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At least 19 recordsLinked to original sources
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↗
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↗
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↗
PubMed1995

Life in unusual environments: progress in understanding the structure and function of enzymes from extreme halophilic bacteria.

Extreme halophilic archaea are saturated with salt and the intracellular electrolyte concentration exceeds that of the extracellular environment. Enzymes and other proteins from extreme halophilic archaea have been purified for many years and studied by biochemical and biophysical solution methodologies. They are active and stable at multimolar salt concentrations and denature below 2 to 3 M NaCl or KCl. Adaptation to these high concentrations of salt, genetic and evolutionary aspects, and the possibility of biotechnological applications are problems of considerable interest. Since the status of this fascinating field of research was reviewed in 1992, malate dehydrogenase from Haloarcula marismortui, now known to be a tetramer, was sequenced, its gene was cloned and expressed in active form, and its physical properties were redefined. A single mutation of Arg100 (in the enzyme active site) to Gln switched the enzyme specificity from malate to lactate dehydrogenase. Recent determination of its molecular structure by X-ray crystallography (O. Dym et al., in press) provides an exciting basis for the understanding of the structure and function of extreme halophilic enzymes. A major problem which so far has not been tackled in the study of extreme halophilic archaea is the understanding of protein nucleic acid interactions which are essential for the performance of biological function. Whereas the stability and activity of enzymes and other proteins can be modified to perform at high salt concentrations by use of currently known structural concepts, the existence of meaningful protein nucleic acid interactions in physiological concentrations of 4 to 5 M KCl constitutes an unsolved enigma worth intensive investigation.

Environment↗
PubMed1993

A protein-serine phosphatase from the halophilic archaeon Haloferax volcanii.

We have detected a protein phosphatase activity in soluble extracts from the halophilic archaeon Haloferax volcanii. This activity was markedly stimulated by the divalent metal ions Mn2+ and Cd2+. It dephosphorylated phosphoseryl residues in casein, mixed histones, and phosphorylase a, but not phosphotyrosyl residues in reduced, carboxyamidomethylated and maleylated lysozyme. This protein phosphatase activity was inhibited by NaF, Zn2+, vanadate, molybdate, inorganic phosphate, inorganic pyrophosphate, or p-nitrophenyl phosphate, or by treatment with diethylpyrocarbonate. Activity was unaffected by other potential inhibitors or activators such as polyamines, heparin, cyclic nucleotides, Ca2+/calmodulin, tartrate, tetramisole, okadaic acid, microcystin LR, or sulfhydryl-modifying agents. The functional similarities between this protein-serine phosphatase and that previously identified in another archaeon, the extreme acidothermophile Sulfolobus solfataricus, suggest the existence of a family of divalent metal ion-stimulated protein-serine phosphatases of extremely ancient origin in the Archaea.

Cadmium↗
PubMed1993

Localization of proteins HL29 and HL31 from Haloarcula marismortui within the 50 S ribosomal subunit by chemical crosslinking.

Isolated 50 S ribosomal subunits from the halophilic archaebacterium Haloarcula marismortui were treated in situ with the homobifunctional and cleavable crosslinking reagent dithiobis(succinimidyl propionate) (12 A). Several crosslinked complexes were obtained. Among these were the protein pairs HmaL4-HL29 and HmaL18-HL31; HL29 and HL31 are ribosomal proteins without any equivalent in eubacterial ribosomes. The crosslinked protein pairs were isolated on a preparative scale by combining conventional ion-exchange chromatography and reverse phase high-pressure liquid chromatography. The monomeric proteins involved in crosslink formation were unambiguously identified by two-dimensional gel electrophoresis and N-terminal or internal protein sequencing. Due to the homology between HmaL4 and HmaL18 and their Escherichia coli counterparts, and the roughly known location of these proteins within the 50 S subunit, our results demonstrate that HL29 is probably located in the centre of the large subunit in the vicinity of the peptidyltransferase domain, whereas HL31 must be situated within the central protuberance close to the region of the 5 S RNA.

Amino Acid Sequence↗
PubMed1993

HF1 and HF2: novel bacteriophages of halophilic archaea.

Two novel halophilic archaebacterial bacteriophages, HF1 and HF2, were isolated from an Australian solar saltern. They were morphologically identical with icosahedral-shaped heads (diameter 58 nm) and contractile tails (length 94 nm). Other similarities included sensitivity to reduced ionic conditions, similar protein profiles by SDS-PAGE, and dsDNA genomes of identical size (73.5 kbp) with analogous restriction patterns. DNA-DNA hybridization data showed the two phages to be closely related. HF1 has a broad host-range, infecting members of three halobacterial genera including Halobacterium salinarium and the genetically well-characterized strain Haloferax volcanii WFD11. Mutants showing increased plating efficiency on alternative hosts were readily selectable. By contrast, HF2 showed a limited host range, confined to the closely related dam-methylated strains Ch2 and H. saccharovorum.

Bacteriophages↗
PubMed1997

Gas vesicle formation in halophilic Archaea.

Gas vesicles are intracellular, microbial flotation devices that consist of mainly one protein, GvpA. The formation of halobacterial gas vesicles occurs along a complex pathway involving 14 different gvp genes that are clustered in a genomic region termed the "vac region". Various vac regions found in Halobacterium salinarum (p-vac and c-vac), Haloferax mediterranei (mc-vac), and Natronobacterium vacuolatum (nv-vac) have been investigated. Except for the latter vac region, the arrangement of the gvp genes is identical. Single gvp genes have been mutated to study the effect on gas vesicle synthesis in transformants and to determine their possible function. Each vac region exhibits a characteristic transcription pattern, and regulatory steps have been observed at the DNA, RNA, and protein level, indicating a complex regulatory network acting during gas vesicle gene expression.

Archaeal Proteins↗
PubMed1991

Glucose transport of Haloferax volcanii requires the Na(+)-electrochemical potential gradient and inhibitors for the mammalian glucose transporter inhibit the transport.

The uptake of glucose and its non-metabolizing analogues by Haloferax volcanii, one of the glucose-utilizing Halobacteria, was examined using intact cells and envelope vesicles. Results obtained were: (1) The transport system is inducible. (2) The uptake requires the gradient of Na(+)-electrochemical potential. (3) Inhibitors for mammalian glucose transport also have an effect on this system, implying that the transporters resemble each other. (4) It is suggested that the mobility of the transporter is regulated by the membrane energization.

Biological Transport, Active↗
PubMed1995

Reason for the lack of light-dark adaptation in pharaonis phoborhodopsin: reconstitution with 13-cis-retinal.

The reconstitution of pharaonis phoborhodopsin was performed by incubation of its opsin with 13-cis-retinal. Spectrum change was very slow, and two phases of the change were observed: the first and second phases are due to the transient formation of 13-cis pigment and spontaneous isomerization to all-trans-retinal, respectively. Slow binding supports an idea that the retinal binding pocket of ppR is highly restricted. Being bent in the configuration, 13-cis-retinal cannot be accommodated in the pocket due to the steric hindrance. This is a possible reason for the lack of light-dark adaptation.

Archaeal Proteins↗
PubMed1996

Evidence for farnesol-mediated isoprenoid synthesis regulation in a halophilic archaeon, Haloferax volcanii.

Farnesol strongly inhibited growth of a halophilic archaeon, Haloferax volcanii, with an IC50 value of only 2 microM (0.4 microgram/ml) in rich medium and 50 nM (0.01 microgram/ml) in minimal medium without lysis. Other isoprenoid alcohols such as isopentenol, dimethylallyl alcohol, geraniol, and geranylgeraniol at 500 microM did not affect its growth. Mevalonate, which is the precursor of all isoprenoid membrane lipids in archaea, led to recovery of the growth inhibition of H. volcanii, but acetate had no such effect. Farnesol inhibited incorporation of acetate, but not mevalonate, into the lipid fraction. These results suggest that farnesol inhibited the biosynthetic pathway from acetate (acetyl-CoA) to mevalonate. Farnesol is known to be derived from the important intermediate of isoprenoids, farnesyl diphosphate (FPP), and found in neutral lipid fraction from this archaeon. Moreover, the cell-free extracts from H. volcanii could phosphorylate farnesol with ATP to generate farnesyl monophosphate and FPP. We conclude that farnesol-mediated isoprenoid synthesis regulation system by controlling farnesol concentration is present in H. volcanii.

Acetates↗
PubMed1994

Characterization of 1-phosphofructokinase from halophilic archaebacterium Haloarcula vallismortis.

1-Phosphofructokinase (EC 2.7.1.56) (1PFK) was purified and characterized for the first time from an archaebacterial halophile Haloarcula vallismortis. The purification procedure involving (NH4)2SO4 fractionation, (NH4)2SO4-mediated chromatography on Sepharose 4B, CM-cellulose chromatography, hydrophobic chromatography on phenyl Sepharose and adsorption chromatography on hydroxylapatite yielded a preparation with a specific activity of 128 and 100-fold purification. From gel filtration and sucrose density gradient ultracentrifugation, the apparent molecular mass of halobacterial 1PFK was found as 76 +/- 5 kDa. The halobacterial 1PFK appears to be monomeric and the possibility of an unstable phosphoenzyme intermediate during its catalysis could not be ruled out. As in the case of many halobacterial enzymes, the 1PFK was found to be halophilic and thermostable. Other catalytic features of halobacterial 1PFK were similar to its counterparts from eubacterial sources.

Enzyme Stability↗
PubMed1996

The repair of ultraviolet light-induced DNA damage in the halophilic archaebacteria, Halobacterium cutirubrum, Halobacterium halobium and Haloferax volcanii.

Extremely halophilic archaebacteria have been reported to have no capacity for dark repair (excision repair) of ultraviolet damage and to rely on very efficient photoreactivation for recovery after UVC irradiation. Post-UV incubation in the light restores 100% survival in these organisms. This has been taken to indicate that cyclobutane dimers are the only significant UV-induced lesions and that they are completely repaired by photoreactivation. However, in all organisms studied to date, pyrimidine (6-4) pyrimidone photoproducts are a significant cytotoxic and mutagenic lesion and constitute 10-30% of UV photoproducts. The question arises, therefore--are 6-4 photoproducts induced in the halophilic archaebacteria and, if they are, how are they repaired? This paper shows that both cyclobutane dimers and 6-4 photoproducts are induced in the extremely halophilic archaebacteria, Halobacterium cutirubrum, Halobacterium halobium and Haloferax volcanii, at similar levels as in other organisms. Furthermore, contrary to previous reports, there is dark repair of both lesions. As in other organisms, 6-4 photoproducts are removed more efficiently than cyclobutane dimers in the dark. In the light, cyclobutane dimers are repaired very rapidly and there is also photoenhanced repair of 6-4 photoproducts. This work confirms that organisms such as Halobacterium and Haloferax which live in conditions of high exposure to sunlight have very efficient rates of repair of UV lesions in the light.

DNA Damage↗
PubMed1993

Halophilic class I aldolase and glyceraldehyde-3-phosphate dehydrogenase: some salt-dependent structural features.

Aldolase and glyceraldehyde-3-phosphate dehydrogenase from the extremely halophilic archaebacterium Haloarcula vallismortis are stable only in high concentrations of KCl present within the physiological environment. Data concerning the structural changes in the two enzymes as a result of lowering of salt concentration and changes in pH were obtained by monitoring the intrinsic protein fluorescence in the presence of quenchers. When the KCl concentrations were lowered below 2 M or in the presence of 6 M guanidine hydrochloride, the emission maximum shifted to a longer wavelength, indicating enhanced exposure of tryptophyl residues to the solvent. The spectral characteristics of the two proteins in guanidine hydrochloride and 0.4 M KCl were identical. However, these denatured states appear to be different than those observed after acid denaturation. Further perturbation of fluorescence was observed due to I-, and application of the Stern-Volmer law showed that the total fluorescence was available to the quenchers only in 0.4 M KCl solutions. The unfolding of proteins in 0.4 M KCl was a gradual process which was accompanied by a time-dependent loss in enzyme activity. The activity loss was complete within 30 min for aldolase whereas in the case of GAPDH nearly 3 h was required for the destruction of activity. For both enzymes, inactivation and protein denaturation were strongly correlated. The data on activity and thermostability measurements of the two enzymes in varying concentrations of KCl and potassium phosphate revealed that though both proteins are halophilic, the forces in the maintenance of their stability could be different.(ABSTRACT TRUNCATED AT 250 WORDS)

Acrylamide↗
PubMed1997

Construction and analysis of a recombination-deficient (radA) mutant of Haloferax volcanii.

By deleting the radA open reading frame of an extreme halophile, Haloferax volcanii, we created and characterized a recombination-deficient archaeon. This strain, Hf. volcanii DS52, has no detectable DNA recombination, is more sensitive to DNA damage by UV light and ethylmethane sulfonate, and has a slower growth rate than the wild type. These characteristics are similar to those observed in recombination mutants of Eukarya and Bacteria, and show that the radA gene belongs in the recA/RAD51 family by function as well as sequence homology. In addition, strain DS52 was not transformable by plasmids pWL102 or pUBP2 (which contain pHV2 and pHH1 replicons, respectively), although it was readily transformed by plasmids containing a pHK2 replicon, indicating a role for radA in the maintenance or replication of some halobacterial plasmids. Despite its slower growth rate, Hf. volcanii DS52 was still easy to culture and transform, and should be suitable for use in studies where a recombination-deficient background is desired.

Archaeal Proteins↗