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PubMed2004

Evolution of the RNA polymerase B' subunit gene (rpoB') in Halobacteriales: a complementary molecular marker to the SSU rRNA gene.

Many prokaryotes have multiple ribosomal RNA operons. Generally, sequence differences between small subunit (SSU) rRNA genes are minor (<1%) and cause little concern for phylogenetic inference or environmental diversity studies. For Halobacteriales, an order of extremely halophilic, aerobic Archaea, within-genome SSU rRNA sequence divergence can exceed 5%, rendering phylogenetic assignment problematic. The RNA polymerase B' subunit gene (rpoB') is a single-copy conserved gene that may be an appropriate alternative phylogenetic marker for Halobacteriales. We sequenced a fragment of the rpoB' gene from 21 species, encompassing 15 genera of Halobacteriales. To examine the utility of rpoB' as a phylogenetic marker in Halobacteriales, we investigated three properties of rpoB' trees: the variation in resolution between trees inferred from the rpoB' DNA and RpoB' protein alignment, the degree of mutational saturation between taxa, and congruence with the SSU rRNA tree. The rpoB' DNA and protein trees were for the most part congruent and consistently recovered two well-supported monophyletic groups, the clade I and clade II haloarchaea, within a collection of less well resolved Halobacteriales lineages. A comparison of observed versus inferred numbers of substitution revealed mutational saturation in the rpoB' DNA data set, particularly between more distant species. Thus, the RpoB' protein sequence may be more reliable than the rpoB' DNA sequence for inferring Halobacteriales phylogeny. AU tests of tree selection indicated the trees inferred from rpoB' DNA and protein alignments were significantly incongruent with the SSU rRNA tree. We discuss possible explanations for this incongruence, including tree reconstruction artifact, differential paralog sampling, and lateral gene transfer. This is the first study of Halobacteriales evolution based on a marker other than the SSU rRNA gene. In addition, we present a valuable phylogenetic framework encompassing a broad diversity of Halobacteriales, in which novel sequences can be inserted for evolutionary, ecological, or taxonomic investigations.

Base Sequence↗

PubMed2006

Phylogenetic relationships within the order Halobacteriales inferred from 16S rRNA gene sequences.

Phylogenetic relationships within the halophilic archaea were inferred from comparisons of the 16S rRNA gene sequences from 61 strains, representing 18 genera with validly published names within the order Halobacteriales. Trees produced using distance-matrix (least-squares and neighbour-joining) methods affirm with strong bootstrap support that the members of the order Halobacteriales are a monophyletic group. Ten genera were supported as monophyletic groups [Haloarcula, Halobiforma, Halococcus, Haloferax, Halorubrum, Halosimplex (multiple sequences from a single strain), Natrialba, Natrinema, Natronococcus and Natronorubrum] and eight genera were represented by a single strain (Halobacterium, Halobaculum, Halogeometricum, Halomicrobium, Halorhabdus, Halosimplex, Natronobacterium and Natronomonas). The genus Haloterrigena was always paraphyletic, and the phylogenetic placement of and sister groups to Halobacterium and Natronomonas could not be resolved. Both treeing methods failed to resolve the deep branching patterns within the order Halobacteriales and the relationships between the major clades. Additional representation from the currently monospecific genera and/or the use of other macromolecules may be required to resolve the relationships within the order Halobacteriales.

Base Sequence↗

PubMed2005

The nomenclatural types of the orders Acholeplasmatales, Halanaerobiales, Halobacteriales, Methanobacteriales, Methanococcales, Methanomicrobiales, Planctomycetales, Prochlorales, Sulfolobales, Thermococcales, Thermoproteales and Verrucomicrobiales are the genera Acholeplasma, Halanaerobium, Halobacterium, Methanobacterium, Methanococcus, Methanomicrobium, Planctomyces, Prochloron, Sulfolobus, Thermococcus, Thermoproteus and Verrucomicrobium, respectively. Opinion 79.

The Judicial Commission of the International Committee on Systematics of Prokaryotes has corrected the nomenclatural types of 12 orders: Acholeplasmatales, Halanaerobiales, Halobacteriales, Methanobacteriales, Methanococcales, Methanomicrobiales, Planctomycetales, Prochlorales, Sulfolobales, Thermococcales, Thermoproteales and Verrucomicrobiales.

Archaea↗

PubMed2026

Halolitoreus marinus gen. nov., sp. nov. and Halolitoreus rarus sp. nov., halophilic archaea isolated from diverse coastal tidal flats, and proposal of the novel family Halolitoreaceae fam. nov. in the order Halobacteriales within the class Halobacteria.

Coastal tidal flats represent dynamic saline environments that harbor largely unexplored haloarchaeal communities. In this study, amplicon sequencing, metagenomic analyses, and cultivation-based approaches revealed substantial haloarchaeal diversity in tidal flats from four provinces of eastern China despite their relatively low salinity. Five haloarchaeal strains, designated YSMS36T, DYSN1, QDMS2, CMSO5T, and ZSTT2, were isolated from diverse tidal flats. Theses strains shared 16S rRNA gene sequence similarities of 92.1-92.2% with their closest validly named relative, Salinilacihabitans rarus AD-4T. Phylogenetic analyses based on 16S rRNA and rpoB' gene sequences showed that the five strains formed a distinct and well-supported monophyletic lineage, separated from currently recognized members of the class Halobacteria. Average amino acid identity (AAI), average nucleotide identity (ANI), and digital DNA-DNA hybridization (dDDH) values between these five strains and the related Halobacteria representatives were 49.3-62.7%, 66.9-74.9%, and 16.2-29.5%, respectively, and well below the accepted thresholds for species and genus delineation. Phylogenomic analyses further supported their placement within a novel family of the order Halobacteriales. Based on phylogenetic, genomic, chemotaxonomic, and phenotypic analyses, these five strains represent two novel species of a novel genus within a novel family. The names, Halolitoreaceae fam. nov., Halolitoreus marinus gen. nov., sp. nov., and Halolitoreus rarus sp. nov. are herein proposed.

Coastal tidal flat↗

PubMed2004

Survey of archaeal diversity reveals an abundance of halophilic Archaea in a low-salt, sulfide- and sulfur-rich spring.

The archaeal community in a sulfide- and sulfur-rich spring with a stream water salinity of 0.7 to 1.0% in southwestern Oklahoma was studied by cloning and sequencing of 16S rRNA genes. Two clone libraries were constructed from sediments obtained at the hydrocarbon-exposed source of the spring and the microbial mats underlying the water flowing from the spring source. Analysis of 113 clones from the source library and 65 clones from the mat library revealed that the majority of clones belonged to the kingdom Euryarchaeota, while Crenarchaeota represented less than 10% of clones. Euryarchaeotal clones belonged to the orders Methanomicrobiales, Methanosarcinales, and Halobacteriales, as well as several previously described lineages with no pure-culture representatives. Those within the Halobacteriales represented 36% of the mat library and 4% of the source library. All cultivated members of this order are obligately aerobic halophiles. The majority of halobacterial clones encountered were not affiliated with any of the currently described genera of the family Halobacteriaceae. Measurement of the salinity at various locations at the spring, as well as along vertical gradients, revealed that soils adjacent to spring mats have a much higher salinity (NaCl concentrations as high as 32%) and a lower moisture content than the spring water, presumably due to evaporation. By use of a high-salt-plus-antibiotic medium, several halobacterial isolates were obtained from the microbial mats. Analysis of 16S rRNA genes indicated that all the isolates were members of the genus Haloferax. All isolates obtained grew at a wide range of salt concentrations, ranging from 6% to saturation, and all were able to reduce elemental sulfur to sulfide. We reason that the unexpected abundance of halophilic Archaea in such a low-salt, highly reduced environment could be explained by their relatively low salt requirement, which could be satisfied in specific locations of the shallow spring via evaporation, and their ability to grow under the prevalent anaerobic conditions in the spring, utilizing zero-valent sulfur compounds as electron acceptors. This study demonstrates that members of the Halobacteriales are not restricted to their typical high-salt habitats, and we propose a role for the Halobacteriales in sulfur reduction in natural ecosystems.

Archaea↗

PubMed2006

Evolution of a protein-folding machine: genomic and evolutionary analyses reveal three lineages of the archaeal hsp70(dnaK) gene.

The stress chaperone protein Hsp70 (DnaK) (abbreviated DnaK) and its co-chaperones Hsp40(DnaJ) (or DnaJ) and GrpE are universal in bacteria and eukaryotes but occur only in some archaea clustered in the order 5'-grpE-dnaK-dnaJ-3' in a locus termed Locus I. Three structural varieties of Locus I, termed Types I, II, and III, were identified, respectively, in Methanosarcinales, in Thermoplasmatales and Methanothermobacter thermoautotrophicus, and in Halobacteriales. These Locus I types corresponded to three groups identified by phylogenetic trees of archaeal DnaK proteins including the same archaeal subdivisions. These archaeal DnaK groups were not significantly interrelated, clustering instead with DnaKs from three bacterial lineages, Methanosarcinales with Firmicutes, Thermoplasmatales and M. thermoautotrophicus with Thermotoga, and Halobacteriales with Actinobacteria, suggesting that the three archaeal types of Locus I were acquired by independent events of lateral gene transfer. These associations, however, lacked strong bootstrap support and were sensitive to dataset choice and tree-reconstruction method. Structural features of dnaK loci in bacteria revealed that Methanosarcinales and Firmicutes shared a similar structure, also common to most other bacterial groups. Structural differences were observed instead in Thermotoga compared to Thermoplasmatales and M. thermoautotrophicus, and in Actinobacteria compared to Halobacteriales. It was also found that the association between the DnaK sequences from Halobacteriales and Actinobacteria likely reflects common biases in their amino acid compositions. Although the loci structural features and the DnaK trees suggested the possibility of lateral gene transfer between Firmicutes and Methanosarcinales, the similarity between the archaeal and the ancestral bacterial loci favors the more parsimonious hypothesis that all archaeal sequences originated from a unique prokaryotic ancestor.

Amino Acid Sequence↗

PubMed2002

Intracellular ion and organic solute concentrations of the extremely halophilic bacterium Salinibacter ruber.

Salinibacter ruber is a red obligatory aerobic chemoorganotrophic extremely halophilic Bacterium, related to the order Cytophagales. It was isolated from saltern crystallizer ponds, and requires at least 150 g l(-1) salt for growth. The cells have an extremely high potassium content, the ratio K(+)/protein being in the same range as in halophilic Archaea of the order Halobacteriales. X-ray microanalysis in the electron microscope of cells grown in medium of 250 g l(-1) salt confirmed the high intracellular K(+)concentrations, and showed intracellular chloride to be about as high as the cation concentrations within the cells. A search for intracellular organic osmotic solutes, using (13)C-NMR and HPLC techniques, showed glutamate, glycine betaine, and N-alpha-acetyllysine to be present in low concentrations only, contributing very little to the overall osmotic balance. The results presented suggest that the extremely halophilic Bacterium Salinibacteruses a similar mode of haloadaptation to that of the Archaea of the order Halobacteriales, and does not accumulate organic osmotic solutes such as are used by all other known halophilic and halotolerant aerobic Bacteria.

Bacteroidetes↗

PubMed2007

Haladaptatus paucihalophilus gen. nov., sp. nov., a halophilic archaeon isolated from a low-salt, sulfide-rich spring.

Two novel strains of halophilic archaea, DX253(T) and GY252, were isolated from Zodletone Spring, a low-salt, sulfide- and sulfur-rich spring in south-western Oklahoma, USA. The cells were cocci or coccobacilli and occurred singly or in pairs. The two strains grew in a wide range of salt concentrations (0.8-5.1 M) and required at least 5 mM Mg(2+) for growth. The pH range for growth was 5-7.5 and the temperature range was 25-45 degrees C. In addition to having the capacity to grow at relatively low salt concentrations, cells remained viable in distilled water after prolonged incubation. The two diether phospholipids that are typical of members of the order Halobacteriales, phosphatidylglycerol and phosphatidylglycerol phosphate methyl ester, were present. Phosphatidylglycerol sulfate and two unidentified glycolipids were also detected. Each strain had two distinct 16S rRNA gene sequences that were only 89.5-90.8 % similar to sequences from the most closely related cultured and recognized species within the order Halobacteriales. The DNA G+C content of the type strain was found to be 60.5 mol%. The closest relatives were clones and uncharacterized isolates obtained from coastal salt-marsh sediments with salinities equivalent to that of seawater. The physiological, biochemical and phylogenetic differences between strains DX253(T) and GY252 and other previously described genera of extremely halophilic archaea suggest that these novel strains represent a novel species and genus within the family Halobacteriaceae, for which the name Haladaptatus paucihalophilus gen. nov., sp. nov. is proposed. The type strain is DX253(T) (=JCM 13897(T)=DSM 18195(T)=ATCC BAA-1313(T)=KCTC 4006(T)).

DNA, Archaeal↗

PubMed2026

Ecological and evolutionary implications of a mobile genetic element-rich haloarchaeon with unique osmotic resilience.

We isolated a novel halophilic archaeon, strain DSL9, representing the proposed new species Haloliberatus hailidukes gen. nov., sp. nov., from Dishui Lake, China. Unlike most obligate halophiles, DSL9 survives in low salinity, even distilled water, without lysis. Genomic analysis revealed dual salinity adaptation strategies: salt-in and compatible solutes, including a complete trehalose biosynthesis pathway. The strain harbors multiple plasmids, notably a 111,311 bp large plasmid (pHdsl9-3) encoding replication (Orc1/Cdc6, SSB), transcription (TFIIB), transmission (T4SS cluster, ArdC-like protein), and recombination (XerA) modules. pHdsl9-3 provides auxiliary functions such as defense, genome diversification, ion detoxification, and suggests active horizontal gene transfer. Similar elements are widespread in Halobacteriales, highlighting their role in haloarchaeal genetic diversity and plasticity. The encoded XerA hinted at a function beyond DNA dimer resolution, suggesting it may have been adapted by other archaeal mobile genetic elements. These findings underscore the need to investigate plasmid-driven evolution and environmental adaptation mechanisms in haloarchaea.IMPORTANCEThis study reports the isolation and characterization of DSL9, a novel halophilic archaeon from a freshwater lake. Remarkably, DSL9 defies the typical obligate halophilic lifestyle by surviving in low-salinity environments, including distilled water, without cell lysis. A key discovery is the identification of a 111,311 bp large plasmid harboring essential modules for replication, transcription, transmission, and integration. Widespread distribution of similar elements across Halobacteriales suggests their crucial role in haloarchaeal genetic diversity and plasticity, warranting further study of plasmid-mediated evolution and adaptation strategies.

Lakes↗

PubMed2000

Haloterrigena thermotolerans sp. nov., a halophilic archaeon from Puerto Rico.

An extremely halophilic Archaeon belonging to the order Halobacteriales was isolated from the solar salterns of Cabo Rojo, Puerto Rico. The organism, designated strain PR5T, is rod-shaped, non-motile and requires at least 12% (w/v) NaCl to grow. The strain is highly thermotolerant: its temperature optimum is 50 degrees C and growth is possible up to 60 degrees C. Polar lipid analysis revealed the presence of the bis-sulfated glycolipid S2-DGD-1 as sole glycolipid and the absence of the glycerol diether analogue of phosphatidylglycerosulfate. Both C20,C20 and C20,C25 core lipids are present. The G+C content of the DNA is 63.3 mol%. According to 16S rDNA sequence data, strain PR5T is closely related to the representatives of the genera Haloterrigena and Natrinema, but on the basis of its phenotypic properties, 16S rDNA sequence and DNA-DNA hybridization studies, strain PR5T cannot be assigned to any of the recognized species within these genera. On the basis of its polar lipid composition, the isolate has been assigned to the genus Haloterrigena. The creation of a new species, Haloterrigena thermotolerans, is therefore proposed to accommodate this isolate. The type strain is strain PR5T (= DSM 11552T = ATCC 700275T).

Base Composition↗

PubMed2002

Updating carbamoylphosphate synthase (CPS) phylogenies: occurrence and phylogenetic identity of archaeal CPS genes.

Among Bacteria the carA and carB genes encoding the small (CarA) and large (CarB) subunits of carbamoylphosphate synthase (CPS) have been lost in certain symbionts (Haemophylus influenzae) and in most obligate intracellular parasites (Chlamydiae, Spirochaetes, Mycoplasmatales, Rickettsiae) having genome sizes in the 0.7- to 1.1-Mb range. Compared to Bacteria, Archaea exhibit a more varied pattern of CPS gene losses and an unusual propensity to incorporate CPS genes derived from both Bacteria and other Archaea. Schematically they fall into three groups. Group 1 taxa (the crenarchaeon Aeropyrum pernix and the euryarchaea Pyrococcus horikoshi and Pyrococcus abyssii) lack CPS genes altogether. Group 2 taxa (comprising Halobacteriales, Thermoplasmales, Methanococcales, Methanomicrobiales, Archaeoglobales) harbor CPS genes whose encoded CarB and CarA subunit proteins are ostensibly bacterial in origin; that is, they are intermixed with bacterial homologues on a phylogeny of concatenated CarA and CarB sequences and are not distinguishable from bacterial sequences after searching for domain-specific amino acid residue positions. Group 3 taxa (the crenarchaea Pyrobaculum aerophilum, Sulfolobus solfataricus, and Sulfolobus tokodaii and the euryarchaeon Pyrococcus furiosus) harbor CPS genes whose encoded proteins appear to be archaeal: consistent with an archaeal origin, the CarA and CarB sequences in this group possess both unique signatures and signatures affiliating them to Eukarya. Based on the topology of the clade comprising the four Group 3 taxa, we argue that CPS genes of P. furiosus (a euryarchaeon) and those of the crenarchaea P. aerophilum, S. solfataricus, and S. tokodaii are of a single type, resulting from the two genes being laterally transferred from a crenarchaeon to P. furiosus.

Amino Acid Motifs↗

PubMed2005

Proteomics of Halophilic archaea.

Halophilic archaea is a member of the Halobacteriacea family, the only family in the Halobacteriales order. Most Halophilic archaea require 1.5M NaCl both to grow and retain the structural integrity of the cells. The proteins of these organisms have thus been adapted to be active and stable in the hypersaline condition. Consequently, the unique properties of these biocatalysts have resulted in several novel applications in industrial processes. Halophilic archaea are also to be useful for bioremediation of hypersaline environment. Proteome data have expended enormously with the significant advance recently achieved in two-dimensional gel electrophoresis (2-DE) and mass spectrometry (MS). The whole genome sequencing of Halobacterium species NRC-1 was completed and this would also provide tremendous help to analyze the protein mass data from the similar strain Halobacterium salinarum. Proteomics coupled with genomic databases now has become a basic tool to understand or identify the function of genes and proteins. In addition, the bioinformatics approach will facilitate to predict the function of novel proteins of Halophilic archaea. This review will discuss current proteome study of Halophilic archaea and introduce the efficient procedures for screening, predicting, and confirming the function of novel halophilic enzymes.

Amino Acid Sequence↗

PubMed1998

Halogeometricum borinquense gen. nov., sp. nov., a novel halophilic archaeon from Puerto Rico.

A novel extremely halophilic archaeon was isolated from the solar salterns of Cabo Rojo, Puerto Rico. The organism is very pleomorphic, motile and requires at least 8% (w/v) NaCl to grow. Polar lipid composition revealed the presence of a novel non-sulfate-containing glycolipid and the absence of the glycerol diether analogue of phosphatidylglycerosulfate. The G + C content of the DNA is 59 mol%. On the basis of 16S rRNA sequence data, the new isolate cannot be classified in one of the recognized genera, but occupies a position that is distantly related to the genus Haloferax. All these features justify the creation of a new genus and a new species for the family Halobacteriaceae, order Halobacteriales. The name Halogeometricum borinquense gen. nov., sp. nov. is proposed. The type strain is ATCC 700274T.

Base Composition↗

PubMed2004

Halorubrum tibetense sp. nov., a novel haloalkaliphilic archaeon from Lake Zabuye in Tibet, China.

A novel haloalkaliphilic archaeon, strain 8W8T, was isolated from Lake Zabuye, on the Tibetan Plateau, China. On the basis of 16S rRNA gene sequence analysis, strain 8W8T was shown to belong to the genus Halorubrum and was related to Halorubrum vacuolatum (96.7% sequence similarity), Halorubrum saccharovorum (96.0%), Halorubrum lacusprofundi (95.4%) and Halorubrum sodomense (95.3%). The phylogenetic distance from any species within the other genera of Halobacteriales was lower than 90%. The major polar lipids of strain 8W8T were C20C20 and C20C25 derivatives of phosphatidylglycerol phosphate and phosphatidylglycerol phosphate methyl ester. The results of DNA-DNA hybridization and physiological and biochemical tests allowed genotypic and phenotypic differentiation of strain 8W8T from the eight Halorubrum species with validly published names. Therefore, strain 8W8T represents a novel species, for which the name Halorubrum tibetense sp. nov. is proposed, with the type strain 8W8T (=AS 1.3239T=JCM 11889T).

China↗

PubMed2006

Halostagnicola larsenii gen. nov., sp. nov., an extremely halophilic archaeon from a saline lake in Inner Mongolia, China.

Strain XH-48(T) was isolated from the sediment of Lake Xilinhot, a saline lake in Inner Mongolia (China). The organism is pleomorphic, neutrophilic and requires at least 2.5 M (15 %) NaCl, but not MgCl(2), for growth; it exhibits optimal growth at 3.4 M (20 %) NaCl. The G+C content of its DNA is 61 mol%. 16S rRNA gene sequence analysis revealed that strain XH-48(T) is a member of the family Halobacteriaceae, but there were low levels of similarity with other members of this family. The highest sequence similarity values (94.5 and 93.3 %) were obtained with the 16S rRNA genes of Natrialba aegyptiaca and Natrialba asiatica, respectively. Polar lipid analyses revealed that strain XH-48(T) contains phosphatidylglycerol and phosphatidylglyceromethylphosphate, derived from both C(20)C(20) and C(20)C(25) glycerol diethers, and two unidentified glycolipids. On the basis of the data obtained, the novel isolate cannot be classified within any recognized genus. Strain XH-48(T) should be placed within a novel genus and species within the family Halobacteriaceae, order Halobacteriales, for which the name Halostagnicola larsenii gen. nov., sp. nov. is proposed. The type strain of Halostagnicola larsenii is strain XH-48(T) (=DSM 17691(T)=CGMCC 1.5338(T)=JCM 13463(T)=CECT 7116(T)).

Aerobiosis↗

PubMed2004

Origins and evolution of isoprenoid lipid biosynthesis in archaea.

A characteristic feature of the domain archaea are the lipids forming the hydrophobic core of their cell membrane. These unique lipids are composed of isoprenoid side-chains stereospecifically ether linked to sn-glycerol-1-phosphate. Recently, considerable progress has been made in characterizing the enzymes responsible for the synthesis of archaeal lipids. However, little is known about their evolution. To better understand how this unique biosynthetic apparatus came to be, large-scale database surveys and phylogenetic analyses were performed. All characterized enzymes involved in the biosynthesis of isoprenoid side-chains and the glycerol phosphate backbone along with their assembly in ether lipids were included in these analyses. The sequence data available in public databases was complemented by an in-depth sampling of isoprenoid lipid biosynthesis genes from multiple genera of the archaeal order Halobacteriales, allowing us to look at the evolution of these enzymes on a smaller phylogenetic scale. This investigation of the isoprenoid biosynthesis apparatus of archaea on small and large phylogenetic scales reveals that it evolved through a combination of evolutionary processes, including the co-option of ancestral enzymes, modification of enzymatic specificity, orthologous and non-orthologous gene displacement, integration of components from eukaryotes and bacteria and lateral gene transfer within and between archaeal orders.

Alkyl and Aryl Transferases↗

PubMed2007

Characterization of the prokaryotic diversity in cold saline perennial springs of the Canadian high Arctic.

The springs at Gypsum Hill and Colour Peak on Axel Heiberg Island in the Canadian Arctic originate from deep salt aquifers and are among the few known examples of cold springs in thick permafrost on Earth. The springs discharge cold anoxic brines (7.5 to 15.8% salts), with a mean oxidoreduction potential of -325 mV, and contain high concentrations of sulfate and sulfide. We surveyed the microbial diversity in the sediments of seven springs by denaturing gradient gel electrophoresis (DGGE) and analyzing clone libraries of 16S rRNA genes amplified with Bacteria and Archaea-specific primers. Dendrogram analysis of the DGGE banding patterns divided the springs into two clusters based on their geographic origin. Bacterial 16S rRNA clone sequences from the Gypsum Hill library (spring GH-4) were classified into seven phyla (Actinobacteria, Bacteroidetes, Firmicutes, Gemmatimonadetes, Proteobacteria, Spirochaetes, and Verrucomicrobia); Deltaproteobacteria and Gammaproteobacteria sequences represented half of the clone library. Sequences related to Proteobacteria (82%), Firmicutes (9%), and Bacteroidetes (6%) constituted 97% of the bacterial clone library from Colour Peak (spring CP-1). Most GH-4 archaeal clone sequences (79%) were related to the Crenarchaeota while half of the CP-1 sequences were related to orders Halobacteriales and Methanosarcinales of the Euryarchaeota. Sequences related to the sulfur-oxidizing bacterium Thiomicrospira psychrophila dominated both the GH-4 (19%) and CP-1 (45%) bacterial libraries, and 56 to 76% of the bacterial sequences were from potential sulfur-metabolizing bacteria. These results suggest that the utilization and cycling of sulfur compounds may play a major role in the energy production and maintenance of microbial communities in these unique, cold environments.

Archaea↗

PubMed2006

Microbial diversity in water and sediment of Lake Chaka, an athalassohaline lake in northwestern China.

We employed culture-dependent and -independent techniques to study microbial diversity in Lake Chaka, a unique hypersaline lake (32.5% salinity) in northwest China. It is situated at 3,214 m above sea level in a dry climate. The average water depth is 2 to 3 cm. Halophilic isolates were obtained from the lake water, and halotolerant isolates were obtained from the shallow sediment. The isolates exhibited resistance to UV and gamma radiation. Microbial abundance in the sediments ranged from 10(8) cells/g at the water-sediment interface to 10(7) cells/g at a sediment depth of 42 cm. A major change in the bacterial community composition was observed across the interface. In the lake water, clone sequences affiliated with the Bacteroidetes were the most abundant, whereas in the sediments, sequences related to low G+C gram-positive bacteria were predominant. A similar change was also present in the archaeal community. While all archaeal clone sequences in the lake water belonged to the Halobacteriales, the majority of the sequences in the sediments were related to those previously obtained from methanogenic soils and sediments. The observed changes in the microbial community structure across the water-sediment interface were correlated with a decrease in salinity from the lake water (32.5%) to the sediments (approximately 4%). Across the interface, the redox state also changed from oxic to anoxic and may also have contributed to the observed shift in the microbial community.

Bacteroides↗