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Hypersaline ecosystems display taxonomically similar assemblages with low diversities and highly dense accompanying viromes. The ecological implications of viral infection on natural microbial populations remain poorly understood, especially at finer scales of diversity. Here, we sought to investigate the influence of changes in environmental physicochemical conditions and viral predation pressure by autochthonous and allochthonous viruses on host dynamics. For this purpose, we transplanted two microbiomes coming from distant hypersaline systems (solar salterns of Es Trenc in Spain and the thalassohaline lake of Aran-Bidgol lake in Iran), by exchanging the cellular fractions with the sterile-filtered accompanying brines with and without the free extracellular virus fraction. The midterm exposure (1 month) of the microbiomes to the new conditions showed that at the supraspecific taxonomic range, the assemblies from the solar saltern brine more strongly resisted the environmental changes and viral predation than that of the lake. The metagenome-assembled genomes (MAGs) analysis revealed an intraspecific transition at the ecotype level, mainly driven by changes in viral predation pressure, by both autochthonous and allochthonous viruses.

Sediments underlying the solar salterns of S'Avall are anoxic hypersaline ecosystems dominated by anaerobic prokaryotes, and with the especial relevance of putative methanogenic archaea. Slurries from salt-saturated sediments, diluted in a gradient of salinity and incubated for > 4 years revealed that salt concentration was the major selection force that deterministically structured microbial communities. The dominant archaea in the original communities showed a decrease in alpha diversity with dilution accompanied by the increase of bacterial alpha diversity, being highest at 5% salts. Correspondingly, methanogens decreased and in turn sulfate reducers increased with decreasing salt concentrations. Methanogens especially dominated at 25%. Different concentrations of litter of Posidonia oceanica seagrass added as a carbon substrate, did not promote any clear relevant effect. However, the addition of ampicillin as selection pressure exerted important effects on the assemblage probably due to the removal of competitors or enhancers. The amended antibiotic enhanced methanogenesis in the concentrations ≤ 15% of salts, whereas it was depleted at salinities ≥ 20% revealing key roles of ampicillin-sensitive bacteria.

Sebkha is an Arabic word referring to a closed ground depression temporarily occupied by a salt lake. Very few studies on the composition of the microbial communities from these ecosystems in the Algerian High Plateaus have been carried out. To fill this gap, four sebkhas in the eastern High Plateaus of two different Algerian provinces were sampled, in the winter 2020. We employed the 16S rRNA amplicon sequencing to understand the distribution and diversity of prokaryotic communities in these hypersaline soils. Our results indicate that the overall archaeal community in the hypersaline soils was dominated by members of the class Halobacteria followed by members of the yet uncultured phyla Hadarchaeota and Nanohaloarchaeota. Among the bacterial classes, Alphaproteobacteria was by far the most frequently recovered from all samples, whereas the Cyanobacteria phylum dominated in one of the sebkhas. It was evident from data that Halorubrum and Halapricum were the most abundant archaeal genera, whilst Rhodovibrio and Limimonas predominated among Bacteria, and these were present in all samples. Remarkably, the most abundant archaeal OTUs belonged to the families Haloarculaceae (16.6%) and Halobacteriaceae (16.3%).

The anaerobic hypersaline sediments of an ephemeral pond from the S’Avall solar salterns constituted an excellent study system because of their easy accessibility, as well as the analogy of their microbial assemblages with some known deep-sea hypersaline anaerobic brines. By means of shotgun metagenomics and 16S rRNA gene amplicon sequencing, the microbial composition of the sediment was shown to be stable in time and space. The communities were formed by prokaryote representatives with a clear inferred anaerobic metabolism, mainly related to the methane, sulfur and nitrate cycles. The most conspicuous finding was the inverted nature of the vertical stratification. Contrarily to what could be expected, a methanogenic archaeal metabolism was found to dominate in the upper layers, whereas Bacteria with fermentative and anaerobic respiration metabolisms increased with depth. We could demonstrate the methanogenic nature of the members of candidate lineages DHVE2 and MSBL1, which were present in high abundance in this system, and described, for the first time, viruses infecting these lineages. Members of the putatively active aerobic genera Salinibacter and Halorubrum were detected especially in the deepest layers for which we hypothesize that either oxygen could be sporadically available, or they could perform anaerobic metabolisms. We also report a novel repertoire of virus species thriving in these sediments, which had special relevance because of their lysogenic lifestyles.

The anaerobic hypersaline sediments of an ephemeral pond from the S’Avall solar salterns constituted an excellent study system because of their easy accessibility, as well as the analogy of their microbial assemblages with some known deep-sea hypersaline anaerobic brines. By means of shotgun metagenomics and 16S rRNA gene amplicon sequencing, the microbial composition of the sediment was shown to be stable in time and space. The communities were formed by prokaryote representatives with a clear inferred anaerobic metabolism, mainly related to the methane, sulfur and nitrate cycles. The most conspicuous finding was the inverted nature of the vertical stratification. Contrarily to what could be expected, a methanogenic archaeal metabolism was found to dominate in the upper layers, whereas Bacteria with fermentative and anaerobic respiration metabolisms increased with depth. We could demonstrate the methanogenic nature of the members of candidate lineages DHVE2 and MSBL1, which were present in high abundance in this system, and described, for the first time, viruses infecting these lineages. Members of the putatively active aerobic genera Salinibacter and Halorubrum were detected especially in the deepest layers for which we hypothesize that either oxygen could be sporadically available, or they could perform anaerobic metabolisms. We also report a novel repertoire of virus species thriving in these sediments, which had special relevance because of their lysogenic lifestyles.

The yeast community was studied in a municipal full-scale membrane bioreactor wastewater treatment plant (MBR-WWTP). The unexpectedly high diversity of yeasts indicated that the activated sludge formed a suitable environment for them to proliferate, with cellular concentrations of 2.2 ± 0.8 × 103 CFU ml−1 . Sixteen species of seven genera were present in the biological reactor, with Ascomycetes being the most prevalent group (93%). Most isolates were able to grow in a synthetic wastewater medium, adhere to polyethylene surfaces, and develop biofilms of variable complexity. The relationship between yeast populations and the protists in the MBR-WWTP was also studied, revealing that some protist species preyed on and ingested yeasts. These results suggest that yeast populations may play a role in the food web of a WWTP and, to some extent, contribute to membrane biofouling in MBR systems., Ministerio de Ciencia e Innovación (MICINN, España), Depto. de Genética, Fisiología y Microbiología, Fac. de Ciencias Biológicas, TRUE, pub