecosystems can be differentiated in glaciers: supraglacial, subglacial and englacial ecosystems. Firstly, the supraglacial ecosystem, sunlit and oxygenated, is predominantly populated by photoautotrophic microorganisms. Secondly, the subglacial ecosystem contains a majority of chemoautotrophs that are fed on the mineral salts of the rocks and basal soil. Lastly, the englacial ecosystem is the least studied and the one that contains the smallest number of microorganisms. However, these unknown englacial microorganisms establish a food web and appear to have an active metabolism. In order to study their metabolic potentials, samples of englacial ice were taken from an Antarctic glacier. Microorganisms were analyzed by a polyphasic approach that combines a set of -omic techniques: 16S rRNA sequencing, culturomics and metaproteomics. This combination provides key information about diversity and functions of microbial populations, especially in rare habitats. Several whole essential proteins and enzymes related to metabolism and energy production, recombination and translation were found that demonstrate the existence of cellular activity at subzero temperatures. In this way it is shown that the englacial microorganisms are not quiescent, but that they maintain an active metabolism and play an important role in the glacial microbial community.
Highlights
Ice from glaciers occupies approximately 11% of the Earth’s surface[1]
It had been traditionally reported that most of the microorganisms found by sequencing were not cultivable[29,30], some researches have demonstrated that culturing samples in several culture media[24] and their subsequent functional genomic and metaproteomic analysis[31] are possible. This can allow both the identification of proteins involved in microorganism metabolism, and the identification of microorganisms that take part in biogeochemical cycles inside the glacier[24]
Culturing can increase the abundance and activity of microorganisms, enabling metaproteomic studies to model the structure of the potential microbial community
Summary
Ice from glaciers occupies approximately 11% of the Earth’s surface[1]. glaciers were traditionally considered to be an uninhabitable environment, it has been proven that they are populated by a large number of microorganisms including bacteria, archaea and microeukaryotes[2,3]. The supraglacial ecosystem is largely populated by autotrophic microorganisms exploiting the ample solar radiation and liquid water, and abundant nutrients available during ice-melt episodes[11,12,13]. Volcanic eruptions have caused the black color of glacial ice, which contains remains of lava and ash. These elements constitute an important supply of materials that are included in the ice, and form the small niches where microorganisms are housed. The main volcanic materials are basalt (rich in Mg and Ca, and in alkali oxides of Na and K) and olivine (magnesium iron silicate) All these chemical elements are abundant in the englacial ecosystem (Table 1) and can be used by microorganisms. Microscopy techniques[23] were used, subsequent attempts were made to culture[24] and isolate the microorganisms[25], while 16S and 18S rRNA sequencing techniques have more recently been used[26]
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