Haloplanus natans gen. nov., sp. nov., an extremely halophilic, gas-vacuolate archaeon isolated from Dead Sea-Red Sea water mixtures in experimental outdoor ponds

Genome-based classification of the class Halobacteria and description of Haladaptataceae fam. nov. and Halorubellaceae fam. nov

Currently, there are four mainstream taxonomic opinions on the classification of the class Halobacteria at the family and order levels. The International Committee on Systematics of Prokaryotes Subcommittee on the Taxonomy of Halobacteria (ICSP), List of Prokaryotic names with Standing in Nomenclature (LPSN) and National Centre for Biotechnology Information (NCBI) adopted taxonomies have three to four orders and up to eight families, while the Genome Taxonomy Database (GTDB) taxonomy proposes only one order with nine families. To resolve the taxonomic inconsistency, phylogenomic analyses based on concatenated single-copy orthologous proteins and 122 concatenated conserved single-copy marker proteins were conducted to infer the taxonomic status of the current representatives of the class Halobacteria at the family and order levels. The current 76 genera with validly published names of the class Halobacteria were able to be assigned into eight families in one order. On the basis of these results, it is proposed that the current species with validly published names of the class Halobacteria should be remerged into the order Halobacteriales, then assigned to eight families, Haladaptataceae, Haloarculaceae, Halobacteriaceae, Halococcaceae, Haloferacaceae, Natronoarchaeaceae, Natrialbaceae and Halorubellaceae. Thus, Haladaptataceae fam. nov. is described based on Haladaptatus, Halomicrococcus and Halorussus and Halorubellaceae fam. nov. is proposed incorporating Haloarchaeobius and Halorubellus, respectively.

Vertical organization of microbial communities in Salineta hypersaline wetland, Spain

Microbial communities inhabiting hypersaline wetlands, well adapted to the environmental fluctuations due to flooding and desiccation events, play a key role in the biogeochemical cycles, ensuring ecosystem service. To better understand the ecosystem functioning, we studied soil microbial communities of Salineta wetland (NE Spain) in dry and wet seasons in three different landscape stations representing situations characteristic of ephemeral saline lakes: S1 soil usually submerged, S2 soil intermittently flooded, and S3 soil with halophytes. Microbial community composition was determined according to different redox layers by 16S rRNA gene barcoding. We observed reversed redox gradient, negative at the surface and positive in depth, which was identified by PERMANOVA as the main factor explaining microbial distribution. The Pseudomonadota, Gemmatimonadota, Bacteroidota, Desulfobacterota, and Halobacteriota phyla were dominant in all stations. Linear discriminant analysis effect size (LEfSe) revealed that the upper soil surface layer was characterized by the predominance of operational taxonomic units (OTUs) affiliated to strictly or facultative anaerobic halophilic bacteria and archaea while the subsurface soil layer was dominated by an OTU affiliated to Roseibaca, an aerobic alkali-tolerant bacterium. In addition, the potential functional capabilities, inferred by PICRUSt2 analysis, involved in carbon, nitrogen, and sulfur cycles were similar in all samples, irrespective of the redox stratification, suggesting functional redundancy. Our findings show microbial community changes according to water flooding conditions, which represent useful information for biomonitoring and management of these wetlands whose extreme aridity and salinity conditions are exposed to irreversible changes due to human activities.

Limitation of Microbial Processes at Saturation-Level Salinities in a Microbial Mat Covering a Coastal Salt Flat

Hypersaline microbial mats are dense microbial ecosystems capable of performing complete element cycling and are considered analogs of early Earth and hypothetical extraterrestrial ecosystems. We studied the functionality and limits of key biogeochemical processes, such as photosynthesis, aerobic respiration, and sulfur cycling, in salt crust-covered microbial mats from a tidal flat at the coast of Oman. We measured light, oxygen, and sulfide microprofiles as well as sulfate reduction rates at salt saturation and in flood conditions and determined fine-scale stratification of pigments, biomass, and microbial taxa in the resident microbial community. The salt crust did not protect the mats against irradiation or evaporation. Although some oxygen production was measurable at salinities of ≤30% (wt/vol) in situ, at saturation-level salinity (40%), oxygenic photosynthesis was completely inhibited and only resumed 2 days after reducing the porewater salinity to 12%. Aerobic respiration and active sulfur cycling occurred at low rates under salt saturation and increased strongly upon salinity reduction. Apart from high relative abundances of Chloroflexi, photoheterotrophic Alphaproteobacteria, Bacteroidetes, and Archaea, the mat contained a distinct layer harboring filamentous Cyanobacteria, which is unusual for such high salinities. Our results show that the diverse microbial community inhabiting this salt flat mat ultimately depends on periodic salt dilution to be self-sustaining and is rather adapted to merely survive salt saturation than to thrive under the salt crust. IMPORTANCE Due to their abilities to survive intense radiation and low water availability, hypersaline microbial mats are often suggested to be analogs of potential extraterrestrial life. However, even the limitations imposed on microbial processes by saturation-level salinity found on Earth have rarely been studied in situ. While abundance and diversity of microbial life in salt-saturated environments are well documented, most of our knowledge on process limitations stems from culture-based studies, few in situ studies, and theoretical calculations. In particular, oxygenic photosynthesis has barely been explored beyond 5 M NaCl (28% wt/vol). By applying a variety of biogeochemical and molecular methods, we show that despite abundance of photoautotrophic microorganisms, oxygenic photosynthesis is inhibited in salt-crust-covered microbial mats at saturation salinities, while rates of other energy generation processes are decreased several-fold. Hence, the complete element cycling required for self-sustaining microbial communities only occurs at lower salt concentrations.

DNA metabarcoding illustrates biological pollution threats of Red Sea - Dead Sea water conveyance to Dead Sea biodiversity

The Dead Sea has a hypersaline environment where only extremophile species like Archaea, Bacteria, and fungi can survive. The Red Sea-Dead Sea Water Conveyance (RDSC) is constructing a pipeline of 180 km to import water from the Red Sea in the shrinking Dead Sea. Both seas exhibit highly different hydrographic features that determine their biodiversity. Using environmental DNA (eDNA) metabarcoding and amplifying a fragment of the cytochrome oxidase subunit I gene (COI) from water samples, we compared the communities of the Red Sea and the Dead Sea to understand the potential impact of the water conveyance project on biodiversity, following by an identification of potential biopollutants able to enter the Dead Sea for their small size. The results suggest a high likelihood of acquiring harmful algae into the Dead Sea. This study alerts about the real risk of losing the unique Dead Sea biota when the conveyance is actually undertaken.

Cultivation of halophilic archaea (class Halobacteria) from thalassohaline and athalassohaline environments

As a group, the halophilic archaea (class Halobacteria) are the most salt-requiring and salt-resistant microorganisms within the domain Archaea. Halophilic archaea flourish in thalassohaline and athalassohaline environments and require over 100-150 g/L NaCl for growth and structural stability. Natural hypersaline environments vary in salt concentration, chemical composition and pH, and occur in climates ranging from tropical to polar and even under-sea. Accordingly, their resident haloarchaeal species vary enormously, as do their individual population compositions and community structures. These diverse halophilic archaeal strains are precious resources for theoretical and applied research but assessing their taxonomic and metabolic novelty and diversity in natural environments has been technically difficult up until recently. Environmental DNA-based high-throughput sequencing technology has now matured sufficiently to allow inexpensive recovery of massive amounts of sequence data, revealing the distribution and community composition of halophilic archaea in different hypersaline environments. While cultivation of haloarchaea is slow and tedious, and only recovers a fraction of the natural diversity, it is the conventional means of describing new species, and provides strains for detailed study. As of the end of May 2020, the class Halobacteria contains 71 genera and 275 species, 49.8% of which were first isolated from the marine salt environment and 50.2% from the inland salt environment, indicating that both thalassohaline and athalassohaline environments contain diverse halophilic archaea. However, there remain taxa that have not yet been isolated in pure culture, such as the nanohaloarchaea, which are widespread in the salt environment and may be one of the hot spots in the field of halophilic archaea research in the future. In this review, we focus on the cultivation strategies that have been used to isolate extremely halophilic archaea and point out some of the pitfalls and challenges.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42995-020-00087-3.

Halobellus ruber sp. nov., a deep red-pigmented extremely halophilic archaeon isolated from a Korean solar saltern

A novel halophilic archaeon, strain MBLA0160^T, was isolated from a solar saltern in Sorae, Republic of Korea. The cells are deep-red pigmented, Gram-negative, rod shaped, motile, and lysed in distilled water. The strain MBLA0160^T grew at 25-45 °C (optimum 37 °C), in 15-30% (w/v) NaCl (optimum 20%) and 0.1-1.0 M MgCl₂ (optimum 0.3-0.5 M) at pH 5.0-9.0 (optimum 7.0). Phylogenetic analysis based on the 16S rRNA sequence showed that this strain was related to two species within the genus Halobellus (Hbs.), with 98.4% and 95.8% similarity to Hbs. salinus CSW2.24.4 ^T and Hbs. clavatus TNN18^T, respectively. The major polar lipids of the strain MBLA160^T were phosphatidylglycerol, phosphatidylglycerol sulfate, and phosphatidylglycerol phosphate methyl ester. The genome size, G + C content, and N50 value of MBLA0160^T were 3.49 Mb, 66.5 mol%, and 620,127 bp, respectively. According to predicted functional proteins of strain MBLA0160^T, the highest category was amino acid transport and metabolism. Genome rapid annotation showed that amino acid and derivatives was the most subsystem feature counts. Pan-genomic analysis showed that strain MBLA0160^T had 97 annotated unique KEGG, which were mainly included metabolism and environmental information processing. Ortholog average nucleotide identities (OrthoANI) and in silico DNA-DNA hybridization (isDDH) values between the strain MBLA0160^T and other strains of the genus Halobellus were under 84,4% and 28.1%, respectively. The genome of strain MBLA0160^T also contain the biosynthetic gene cluster for C₅₀ carotenoid as secondary metabolite. Based on the phylogenetic, phenotypic, chemotaxonomic properties, and comparative genomic analyses, strain MBLA0160^T is considered to represent a novel species of the genus Halobellus, for which the name Halobellus ruber sp. nov. is proposed. The type strain is MBLA0160^T (= KCTC 4291 ^T = JCM 34172 ^T).

Halalkalirubrum salinum gen. nov., sp. nov., a halophilic archaeon isolated from a saline lake

A novel extremely halophilic archaeon, strain N1521^T, was isolated from a saline lake in Tibet, China. Cells of the strain were pleomorphic and Gram-stain-negative. It produced red pigments. Growth was observed at 4-42 °C (optimum, 37 °C), pH 7.0-10.5 (optimum, 8.0-9.5), NaCl 11%-25% (optimum, 15%) and in the presence of 0-0.1 M MgCl₂ (optimum, 0.05 M) in aerobic conditions. The minimum NaCl concentration that prevented cell lysis was 2% (w/v). The major polar lipids of strain N1521^T were phosphatidylglycerol sulfate, phosphatidylglycerol phosphate methyl ester, phosphatidylglycerol and an unidentified glycolipid. The DNA G + C content was 58.37 mol%. According to 16S rRNA gene sequence comparisons, strain N1521^T revealed the highest sequence similarity to Haloprofundus halophilus NK23^T (91.38%) and Halogranum amylolyticum TNN58^T (91.00%), and low sequence similarities (< 91%) with other genera in the order Haloferacales. Phylogenetic analysis based on the 16S rRNA gene and rpoB' gene sequence showed that strain N1521^T was distinct from the members of the order Haloferacales. The digital DNA-DNA hybridization, average nucleotide identity and average amino acid identity values calculated from whole genome-sequence comparison between strain N1521^T and the members of the order Haloferacales were in the ranges of 15.1-18.2%, 68.8-73.0%, and 58.4-63.9%, respectively. Phylogenetic tree reconstructions based on the whole-genome sequences revealed that strain N1521^T was closer to the members of the family Halorubraceae. Based on the data obtained, strain N1521^T is thus considered to represent a novel species of a new genus within the family Halorubraceae, for which the name Halalkalirubrum salinum gen. nov., sp. nov. is proposed. The type strain is N1521^T (= CGMCC 1.16693 = JCM 33785).

Haloplanus rubicundus sp. nov., an extremely halophilic archaeon isolated from solar salt

Two extremely halophilic archaea strains, CBA1112^T and CBA1113, were isolated from solar salt in Korea. The genome sizes and G+C content of CBA1112^T and CBA1113 were 3.77 and 3.53Mb, and 66.0 and 66.5mol%, respectively. Phylogenetic analysis based on closely related taxa and environmental Haloplanus sequences indicated that both CBA1112^T and CBA1113 strains are grouped within the genus Haloplanus. OrthoANI and in silico DNA-DNA hybridization values were below the species delineation threshold. Pan-genomic analysis showed that the two novel strains and four reference strains had 6203 pan-orthologous groups in total. Six Haloplanus strains shared 1728 core pan-genome orthologous groups, which were mainly associated with amino acid transport and metabolism and translation, ribosomal structure and biogenesis categories, and amino acid metabolism and carbohydrate metabolism related categories. The novel strain-specific pan-genome orthologous groups were mainly involved with replication, recombination and repair category and replication and repair pathway or amino acid metabolism pathway. Cells of both strains were Gram-negative and pleomorphic, and colonies were red-pigmented. The major polar lipids of both strains were phosphatidylglycerol, phosphatidylglycerol phosphate methyl ester, phosphatidylglycerol sulfate, and one glycolipid, sulfated mannosyl glucosyl diether. Based on genomic, phylogenetic, phenotypic, and chemotaxonomic features, strains CBA1112^T and CBA1113 are described as novel species of the genus Haloplanus. Thus, we propose the name Haloplanus rubicundus sp. nov. The type strain is CBA1112^T (=KCCM 43224^T=JCM 30475^T).

Haloplanus salinarum sp. nov., an extremely halophilic archaeon isolated from a solar saltern

An extremely halophilic archaeal strain SP28^T was isolated from the Gomso solar saltern, Republic of Korea. Cells of the new strain SP28^T were pleomorphic and Gram stain negative, and produced red-pigmented colonies. These grew in medium with 2.5-4.5 M NaCl (optimum 3.1 M) and 0.05-0.5 M MgCl2 (optimum 0.1 M), at 25-50 °C (optimum 37 °C) and at a pH of 6.5-8.5 (optimum pH 8.0). Mg²⁺ was required for growth. A concentration of at least 2 M NaCl was required to prevent cell lysis. Polar lipids included phosphatidylglycerol, phosphatidylglycerol phosphate methyl ester, phosphatidylglycerol sulfate and one glycolipid chromatographically identical to sulfated mannosyl glucosyl diether. 16S rRNA and rpoB' gene sequence analyses showed that strain SP28^T is closely related to Haloplanus ruber R35^T (97.3 and 94.1 %, 16S rRNA and rpoB' gene sequence similarity, respectively), Haloplanus litoreus GX21^T (97.0 and 92.1 %), Haloplanus salinus YGH66^T (96.0 and 91.9 %), Haloplanus vescus RO5-8^T (95.9 and 90.9 %), Haloplanus aerogenes TBN37^T (95.6 and 90.3 %) and Haloplanus natans RE-101^T (95.3 and 89.8 %). The DNA G+C content of the novel strain SP28^T was 66.2 mol%, which is slightly higher than that of Hpn.litoreus GX21^T (65.8 mol%) and Hpn.ruber R35^T (66.0 mol%). DNA-DNA hybridization values betweenHpn.ruber R35^T and strain SP28^T and between Hpn.litoreus GX21^T and strain SP28^T were about 24.8 and 20.7 %, respectively. We conclude that strain SP28^T represents a novel species of the genus Haloplanus and propose the name Haloplanus salinarum sp. nov. The type strain is SP28^T (=JCM 31424^T=KCCM 43210^T).

Systematics of haloarchaea and biotechnological potential of their hydrolytic enzymes

Halophilic archaea, also referred to as haloarchaea, dominate hypersaline environments. To survive under such extreme conditions, haloarchaea and their enzymes have evolved to function optimally in environments with high salt concentrations and, sometimes, with extreme pH and temperatures. These features make haloarchaea attractive sources of a wide variety of biotechnological products, such as hydrolytic enzymes, with numerous potential applications in biotechnology. The unique trait of haloarchaeal enzymes, haloenzymes, to sustain activity under hypersaline conditions has extended the range of already-available biocatalysts and industrial processes in which high salt concentrations inhibit the activity of regular enzymes. In addition to their halostable properties, haloenzymes can also withstand other conditions such as extreme pH and temperature. In spite of these benefits, the industrial potential of these natural catalysts remains largely unexplored, with only a few characterized extracellular hydrolases. Because of the applied impact of haloarchaea and their specific ability to live in the presence of high salt concentrations, studies on their systematics have intensified in recent years, identifying many new genera and species. This review summarizes the current status of the haloarchaeal genera and species, and discusses the properties of haloenzymes and their potential industrial applications.

Haloprofundus marisrubri gen. nov., sp. nov., an extremely halophilic archaeon isolated from a brine-seawater interface

We isolated a Gram-stain-negative, pink-pigmented, motile, pleomorphic, extremely halophilic archaeon from the brine-seawater interface of Discovery Deep in the Saudi Arabian Red Sea. This strain, designated SB9T, was capable of growth within a wide range of temperatures and salinity, but required MgCl2. Cells lysed in distilled water, but at 7.0 % (w/v) NaCl cell lysis was prevented. The major polar lipids from strain SB9T were phosphatidylglycerol, phosphatidylglycerolphosphate methyl ester, sulfated mannosyl glucosyl diether, mannosyl glucosyl diether, an unidentified glycolipid and two unidentified phospholipids. The major respiratory quinones of strain SB9T were menaquinones MK8 (66 %) and MK8 (VIII-H2) (34 %). Analysis of the 16S rRNA gene sequence revealed that strain SB9T was closely related to species in the genera Halogranum and Haloplanus; in particular, it shared highest sequence similarity with the type strain of Halogranum rubrum (93.4 %), making it its closest known relative. The unfinished draft genome of strain SB9Twas 3 931 127 bp in size with a total G+C content of 62.53 mol% and contained 3917 ORFs, 50 tRNAs and eight rRNAs. Based on comparisons with currently available genomes, the highest average nucleotide identity value was 83 % to Halogranum salarium B-1T (GenBank accession no. GCA_000283335.1). These data indicate that this new isolate cannot be classified into any recognized genera of the family Haloferacaceae, and therefore strain SB9T is considered to be a representative of a novel species of a new genus within this family, for which the name Haloprofundus marisrubri gen. nov., sp. nov. is proposed. The type strain of Haloprofundus marisrubri is SB9T (=JCM 19565T=CGMCC 1.14959T).

Important roles for membrane lipids in haloarchaeal bioenergetics

Recent advances in lipidomic analysis in combination with various physiological experiments set the stage for deciphering the structure-function of haloarchaeal membrane lipids. Here we focused primarily on changes in lipid composition of Haloferax volcanii, but also performed a comparative analysis with four other haloarchaeal species (Halobacterium salinarum, Halorubrum lacusprofundi, Halorubrum sodomense and Haloplanus natans) all representing distinctive cell morphologies and behaviors (i.e., rod shape vs. pleomorphic behavior). Common to all five haloarchaea, our data reveal an extraordinary high level of menaquinone, reaching up to 72% of the total lipids. This ubiquity suggests that menaquinones may function beyond their ordinary role as electron and proton transporter, acting simultaneously as ion permeability barriers and as powerful shield against oxidative stress. In addition, we aimed at understanding the role of cations interacting with the characteristic negatively charged surface of haloarchaeal membranes. We propose for instance that by bridging the negative charges of adjacent anionic phospholipids, Mg²⁺ acts as surrogate for cardiolipin, a molecule that is known to control curvature stress of membranes. This study further provides a bioenergetic perspective as to how haloarchaea evolved following oxygenation of Earth's atmosphere. The success of the aerobic lifestyle of haloarchaea includes multiple membrane-based strategies that successfully balance the need for a robust bilayer structure with the need for high rates of electron transport - collectively representing the molecular basis to inhabit hypersaline water bodies around the planet.

Preservation of ancestral Cretaceous microflora recovered from a hypersaline oil reservoir

Microbiology of a hypersaline oil reservoir located in Central Africa was investigated with molecular and culture methods applied to preserved core samples. Here we show that the community structure was partially acquired during sedimentation, as many prokaryotic 16S rRNA gene sequences retrieved from the extracted DNA are phylogenetically related to actual Archaea inhabiting surface evaporitic environments, similar to the Cretaceous sediment paleoenvironment. Results are discussed in term of microorganisms and/or DNA preservation in such hypersaline and Mg-rich solutions. High salt concentrations together with anaerobic conditions could have preserved microbial/molecular diversity originating from the ancient sediment basin wherein organic matter was deposited.

Phylogenomic analyses and molecular signatures for the class Halobacteria and its two major clades: a proposal for division of the class Halobacteria into an emended order Halobacteriales and two new orders, Haloferacales ord. nov. and Natrialbales ord. nov., containing the novel families Haloferacaceae fam. nov. and Natrialbaceae fam. nov

The Halobacteria constitute one of the largest groups within the Archaea. The hierarchical relationship among members of this large class, which comprises a single order and a single family, has proven difficult to determine based upon 16S rRNA gene trees and morphological and physiological characteristics. This work reports detailed phylogenetic and comparative genomic studies on >100 halobacterial (haloarchaeal) genomes containing representatives from 30 genera to investigate their evolutionary relationships. In phylogenetic trees reconstructed on the basis of 32 conserved proteins, using both neighbour-joining and maximum-likelihood methods, two major clades (clades A and B) encompassing nearly two-thirds of the sequenced haloarchaeal species were strongly supported. Clades grouping the same species/genera were also supported by the 16S rRNA gene trees and trees for several individual highly conserved proteins (RpoC, EF-Tu, UvrD, GyrA, EF-2/EF-G). In parallel, our comparative analyses of protein sequences from haloarchaeal genomes have identified numerous discrete molecular markers in the form of conserved signature indels (CSI) in protein sequences and conserved signature proteins (CSPs) that are found uniquely in specific groups of haloarchaea. Thirteen CSIs in proteins involved in diverse functions and 68 CSPs that are uniquely present in all or most genome-sequenced haloarchaea provide novel molecular means for distinguishing members of the class Halobacteria from all other prokaryotes. The members of clade A are distinguished from all other haloarchaea by the unique shared presence of two CSIs in the ribose operon protein and small GTP-binding protein and eight CSPs that are found specifically in members of this clade. Likewise, four CSIs in different proteins and five other CSPs are present uniquely in members of clade B and distinguish them from all other haloarchaea. Based upon their specific clustering in phylogenetic trees for different gene/protein sequences and the unique shared presence of large numbers of molecular signatures, members of clades A and B are indicated to be distinct from all other haloarchaea because of their uniquely shared evolutionary histories. Based upon these results, it is proposed that clades A and B be recognized as two new orders, Natrialbales ord. nov. and Haloferacales ord. nov., within the class Halobacteria, containing the novel families Natrialbaceae fam. nov. and Haloferacaceae fam. nov. Other members of the class Halobacteria that are not members of these two orders will remain part of the emended order Halobacteriales in an emended family Halobacteriaceae.

Archaeal populations in two distinct sedimentary facies of the subsurface of the Dead Sea

Archaeal metabolism was studied in aragonitic and gypsum facies of the Dead Sea subsurface using high-throughput DNA sequencing. We show that the communities are well adapted to the peculiar environment of the Dead Sea subsurface. They harbor the necessary genes to deal with osmotic pressure using high- and low-salt-in strategies, and to cope with unusually high concentrations of heavy metals. Methanogenesis was identified for the first time in the Dead Sea and appears to be an important metabolism in the aragonite sediment. Fermentation of residual organic matter, probably performed by some members of the Halobacteria class is common to both types of sediments. The latter group represents more than 95% of the taxonomically identifiable Archaea in the metagenome of the gypsum sediment. The potential for sulfur reduction has also been revealed and is associated in the sediment with EPS degradation and Fe-S mineralization as revealed by SEM imaging. Overall, we show that distinct communities of Archaea are associated with the two different facies of the Dead Sea, and are adapted to the harsh chemistry of its subsurface, in different ways.

Impacts of restoration of an uncontrolled phosphogypsum dumpsite on the seasonal distribution of abiotic variables, phytoplankton, copepods, and ciliates in a man-made solar saltern

The restoration of an uncontrolled phosphogypsum landfill was investigated for its effects on the seasonal distribution of phytoplankton, ciliates, and copepods. Sampling was carried out monthly from September 2007 to August 2008 at four ponds of increasing salinity (A1, 41 psu; A5, 46 psu; A16, 67 psu; and C31, 77 psu) in the Sfax solar saltern (southeastern Tunisia). Physicochemical and biological analyses were carried out using standard methods. Results showed drastic reduction of phosphate input and greater diversity of phytoplankton, ciliates, and copepods than before restoration. Pennate diatoms and new ciliates, considered bio-indicators of less-stressed marine ecosystems, proliferated in the A1 pond for the first time after restoration. Copepods appeared to feed on a wide range of prey. Economically, removal of the 1.7 million m(3) of phosphate improved the quality of the site's salt production, enabling the salt company to receive the quality ISO 9001 accreditation.

The function of gas vesicles in halophilic archaea and bacteria: theories and experimental evidence

A few extremely halophilic Archaea (Halobacterium salinarum, Haloquadratum walsbyi, Haloferax mediterranei, Halorubrum vacuolatum, Halogeometricum borinquense, Haloplanus spp.) possess gas vesicles that bestow buoyancy on the cells. Gas vesicles are also produced by the anaerobic endospore-forming halophilic Bacteria Sporohalobacter lortetii and Orenia sivashensis. We have extensive information on the properties of gas vesicles in Hbt. salinarum and Hfx. mediterranei and the regulation of their formation. Different functions were suggested for gas vesicle synthesis: buoying cells towards oxygen-rich surface layers in hypersaline water bodies to prevent oxygen limitation, reaching higher light intensities for the light-driven proton pump bacteriorhodopsin, positioning the cells optimally for light absorption, light shielding, reducing the cytoplasmic volume leading to a higher surface-area-to-volume ratio (for the Archaea) and dispersal of endospores (for the anaerobic spore-forming Bacteria). Except for Hqr. walsbyi which abounds in saltern crystallizer brines, gas-vacuolate halophiles are not among the dominant life forms in hypersaline environments. There only has been little research on gas vesicles in natural communities of halophilic microorganisms, and the few existing studies failed to provide clear evidence for their possible function. This paper summarizes the current status of the different theories why gas vesicles may provide a selective advantage to some halophilic microorganisms.

Halopenitus persicus gen. nov., sp. nov., an archaeon from an inland salt lake

A novel pale pink-pigmented halophilic archaeon, strain DC30T, was isolated from Aran-Bidgol salt lake, a hypersaline playa in Iran. Cells of strain DC30T were non-motile and pleomorphic, from rods to triangular or disc-shaped. Strain DC30T required at least 1.7 M NaCl and 0.05 M MgCl2 for growth (optimum, 3 M NaCl and 0.1 M MgCl2). The optimum pH and temperature for growth of strain DC30T were pH 7.5 and 40 °C, respectively, although it was capable of growth over pH and temperature ranges of 6.5–8.5 and 25–50 °C, respectively. Analysis of the 16S rRNA gene sequence showed that strain DC30T was a member of the family Halobacteriaceae . However, it had low 16S rRNA gene sequence similarities of 92.4 %, 89.4 % and 89.1 % to the most closely related haloarchaeal taxa, the type species of the genera Halorubrum , Halogranum and Haloplanus , respectively. The DNA G+C content was 66.0 mol%. Phosphatidylglycerol and phosphatidylglycerol phosphate methyl ester, common phospholipids found in haloarchaea, were present. Three minor phospholipids and one unidentified glycolipid were also observed. The only quinone present was MK-8(II-H2). The physiological, biochemical and phylogenetic differences between strain DC30T and other previously described genera of extremely halophilic archaea suggest that strain DC30T represents a novel species in a new genus within the family Halobacteriaceae , for which the name Halopenitus persicus gen. nov., sp. nov. is proposed. The type strain of Halopenitus persicus is DC30T ( = IBRC 10041T = KCTC 4046T).

Phylogenetic diversities and community structure of members of the extremely halophilic Archaea (order Halobacteriales) in multiple saline sediment habitats

We investigated the phylogenetic diversity and community structure of members of the halophilic Archaea (order Halobacteriales) in five distinct sediment habitats that experience various levels of salinity and salinity fluctuations (sediments from Great Salt Plains and Zodletone Spring in Oklahoma, mangrove tree sediments in Puerto Rico, sediment underneath salt heaps in a salt-processing plant, and sediments from the Great Salt Lake northern arm) using Halobacteriales-specific 16S rRNA gene primers. Extremely diverse Halobacteriales communities were encountered in all habitats, with 27 (Zodletone) to 37 (mangrove) different genera identified per sample, out of the currently described 38 Halobacteriales genera. With the exception of Zodletone Spring, where the prevalent geochemical conditions are extremely inhospitable to Halobacteriales survival, habitats with fluctuating salinity levels were more diverse than permanently saline habitats. Sequences affiliated with the recently described genera Halogranum, Halolamina, Haloplanus, Halosarcina, and Halorientalis, in addition to the genera Halorubrum, Haloferax, and Halobacterium, were among the most abundant and ubiquitous genera, suggesting a wide distribution of these poorly studied genera in saline sediments. The Halobacteriales sediment communities analyzed in this study were more diverse than and completely distinct from communities from typical hypersaline water bodies. Finally, sequences unaffiliated with currently described genera represented a small fraction of the total Halobacteriales communities, ranging between 2.5% (Zodletone) to 7.0% (mangrove and Great Salt Lake). However, these novel sequences were characterized by remarkably high levels of alpha and beta diversities, suggesting the presence of an enormous, yet-untapped supply of novel Halobacteriales genera within the rare biosphere of various saline ecosystems.

Haloplanus aerogenes sp. nov., an extremely halophilic archaeon from a marine solar saltern

Halophilic archaeal strain TBN37T was isolated from Taibei marine solar saltern near Lianyungang city of Jiangsu province, China. Cells were pleomorphic, flat and contained gas vesicles. Cells of strain TBN37T stained Gram-negative and the colonies were pink-pigmented. The strain was able to grow at 25–50 °C (optimum, 37–40 °C), with 1.4–5.1 M NaCl (optimum, 2.1 M NaCl), with 0–1.0 M MgCl2 (optimum, 0.01 M MgCl2) and at pH 6.0–9.0 (optimum, pH 7.5). Cells lysed in distilled water and the minimal NaCl concentration to prevent cell lysis was 8 % (w/v). The major polar lipids of strain TBN37T were phosphatidylglycerol, phosphatidylglycerol phosphate methyl ester, phosphatidylglycerol sulfate and one major glycolipid chromatographically identical to sulfated mannosyl glucosyl diether (S-DGD-1). On the basis of 16S rRNA gene sequence analysis, strain TBN37T was closely related to Haloplanus natans and Haloplanus vescus, with the same similarity of 97.4 %. The DNA G+C content of strain TBN37T is 64.1 mol%. DNA–DNA hybridization values between strain TBN37T and Haloplanus natans JCM 14081T and between strain TBN37T and Haloplanus vescus RO5-8T were 37.6 % and 42.1 %, respectively. It was concluded that strain TBN37T represents a novel species of the genus Haloplanus, for which the name Haloplanus aerogenes sp. nov. is proposed. The type strain is TBN37T ( = CGMCC 1.10124T  = JCM 16430T).

Halogeometricum rufum sp. nov., a halophilic archaeon from a marine solar saltern, and emended description of the genus Halogeometricum

Two halophilic archaea, strains RO1-4T and RO1-64, were isolated from a marine solar saltern in Jiangsu, China. Cells of the two strains were pleomorphic, motile, and stained Gram-negative. Colonies were red-pigmented. Strains RO1-4T and RO1-64 were able to grow at 25–55 °C (optimum 40–42 °C), at 2.1–5.1 M NaCl (optimum 3.9 M NaCl), at 0.05–0.7 M MgCl2 (optimum 0.3 M MgCl2) and at pH 6.0–8.5 (optimum pH 7.0). Cells lyse in distilled water and the minimal NaCl concentration to prevent cell lysis is 12 % (w/v). On the basis of 16S rRNA gene sequence analysis, strains RO1-4T and RO1-64 were closely related to Halogeometricum borinquense PR3T (98.0 and 98.2 % similarity, respectively) and Halosarcina pallida BZ256T (97.8 and 97.9 %). The major polar lipids of the two strains were phosphatidylglycerol, phosphatidylglycerol phosphate methyl ester and two glycolipids (S-DGD-1 and DGD-1). The DNA G+C contents of strains RO1-4T and RO1-64 are 64.9 and 62.4 mol%, respectively. The DNA–DNA hybridization value between strains RO1-4T and RO1-64 was 83.0 % and both strains showed low DNA–DNA relatedness with Halogeometricum borinquense PR3T (42.5 and 50.1 % relatedness, respectively) and Halosarcina pallida BZ256T (37.6 and 42.1 % relatedness). It was concluded that strains RO1-4T and RO1-64 represent a novel species of the genus Halogeometricum, for which the name Halogeometricum rufum sp. nov. is proposed. The type strain is RO1-4T (=CGMCC 1.7736T =JCM 15770T).

Natronoarchaeum mannanilyticum gen. nov., sp. nov., an aerobic, extremely halophilic archaeon isolated from commercial salt

Strain YSM-123T was isolated from commercial salt made from Japanese seawater in Niigata prefecture. Optimal NaCl and Mg2+ concentrations for growth were 4.0–4.5 M and 5 mM, respectively. The isolate was a mesophilic and slightly alkaliphilic haloarchaeon, whose optimal growth temperature and pH were 37 °C and pH 8.0–9.0. Phylogenetic analysis based on 16S rRNA gene sequence analysis suggested that strain YSM-123T is a member of the phylogenetic group defined by the family Halobacteriaceae, but there were low similarities to type strains of other genera of this family (≤90 %); for example, Halococcus (similarity <89 %), Halostagnicola (<89 %), Natronolimnobius (<89 %), Halobiforma (<90 %), Haloterrigena (<90 %), Halovivax (<90 %), Natrialba (<90 %), Natronobacterium (<90 %) and Natronococcus (<90 %). The G+C content of the DNA was 63 mol%. Polar lipid analysis revealed the presence of phosphatidylglycerol, phosphatidylglycerophosphate methyl ester, disulfated diglycosyl diether and an unknown glycolipid. On the basis of the data presented, we propose that strain YSM-123T should be placed in a new genus and species, Natronoarchaeum mannanilyticum gen. nov., sp. nov. The type strain of Natronoarchaeum mannanilyticum is strain YSM-123T (=JCM 16328T =CECT 7565T).

Halosarcina limi sp. nov., a halophilic archaeon from a marine solar saltern, and emended description of the genus Halosarcina

A halophilic archaeon, strain RO1-6T, was isolated from a marine solar saltern in eastern China. Cells of strain RO1-6T were pleomorphic and motile and stained Gram-negative. Strain RO1-6T grew well on complex medium and colonies were red-pigmented. It was able to grow at 20–50 °C (optimum 37 °C), in 2.1–5.1 M NaCl (optimum 3.9 M NaCl), in 0.05–0.70 M MgCl2 (optimum 0.30 M MgCl2) and at pH 6.5–8.0 (optimum pH 7.0). Cells lysed in distilled water and the minimal NaCl concentration to prevent cell lysis was 12 % (w/v). The major polar lipids of strain RO1-6T were phosphatidylglycerol, phosphatidylglycerol phosphate methyl ester and two glycolipids that were chromatographically identical to S-DGD-1 and S2-DGD. The 16S rRNA gene sequence of strain RO1-6T showed similarities of 96.9 and 96.4 % to those of the type strains of Halosarcina pallida and Halogeometricum borinquense, respectively, members of the most closely related recognized genera within the family Halobacteriaceae. The DNA G+C content of strain RO1-6T was 61.2 mol%. Phenotypic characterization and phylogenetic analysis revealed that strain RO1-6T is related to Halosarcina pallida and represents a novel species of the genus Halosarcina, for which the name Halosarcina limi sp. nov. is proposed; the type strain is RO1-6T (=CGMCC 1.8711T =JCM 16054T).

Metagenomics and recovery of enzyme genes from alkaline saline environments

Enzymes functioning at alkaline pH are widely used in the detergent industry as additives to improve the stain removal properties of domestic and industrial cleaning products. This industry provides by far the major mass market for enzymes. With constantly changing formulations in detergents and concerns over energy demands, new and improved enzymes are constantly in demand. Soda lakes host dense populations of alkali-loving microbes and, as such, provide vast reservoirs of potentially useful enzymes for such an industry. Traditional recovery methods for new enzymes have involved the isolation of microbes, preferably from a compatible chemical environment such as a soda lake, followed by screening of the isolates for useful enzymic activity. At least two commercially significant enzymes originating from soda lake microbes have been marketed following this route. However, the failure to cultivate more than a small percentage of microbes from most environments necessarily markedly reduces the recovery of new enzymes. In recent years, interest has focussed on more comprehensive recovery methods based around detecting appropriate enzyme genes in nucleic acids extracted from potentially useful sites, thus maximizing coverage of the whole genetic resource in a particular biotope. Here we review progress to date in soda lake biotopes and discuss ways the field may develop in the future.

Halolamina pelagica gen. nov., sp. nov., a new member of the family Halobacteriaceae

Two extremely halophilic archaeal strains, TBN21(T) and TBN49, were isolated from the Taibei marine solar saltern near Lianyungang city, Jiangsu province, China. Cells of the two strains were pleomorphic and gram-negative and colonies were red. Strains TBN21(T) and TBN49 were able to grow at 25-50 °C (optimum 37 °C), at 1.4-5.1 M NaCl (optimum 3.4-3.9 M) and at pH 5.5-9.5 (optimum pH 7.0-7.5) and neither strain required Mg(2+) for growth. Cells lysed in distilled water and the minimal NaCl concentration to prevent cell lysis was 8 % (w/v). The major polar lipids of the two strains were phosphatidic acid, phosphatidylglycerol, phosphatidylglycerol phosphate methyl ester, phosphatidylglycerol sulfate and eight glycolipids; three of these glycolipids (GL3, GL4 and GL5) were chromatographically identical to sulfated mannosyl glucosyl diether (S-DGD-1), galactosyl mannosyl glucosyl diether (TGD-1) and mannosyl glucosyl diether (DGD-1), respectively. Phylogenetic analysis revealed that strains TBN21(T) and TBN49 formed a distinct clade with their closest relative, Halobaculum gomorrense JCM 9908(T) (89.0-89.5 % 16S rRNA gene sequence similarity). The DNA G+C contents of strains TBN21(T) and TBN49 were 64.8 and 62.7 mol%, respectively. DNA-DNA hybridization between strains TBN21(T) and TBN49 was 90.1 %. The phenotypic, chemotaxonomic and phylogenetic properties suggest that strains TBN21(T) and TBN49 represent a novel species in a new genus within the family Halobacteriaceae, for which the name Halolamina pelagica gen. nov., sp. nov. is proposed. The type strain of Halolamina pelagica is TBN21(T) ( = CGMCC 1.10329(T)  = JCM 16809(T)).

Haloplanus vescus sp. nov., an extremely halophilic archaeon from a marine solar saltern, and emended description of the genus Haloplanus

An extremely halophilic archaeon, strain RO5-8T, was isolated from a disused marine solar saltern in China. The cells were pleomorphic and flat. In static liquid medium, cells floated to the surface. Strain RO5-8Tstained Gram-negative and colonies were pink-pigmented. It was able to grow at 30–50 °C (optimum 40 °C), at 2.6–4.3 M NaCl (optimum 3.1 M NaCl), at 0.03–0.5 M MgCl2(optimum 0.03 M MgCl2) and at pH 5.5–7.5 (optimum pH 6.0–6.5). Cells lysed in distilled water and the minimal NaCl concentration to prevent cell lysis was 12 % (w/v). The major polar lipids of strain RO5-8Twere phosphatidylglycerol, phosphatidylglycerol phosphate methyl ester, phosphatidylglycerol sulfate and one major glycolipid chromatographically identical to the sulfated mannosyl glucosyl diether S-DGD-1. On the basis of 16S rRNA gene sequence analysis, strain RO5-8Twas closely related to three strains ofHaloplanus natanswith similarities of 97.3–97.6 %. The DNA G+C content of strain RO5-8Twas 62.1 mol%. The DNA–DNA hybridization value between strain RO5-8TandHaloplanus natansJCM 14081Twas 51.6 %. It was concluded that strain RO5-8Trepresents a novel species of the genusHaloplanus, for which the nameHaloplanus vescussp. nov. is proposed. The type strain is RO5-8T(=CGMCC 1.8712T=JCM 16055T).

Halopelagius inordinatus gen. nov., sp. nov., a new member of the family Halobacteriaceae isolated from a marine solar saltern

Two extremely halophilic archaea, strains RO5-2(T) and RO5-14, were isolated from Rudong marine solar saltern in Jiangsu, China. Cells of the two strains were pleomorphic, motile and stained Gram-negative. Colonies were red-pigmented. Strains RO5-2(T) and RO5-14 were able to grow at 20-50 degrees C (optimum 37 degrees C), at 2.6-4.8 M NaCl (optimum 3.4-3.9 M NaCl), at 0.03-0.7 M MgCl(2) (optimum 0.5 M MgCl(2)) and at pH 5.5-8.0 (optimum pH 6.5-7.0). Cells lyse in distilled water and the minimal NaCl concentration to prevent cell lysis was 12 % (w/v). The major polar lipids of the two strains were phosphatidylglycerol, phosphatidylglycerol phosphate methyl ester and two major glycolipids chromatographically identical to sulfated mannosyl glucosyl diether (S-DGD-1) and mannosyl glucosyl diether (DGD-1). The 16S rRNA gene sequences of strains RO5-2(T) and RO5-14 showed 93.4-93.8 % similarity to the closest cultivated relative, Halosarcina pallida. The DNA G+C content of strains RO5-2(T) and RO5-14 was 61.0 mol% and 59.9 mol%, respectively. The DNA-DNA relatedness between strains RO5-2(T) and RO5-14 was 86.0 %. The phenotypic, chemotaxonomic and phylogenetic properties suggest that strains RO5-2(T) and RO5-14 represent a novel species in a new genus within the family Halobacteriaceae, for which the name Halopelagius inordinatus gen. nov., sp. nov. is proposed. The type strain is RO5-2(T) (=CGMCC 1.7739(T) =JCM 15773(T)).

Natronorubrum sediminis sp. nov., an archaeon isolated from a saline lake

Two novel haloalkaliphilic archaea, strains CG-6T and CG-4, were isolated from sediment of the hypersaline Lake Chagannor in Inner Mongolia, China. Cells of the two strains were pleomorphic, non-motile and strictly aerobic. They required at least 2.5 M NaCl for growth, with optimum growth at 3.4 M NaCl. They grew at pH 8.0-11.0, with optimum growth at pH 9.0. Hypotonic treatment with less than 1.5 M NaCl caused cell lysis. The two strains had similar polar lipid compositions, possessing C20C20 and C20C25 derivatives of phosphatidylglycerol and phosphatidylglycerol phosphate methyl ester. No glycolipids were detected. Comparison of 16S rRNA gene sequences and morphological features placed them in the genus Natronorubrum. 16S rRNA gene sequence similarities to strains of recognized species of the genus Natronorubrum were 96.2-93.8%. Detailed phenotypic characterization and DNA-DNA hybridization studies revealed that the two strains belong to a novel species in the genus Natronorubrum, for which the name Natronorubrum sediminis sp. nov. is proposed; the type strain is CG-6T (=CECT 7487T =CGMCC 1.8981T =JCM 15982T).

Halogranum rubrum gen. nov., sp. nov., a halophilic archaeon isolated from a marine solar saltern

Two extremely halophilic archaea, strains RO2-11(T) and HO2-1, were isolated from two Chinese marine solar salterns, Rudong solar saltern and Haimen solar saltern, respectively. Cells of the two strains were polymorphic and Gram-stain-negative; colonies were red-pigmented. The two strains grew at NaCl concentrations of 2.6-4.3 M (optimum 3.9 M) and required at least 0.1 M Mg2+ for growth. They were able to grow over a pH range of 6.0-8.0 and a temperature range of 20-50 degrees C, with optimal pH of 7.5 and optimal temperature of 37 degrees C. The major polar lipids of strain RO2-11(T) and strain HO2-1 were phosphatidylglycerol, phosphatidylglycerol phosphate methyl ester and three glycolipids, two of them chromatographically identical to S-DGD-1 and DGD-1, the third unidentified. The 16S rRNA gene sequence similarity of strain RO2-11(T) and strain HO2-1 was 99.3 % and highest sequence similarity with the closest relative (Haloferax larsenii) was 91.4 %. Based on the data obtained, the two isolates could not be classified in any recognized genus of the family Halobacteriaceae. Strain RO2-11(T) and strain HO2-1 are thus considered to represent a novel species of a new genus within the family Halobacteriaceae, for which the name Halogranum rubrum gen. nov., sp. nov. is proposed. The type strain is RO2-11(T) (=CGMCC 1.7738(T) =JCM 15772(T)).

Haladaptatus litoreus sp. nov., an extremely halophilic archaeon from a marine solar saltern, and emended description of the genus Haladaptatus

Two extremely halophilic archaea, strains RO1-28(T) and RO1-22, were isolated from a marine solar saltern in Jiangsu, China. Both strains required at least 0.05 M Mg(2+) and 1.7 M NaCl for growth. They were able to grow over a pH range of 6.0-8.5 and a temperature range of 25-55 degrees C, with optimal pH of 7.0 and optimal temperature of 37-40 degrees C. Based on 16S rRNA gene sequence analysis, strains RO1-28(T) and RO1-22 were closely related to Haladaptatus paucihalophilus, the single species of the genus Haladaptatus, with similarities of 94.0-95.2 %. The major polar lipids of the two strains were phosphatidylglycerol, phosphatidylglycerol phosphate methyl ester, phosphatidylglycerol sulfate and three glycolipids chromatographically identical to the glycolipids of Haladaptatus paucihalophilus JCM 13897(T). Both strains RO1-28(T) and RO1-22 had a DNA G+C content of 54.0 mol% (HPLC). The DNA-DNA hybridization value between the two strains was more than 70 % (92 %) and both strains showed low levels of DNA-DNA relatedness (32 % and 33 %) with Haladaptatus paucihalophilus JCM 13897(T). It was concluded that strains RO1-28(T) and RO1-22 represent a novel species of the genus Haladaptatus, for which the name Haladaptatus litoreus sp. nov. is proposed. The type strain is RO1-28(T) (=CGMCC 1.7737(T) =JCM 15771(T)).

Haloterrigena salina sp. nov., an extremely halophilic archaeon isolated from a salt lake

A novel extremely halophilic strain, designated XH-65(T), isolated from the salt lake Xilinhot in Inner Mongolia, PR China, was subjected to a polyphasic taxonomic characterization. Strain XH-65(T) is neutrophilic, non-motile and requires at least 2.5 M NaCl for growth, with an optimum at 3.4 M NaCl, and grows at pH 6.0-9.0, with optimum growth at pH 7.5. Strain XH-65(T) grows at 25-50 degrees C, with optimal growth at 37 degrees C. Magnesium is not required for growth. On the basis of 16S rRNA gene sequence analysis, strain XH-65(T) was shown to belong to the genus Haloterrigena and was related to Haloterrigena turkmenica VKM B-1734(T) (98.1 % sequence similarity), Haloterrigena saccharevitans AB14(T) (96.9 %), Haloterrigena thermotolerans PR5(T) (96.3 %), Haloterrigena limicola AX-7(T) (95.8 %) and Haloterrigena hispanica FP1(T) (95.7 %). DNA-DNA hybridization revealed 37 % relatedness between strain XH-65(T) and Htg. turkmenica VKM B-1734(T). The polar lipid composition revealed the presence of phosphatidylglycerol, phosphatidylglycerol phosphate methyl ester and mannose-2,6-disulfate (1-->2)-glucose glycerol diether (S(2)-DGD). The results of the DNA-DNA hybridization and physiological and biochemical tests allowed genotypic and phenotypic differentiation of strain XH-65(T) from the six Haloterrigena species with validly published names. Therefore, strain XH-65(T) represents a novel species, for which the name Haloterrigena salina sp. nov. is proposed, with the type strain XH-65(T) (=CGMCC 1.6203(T) =JCM 13891(T)).

Halophilic archaea isolated from man-made young (200 years) salt lakes in Slănic, Prahova, Romania

We isolated a number of extremely halophilic archaea from four salt lakes (Red Bath, Green Bath, Shepherd Bath and Bride Cave) located in Slanic Prahova, Romania. The characterization of 12 representative isolates by polyphasic approach revealed that 11 strains were members of the genus Haloferax and only one was a member of the genus Haloarcula. The 11 Haloferax isolates possessed sulfated diglycosylarchaeol-1 as the major membrane glycolipid, and G+C contents of total DNA were 63.4–65.8 mol%. The predominant isolation of Haloferax species from the lakes may suggest that the underground salt deposit possesses Haloferax species as the major biota of ancient origin. To the best of the authors’ knowledge, this is the first paper on the survey of halophilic archaea of man-made young salt lakes.

Halomicrobium katesii sp. nov., an extremely halophilic archaeon

Two extremely halophilic archaea, strains Al-5(T) and K-1, were isolated from Lake Tebenquiche (Atacama Saltern, Chile) and Ezzemoul sabkha (Algeria), respectively. Cells of the two strains were short-rod-shaped and Gram-negative; colonies were orange-pigmented. They grew optimally at 37-40 degrees C and pH 7.0-7.5 in the presence of 25 % (w/v) NaCl. Magnesium was not required. Polar lipid analysis revealed the presence of phosphatidylglycerol and phosphatidylglycerophosphate methyl ester, the absence of phosphatidylglycerosulfate, and the presence of sulfated diglycosyl diether and diether diglycosyl as the sole glycolipids. DNA G+C contents of strains Al-5(T) and K-1 were 52.4 and 52.9 mol% (T(m) method), respectively. 16S rRNA gene sequence comparison with database sequences showed that strains Al-5(T) and K-1 were most closely related to Halomicrobium mukohataei DSM 12286(T) (similarities of 97.5 and 96.9 %, respectively). DNA-DNA hybridization indicated that strains Al-5(T) and K-1 were members of a single species. However, DNA-DNA relatedness to Halomicrobium mukohataei was 55.7+/-2.5 %. A comparative analysis of phenotypic characteristics and DNA-DNA hybridization between the isolates and Halomicrobium mukohataei DSM 12286(T) supported the conclusion that Al-5(T) and K-1 represent a novel species within the genus Halomicrobium, for which the name Halomicrobium katesii sp. nov. is proposed. The type strain is Al-5(T) (=CECT 7257(T)=DSM 19301(T)).