We analyzed the prokaryotic community structure of a saltern pond with 21% total salts located in Isla Cristina, Huelva, Southwest Spain, close to the Atlantic ocean coast. For this purpose, we constructed a metagenome (designated as IC21) obtained by pyrosequencing consisting of 486 Mb with an average read length of 397 bp and compared it with other metagenomic datasets obtained from ponds with 19, 33, and 37% total salts acquired from Santa Pola marine saltern, located in Alicante, East Spain, on the Mediterranean coast. Although the salinity in IC21 is closer to the pond with 19% total salts from Santa Pola saltern (designated as SS19), IC21 is more similar at higher taxonomic levels to the pond with 33% total salts from Santa Pola saltern (designated as SS33), since both are predominated by the phylum Euryarchaeota. However, there are significant differences at lower taxonomic levels where most sequences were related to the genus Halorubrum in IC21 and to Haloquadratum in SS33. Within the Bacteroidetes, the genus Psychroflexus is the most abundant in IC21 while Salinibacter dominates in SS33. Sequences related to bacteriorhodopsins and halorhodopsins correlate with the abundance of Haloquadratum in Santa Pola SS19 to SS33 and of Halorubrum in Isla Cristina IC21 dataset, respectively. Differences in composition might be attributed to local ecological conditions since IC21 showed a decrease in the number of sequences related to the synthesis of compatible solutes and in the utilization of phosphonate.

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.

Increasing salinization in wetland systems is a major threat to ecosystem services carried out by microbial communities. Thus, it is paramount to understand how salinity drives both microbial community structures and their diversity. Here we evaluated the structure and diversity of the prokaryotic communities from a range of highly saline soils (EC1:5 from 5.96 to 61.02 dS/m) from the Odiel Saltmarshes and determined their association with salinity and other soil physicochemical features by analyzing 16S rRNA gene amplicon data through minimum entropy decomposition (MED). We found that these soils harbored unique communities mainly composed of halophilic and halotolerant taxa from the phyla Euryarchaeota, Proteobacteria, Balneolaeota, Bacteroidetes and Rhodothermaeota. In the studied soils, several site-specific properties were correlated with community structure and individual abundances of particular sequence variants. Salinity had a secondary role in shaping prokaryotic communities in these highly saline samples since the dominant organisms residing in them were already well-adapted to a wide range of salinities. We also compared ESV-based results with OTU-clustering derived ones, showing that, in this dataset, no major differences in ecological outcomes were obtained by the employment of one or the other method.

The development of culture-independent techniques has revolutionized our understanding of microbial ecology, especially through the illustration of the vast gap between the environmentally abundant microbial diversity and that accessible through cultivation. However, culture-based approaches are not only crucial for understanding the evolutionary, metabolic and ecological milieu of microbial diversity but also for the development of novel biotechnological applications. In this study, we used a culturomics-based approach in order to isolate novel microbial taxa from hypersaline environments (i.e. Isla Cristina and Isla Bacuta salterns in Huelva, Spain). We managed to obtain axenic cultures of four haloarchaeal strains that belong to a new haloarchaeal genus and to obtain their genomic sequences. The phylogenomic and phylogenetic analyses (together with AAI, ANI and digital DDH indices) showed that the isolates constitute two new species, for which we propose the names Halosegnis longus sp. nov. and Halosegnis rubeus sp. nov. The genomic-based metabolic reconstructions indicated that members of this new haloarchaeal genus have photoheterotrophic aerobic lifestyle with a typical salt-in signature. 16S rRNA gene sequence reads abundance profiles and genomic recruitment analyses revealed that the Halosegnis genus has a worldwide geographical distribution, reaching high abundance (up to 8%) in habitats with intermediate salinities.

Four pink-pigmented, non-motile, Gram-staining-negative and moderately halophilic curved rods, designated strains SSL50 T , SSL25, SSL97 and SSL4, were isolated from a saltern located in Isla Cristina, Huelva, south-west Spain. Phylogenetic analyses based on 16S rRNA gene sequences showed that they were members of the genus Spiribacter, most closely related to Spiribacter curvatus UAH-SP71 T (99.3-99.5 % sequence similarity) and Spiribacter salinus M19-40 T (96.5-96.7 %). Other related strains were Alkalilimnicola ehrlichii MLHE-1 T (95.1-95.3 %), Arhodomonas recens RS91 T (95.1-95.2 %) and Arhodomonas aquaeolei ATCC 49307 T (95.0-95.1 %), all members of the family Ectothiorhodospiraceae. The major fatty acids were C 18 : 1 !6c and/or C 18 : 1 !7c, C 16 : 0 and C 12 : 0 . The DNA G+C range was 64.0-66.3 mol%. The DNA-DNA hybridization values between strains SSL50 T , SSL25, SSL97, SSL4 and S. piribacter. curvatus UAH-SP71 T were 37-49 %. The average nucleotide identity (ANIb) values between the genome of strain SSL50 T and those of the two other representatives of the genus Spiribacter, S. curvatus UAH-SP71 T and S. salinus M19-40 T , were 82.4 % and 79.1 %, respectively, supporting the proposal of a novel species of the genus Spiribacter. On the basis of the polyphasic analysis, the four new isolates are considered to represent a novel species of the genus Spiribacter, for which the name Spiribacter roseus sp. nov. is proposed. The type strain is SSL50 T (=CECT 9117 T =IBRC-M 11076 T ).Hypersaline environments are extreme habitats in which the main life-limiting factor is the high salt concentration. In this regard, multi-pond solar salterns constitute excellent models for studies focused on the microbial diversity and ecology over a wide range of salt concentrations. The microbial community of crystallizer ponds has been extensively studied, and their most abundant archaeal and bacterial inhabitants have been obtained in pure culture, whereas ponds with intermediate salinity have received much less attention (Ventosa et al., 1982). Moreover, studies using culture-independent techniques for the analysis of the microbial diversity dwelling in saltern ponds of intermediate salinity have shown that the most abundant microbes have not been retrieved in axenic cultures yet, possibly due to their slow growing time and particular requirement of nutrients being very different to the ones commonly used in laboratory studies (Ghai et al., 2011;Fernandez et al., 2014a, b). This has prevented the scientific community from studying and understanding the primary relationships and functions of microbes in these natural environments.Recently, León et al. (2014) described the genus Spiribacter to accommodate an abundant moderate halophile thriving in intermediate-salinity saltern ponds as ascertained by metagenomic assemblies and recruitment analysis. It belongs to the family Ectothiorhodospiraceae, within the order Chromatiales, class Gammaproteobacteria in the phylum Proteobacteria. To date, this genus includes two species is...