Abstract
Hypersaline environments encompass aquatic and terrestrial habitats. While only a limited number of studies on the microbial diversity of saline soils have been carried out, hypersaline lakes and marine salterns have been thoroughly investigated, resulting in an aquatic-biased knowledge about life in hypersaline environments. To improve our understanding of the assemblage of microbes thriving in saline soils, we assessed the phylogenetic diversity and metabolic potential of the prokaryotic community of two hypersaline soils (with electrical conductivities of ~24 and 55 dS/m) from the Odiel saltmarshes (Spain) by metagenomics. Comparative analysis of these soil databases with available datasets from salterns ponds allowed further identification of unique and shared traits of microbial communities dwelling in these habitats. Saline soils harbored a more diverse prokaryotic community and, in contrast to their aquatic counterparts, contained sequences related to both known halophiles and groups without known halophilic or halotolerant representatives, which reflects the physical heterogeneity of the soil matrix. Our results suggest that Haloquadratum and certain Balneolaeota members may preferentially thrive in aquatic or terrestrial habitats, respectively, while haloarchaea, nanohaloarchaea and Salinibacter may be similarly adapted to both environments. We reconstructed 4 draft genomes related to Bacteroidetes, Balneolaeota and Halobacteria and appraised their metabolism, osmoadaptation strategies and ecology. This study greatly improves the current understanding of saline soils microbiota.
Highlights
Extreme environments are habitats in which biodiversity is severely restrained by one or several physico-chemical factors [1]
We show that the GC content of the reads from the saline soils studied followed a bimodal the class Halobacteria (Euryarchaeota) and the bacterial genus Salinibacter, are characterized by a high distribution similar to those from salterns (Figure 1C). Most extreme halophiles, such as members genomic GC content, which has been hypothesized to help them protect against thymidine dimers of the class Halobacteria (Euryarchaeota) and the bacterial genus Salinibacter, are characterized by a high genomic GC content, which has been hypothesized to help them protect against thymidine dimers formation caused by the high solar radiation that most hypersaline environments are subjected to [67,69,70]
Bacterial diversity is higher than in aquatic ecosystems and some groups without known halophilic representatives are present in soils, albeit in low proportions, which suggests that the specific properties of terrestrial and aquatic habitats may be key in determining the presence and abundance of highly specialized microorganisms and those others variably adapted to salinity
Summary
Extreme environments are habitats in which biodiversity is severely restrained by one or several physico-chemical factors [1]. The harshness of hypersaline environments is often increased by concurrent low concentrations of dissolved oxygen and nutrients, extreme pH values and high temperatures, pressures, and the presence of toxic compounds. These environments include saline lakes, marine salterns, salted foods, deep-sea brine pools and saline soils and sediments [2]. Recent research into the prokaryotic diversity and ecology of aquatic hypersaline environments addressed by shotgun metagenomics revealed a change in biodiversity, abundance of specific taxa and osmoadaptation mechanisms along a salinity gradient [22,23,24,25], uncovered the presence of new phylogenetic groups [22,25,26] and even fostered the isolation of previously untapped taxa in pure culture [27]. The integration of our results with those from extensively studied aquatic systems and the limited available biodiversity studies on saline soils has allowed to evaluate the biases of the current knowledge about halophiles and their ecology
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