A glimpse of the prokaryotic diversity of the Large Aral Sea reveals novel extremophilic bacterial and archaeal groups

SALINITY-Induced Changes in Diversity, Stability, and Functional Profiles of Microbial Communities in Different Saline Lakes in Arid Areas

Saline lakes, characterized by high salinity and limited nutrient availability, provide an ideal environment for studying extreme halophiles and their biogeochemical processes. The present study examined prokaryotic microbial communities and their ecological functions in lentic sediments (with the salinity gradient and time series) using 16S rRNA amplicon sequencing and a metagenomic approach. Our findings revealed a negative correlation between microbial diversity and salinity. The notable predominance of Archaea in high-salinity lakes signified a considerable alteration in the composition of the microbial community. The results indicate that elevated salinity promotes homogeneous selection pressures, causing substantial alterations in microbial diversity and community structure, and simultaneously hindering interactions among microorganisms. This results in a notable decrease in the complexity of microbial ecological networks, ultimately influencing the overall ecological functional responses of microbial communities such as carbon fixation, sulfur, and nitrogen metabolism. Overall, our findings reveal salinity drives a notable predominance of Archaea, selects for species adapted to extreme conditions, and decreases microbial community complexity within saline lake ecosystems.

Unveiling the microbial diversity across the northern Ninety East Ridge in the Indian Ocean

Prokaryotes play a crucial role in marine ecosystem health and drive biogeochemical processes. The northern Ninety East Ridge (NER) of the Indian Ocean, a pivotal yet understudied area for these cycles, has been the focus of our study. We employed high-throughput 16S rRNA gene sequencing to analyze 35 water samples from five stations along the ridge, categorized into three depth- and dissolved oxygen-level-based groups. Our approach uncovered a clear stratification of microbial communities, with key bioindicators such as Prochlorococcus MIT9313, Sva0996 marine group, and Candidatus Actinomarina in the upper layer; Ketobacter, Pseudophaeobacter, Nitrospina, and SAR324 clade in the middle layer; and Methylobacterium-Methylorubrum, Sphingomonas, Sphingobium, and Erythrobacter in the deep layer. Methylobacterium-Methylorubrum emerged as the most abundant bacterial genus, while Nitrosopumilaceae predominated among archaeal communities. The spatial and depth-wise distribution patterns revealed that Ketobacter was unique to the northern NER, whereas Methylobacterium-Methylorubrum, UBA10353, SAR324 clade, SAR406, Sva0996_marine_group, Candidatus Actinomarina were ubiquitous across various marine regions, exhibiting niche differentiation at the OTU level. Environmental factors, especially dissolved oxygen (DO), silicate, nitrate, and salinity, significantly influence community structure. These findings not only reveal the novelty and adaptability of the microbial ecosystem in the northern NER but also contribute to the broader understanding of marine microbial diversity and its response to environmental heterogeneity.

Novel insights into the diversity of halophilic microorganisms and their functioning in hypersaline ecosystems

Our understanding of the microbial diversity inhabiting hypersaline environments, here defined as containing >100-150 g/L salts, has greatly increased in the past five years. Halophiles are found in each of the three domains of life. Many novel types have been cultivated, and metagenomics and other cultivation-independent approaches have revealed the existence of many previously unrecognized lineages. Syntrophic interactions between different phylogenetic lineages have been discovered, such as the symbiosis between members of the archaeal class Halobacteria and the 'Candidatus Nanohalarchaeota'. Metagenomics techniques also have shed light on the biogeography of halophiles, especially of the genera Salinibacter (Bacteria) and Haloquadratum and Halorubrum (Archaea). Exploration of the microbiome of hypersaline lakes led to the discovery of novel types of metabolism previously unknown to occur at high salt concentrations. Studies of environments with high concentrations of chaotropic ions such as magnesium, calcium, and lithium have refined our understanding of the limits of life.

Viral Community Structure and Potential Functions in the Dried-Out Aral Sea Basin Change along a Desiccation Gradient

The dried-out Aral Sea basin represents an extreme environment due to a man-made ecological disaster. Studies conducted in this unique environment revealed high levels of pollution and a specifically adapted microbiota; however, viral populations remained entirely unexplored. By employing an in-depth analysis based on the sequencing of metagenomic DNA recovered from rhizosphere samples of Suaeda acuminata (C. A. Mey.) Moq. along a desiccation gradient of 5, 10, and 40 years, we detected a diverse viral community comprising 674 viral populations (viral operational taxonomic units [vOTUs]) dominated by Caudovirales. Targeted analyses highlighted that viral populations in this habitat are subjected to certain dynamics that are driven mainly by the gradient of desiccation, the corresponding salinity, and the rhizosphere bacterial populations. In silico predictions linked the viruses to dominant prokaryotic taxa in the Aral Sea basin, such as Gammaproteobacteria, Actinomycetia, and Bacilli. The lysogenic lifestyle was predicted to be predominant in areas that dried out 5 years ago, representing the early revegetation phase. Metabolic prediction of viral auxiliary metabolic genes (AMGs) suggests that viruses may play a role in the biogeochemical cycles, stress resilience, and competitiveness of their hosts due to the presence of genes that are involved in biofilm formation. Overall, our study provides important insights into viral ecology in an extreme environment and expands our knowledge related to virus occurrence in terrestrial systems. IMPORTANCE Environmental viruses have added a wealth of knowledge to ecological studies with the emergence of metagenomic technology and approaches. They are also becoming recognized as important genetic repositories that underpin the functioning of terrestrial ecosystems but have remain moslty unexplored. Using shotgun metagenome sequencing and bioinformatic tools, we found that the viral community structure was affected during natural revegetation in the dried-up Aral Sea area, a model habitat for investigating natural ecological restoration but still understudied. In this study, we highlight the importance of viruses, elements that are overlooked, for their potential contribution to terrestrial ecosystems, i.e., nutrient cycles, stress resilience, and host competitiveness, during natural revegetation.

Function-Based Rhizosphere Assembly along a Gradient of Desiccation in the Former Aral Sea

The desiccation of the Aral Sea represents one of the largest human-made environmental regional disasters. The salt- and toxin-enriched dried-out basin provides a natural laboratory for studying ecosystem functioning and rhizosphere assembly under extreme anthropogenic conditions. Here, we investigated the prokaryotic rhizosphere communities of the native pioneer plant Suaeda acuminata (C.A.Mey.) Moq. in comparison to bulk soil across a gradient of desiccation (5, 10, and 40 years) by metagenome and amplicon sequencing combined with quantitative PCR (qPCR) analyses. The rhizosphere effect was evident due to significantly higher bacterial abundances but less diversity in the rhizosphere compared to bulk soil. Interestingly, in the highest salinity (5 years of desiccation), rhizosphere functions were mainly provided by archaeal communities. Along the desiccation gradient, we observed a significant change in the rhizosphere microbiota, which was reflected by (i) a decreasing archaeon-bacterium ratio, (ii) replacement of halophilic archaea by specific plant-associated bacteria, i.e., Alphaproteobacteria and Actinobacteria, and (iii) an adaptation of specific, potentially plant-beneficial biosynthetic pathways. In general, both bacteria and archaea were found to be involved in carbon cycling and fixation, as well as methane and nitrogen metabolism. Analysis of metagenome-assembled genomes (MAGs) showed specific signatures for production of osmoprotectants, assimilatory nitrate reduction, and transport system induction. Our results provide evidence that rhizosphere assembly by cofiltering specific taxa with distinct traits is a mechanism which allows plants to thrive under extreme conditions. Overall, our findings highlight a function-based rhizosphere assembly, the importance of plant-microbe interactions in salinated soils, and their exploitation potential for ecosystem restoration approaches. IMPORTANCE The desertification of the Aral Sea basin in Uzbekistan and Kazakhstan represents one of the most serious anthropogenic environmental disasters of the last century. Since the 1960s, the world's fourth-largest inland body of water has been constantly shrinking, which has resulted in an extreme increase of salinity accompanied by accumulation of many hazardous and carcinogenic substances, as well as heavy metals, in the dried-out basin. Here, we investigated bacterial and archaeal communities in the rhizosphere of pioneer plants by combining classic molecular methods with amplicon sequencing as well as metagenomics for functional insights. By implementing a desiccation gradient, we observed (i) remarkable differences in the archaeon-bacterium ratio of plant rhizosphere samples, (ii) replacement of archaeal indicator taxa during succession, and (iii) the presence of specific, potentially plant-beneficial biosynthetic pathways in archaea present during the early stages. In addition, our results provide hitherto-undescribed insights into the functional redundancy between plant-associated archaea and bacteria.

Could Pontimonas Harbour Halophilic Members Able to Withstand Very Broad Salinity Variations?

Pontimonas is currently described as a genus including only one species of slightly halophilic marine bacteria. Although some works revealed its presence in some hypersaline environments, the information on its habitat preference is still scant. This work investigated Pontimonas presence in selected ponds of the Saline di Tarquinia marine saltern and in the seawater intake area. The two-year metabarcoding survey documented its constant presence along the ponds establishing the salinity gradient and in a distinct basin with permanent hypersaline conditions (BSB). Pontimonas was higher in the ponds than in the sea, whereas it had similar abundances in the sea and in the BSB. Its representative OTUs showed significant trends according to different parameters. Along the salinity gradient, OTU1 abundance increased with decreasing water temperatures and increasing rainfalls, and it showed a maximum in January; OTU2 increased with increasing BOD5 and it showed the highest abundances in the period August–October, and OTU 3194 increased at decreasing salinities. In BSB, a significant seasonal variation was shown by OTU 3194, which started increasing in spring to reach a maximum in summer. The results suggest that Pontimonas could easily settle in hypersaline habitats, having also broad euryhaline members and some possible extreme halophilic representatives.

The Methods of Digging for "Gold" within the Salt: Characterization of Halophilic Prokaryotes and Identification of Their Valuable Biological Products Using Sequencing and Genome Mining Tools

Halophiles, the salt-loving organisms, have been investigated for at least a hundred years. They are found in all three domains of life, namely Archaea, Bacteria, and Eukarya, and occur in saline and hypersaline environments worldwide. They are already a valuable source of various biomolecules for biotechnological, pharmaceutical, cosmetological and industrial applications. In the present era of multidrug-resistant bacteria, cancer expansion, and extreme environmental pollution, the demand for new, effective compounds is higher and more urgent than ever before. Thus, the unique metabolism of halophilic microorganisms, their low nutritional requirements and their ability to adapt to harsh conditions (high salinity, high pressure and UV radiation, low oxygen concentration, hydrophobic conditions, extreme temperatures and pH, toxic compounds and heavy metals) make them promising candidates as a fruitful source of bioactive compounds. The main aim of this review is to highlight the nucleic acid sequencing experimental strategies used in halophile studies in concert with the presentation of recent examples of bioproducts and functions discovered in silico in the halophile's genomes. We point out methodological gaps and solutions based on in silico methods that are helpful in the identification of valuable bioproducts synthesized by halophiles. We also show the potential of an increasing number of publicly available genomic and metagenomic data for halophilic organisms that can be analysed to identify such new bioproducts and their producers.

Thermococcus bergensis sp. nov., a Novel Hyperthermophilic Starch-Degrading Archaeon

Simple Summary

Hyperthermophiles grow optimally above 80 °C and include mostly microorganisms belonging to the Archaea domain and are thriving in terrestrial and seafloor geothermal vents as well as in subsurface environments. From an anaerobic hyperthermophilic mixed culture obtained from water produced from a deep and hot oil reservoir we isolated and characterized a starch-degrading strain. Based on phylogenomic analysis, the strain represents a novel hyper-thermophilic species belonging to genus Thermococcus, for which we propose the name Thermococcus bergensis sp. nov.

Abstract

A novel hyperthermophilic archaeon, termed strain T7324^T, was isolated from a mixed sulfate-reducing consortium recovered from hot water produced from a deep North Sea oil reservoir. The isolate is a strict anaerobic chemo-organotroph able to utilize yeast extract or starch as a carbon source. The genes for a number of sugar degradation enzymes and glutamate dehydrogenase previously attributed to the sulfate reducing strain of the consortium (Archaeoglobus fulgidus strain 7324) were identified in the nearly completed genome sequence. Sequence analysis of the 16S rRNA gene placed the strain in the Thermococcus genus, but with an average nucleotide identity that is less than 90% to its closest relatives. Phylogenomic treeing reconstructions placed the strain on a distinct lineage clearly separated from other Thermococcus spp. The results indicate that the strain T7324^T represents a novel species, for which the name Thermococcus bergensis sp. nov. is proposed. The type strain is T7324^T (=DSM 27149^T = KCTC 15808^T).

Onshore soil microbes and endophytes respond differently to geochemical and mineralogical changes in the Aral Sea

There is limited knowledge about how microbiome develops along the geochemical and mineralogical change in onshore soils derived from continuous desiccation of lakes. In this study, geochemistry and mineralogy were studied in the Aral Sea onshore soils exposed in different periods (from the 1970s to 2018), followed by microbial analyses on the studied soils and the aboveground organs of dominant plants. The soils exhibited an increasing gradient of total soluble salts (TSS: 0.4-0.5 g/L to 71.3 g/L) and evaporite minerals (e.g., gypsum, halite) from the farshore to the nearshore. In the studied soils, microbial diversity decreased with increasing TSS, and microbial community dissimilarities among samples was positively correlated with the contents of gypsum and calcite minerals. Among the measured environmental variables, minerals contributed most to the observed microbial variation. In contrast, the endophytic microbial communities in the aboveground organs of dominant plants were not related to any of the measured variables, indicating that they differed from their soil counterparts with respect to their responses to geochemical and mineralogical variations in soils. In summary, these results help us understand the response of onshore soil microbiome to the decline of lake water caused by continuous desiccation.

Spatio-Temporal Variation of the Bacterial Communities along a Salinity Gradient within a Thalassohaline Environment (Saline di Tarquinia Salterns, Italy)

The “Saline di Tarquinia” salterns have been scarcely investigated regarding their microbiological aspects. This work studied the structure and composition of their bacterial communities along the salinity gradient (from the nearby sea through different ponds). The communities showed increasing simplification of pond bacterial diversity along the gradient (particularly if compared to those of the sea). Among the 38 assigned phyla, the most represented were Proteobacteria, Actinobacteria and Bacteroidetes. Differently to other marine salterns, where at the highest salinities Bacteroidetes dominated, preponderance of Proteobacteria was observed. At the genus level the most abundant taxa were Pontimonas, Marivita, Spiribacter, Bordetella, GpVII and Lentibacter. The α-diversity analysis showed that the communities were highly uneven, and the Canonical Correspondence Analysis indicated that they were structured by various factors (sampling site, sampling year, salinity, and sampling month). Moreover, the taxa abundance variation in relation to these significant parameters were investigated by Generalized Linear Models. This work represents the first investigation of a marine saltern, carried out by a metabarcoding approach, which permitted a broad vision of the bacterial diversity, covering both a wide temporal span (two years with monthly sampling) and the entire salinity gradient (from the nearby sea up to the crystallisation ponds).

Epipelagic microbiome of the Small Aral Sea: Metagenomic structure and ecological diversity

Microbial diversity studies regarding the aquatic communities that experienced or are experiencing environmental problems are essential for the comprehension of the remediation dynamics. In this pilot study, we present data on the phylogenetic and ecological structure of microorganisms from epipelagic water samples collected in the Small Aral Sea (SAS). The raw data were generated by massive parallel sequencing using the shotgun approach. As expected, most of the identified DNA sequences belonged to Terrabacteria and Actinobacteria (40% and 37% of the total reads, respectively). The occurrence of Deinococcus-Thermus, Armatimonadetes, Chloroflexi in the epipelagic SAS waters was less anticipated. Surprising was also the detection of sequences, which are characteristic for strict anaerobes-Ignavibacteria, hydrogen-oxidizing bacteria, and archaeal methanogenic species. We suppose that the observed very broad range of phylogenetic and ecological features displayed by the SAS reads demonstrates a more intensive mixing of water masses originating from diverse ecological niches of the Aral-Syr Darya River basin than presumed before.

Draft Genome Sequence of Escherichia coli Strain Tj, Isolated from the Varzob River in Tajikistan

The 4.6-Mbp draft genome sequence of Escherichia coli strain Tj, isolated from the Varzob River in Tajikistan, is presented. This strain possesses four prophage elements related to Shigella phage SfV, E. coli O157:H7-specific phage ϕV10, lambdoid phage HK225, and coliphage Ayreon. It contains a gene encoding a hemolysin E toxin.

A glimpse of the prokaryotic diversity of the Large Aral Sea reveals novel extremophilic bacterial and archaeal groups

During the last five decades, the Aral Sea has gradually changed from a saline water body to a hypersaline lake. Microbial community inhabiting the Aral Sea has been through a succession and continuous adaptation during the last 50 years of increasing salinization, but so far, the microbial diversity has not been explored. Prokaryotic diversity of the Large Aral Sea using cultivation‐independent methods based on determination of environmental 16S rRNA gene sequences revealed a microbial community related to typical marine or (hyper) saline‐adapted Bacteria and Archaea. The archaeal sequences were phylogenetically affiliated with the order Halobacteriales, with a large number of operational taxonomic units constituting a novel cluster in the Haloferacaceae family. Bacterial community analysis indicated a higher diversity with representatives belonging to Proteobacteria, Actinobacteria and Bacteroidetes. Many members of Alphaproteobacteria and Gammaproteobacteria were affiliated with genera like Roseovarius, Idiomarina and Spiribacter which have previously been found in marine or hypersaline waters. The majority of the phylotypes was most closely related to uncultivated organisms and shared less than 97% identity with their closest match in GenBank, indicating a unique community structure in the Large Aral Sea with mostly novel species or genera.