Halobacterium yunchengense sp. nov., Natronomonas amylolytica sp. nov., Halorientalis halophila sp. nov., Halobellus salinisoli sp. nov., halophilic archaea isolated from a saline lake and inland saline soil.

Four halophilic archaeal strains YCN1T, YCN58T, LT38T, and LT62T were isolated from Yuncheng Salt Lake (Shanxi, China) and Tarim Basin (Xinjiang, China), respectively. Phylogenetic and phylogenomic analyses showed that these four strains tightly cluster with related species of Halobacterium, Natronomonas, Halorientalis, and Halobellus, respectively. The AAI, ANI, and dDDH values between these four strains and their related species of respective genera were lower than the proposed threshold values for species delineation. Strains YCN1T, YCN58T, LT38T, and LT62T could be differentiated from the current species of Halobacterium, Natronomonas, Halorientalis, and Halobellus, respectively, based on the comparison of diverse phenotypic characteristics. The polar lipid profiles of these four strains were closely similar to those of respective relatives within the genera Halobacterium, Natronomonas, Halorientalis, and Halobellus, respectively. The phenotypic, phylogenetic, and genome-based analyses indicated that strains YCN1T, YCN58T, LT38T, and LT62T represent respective novel species within the genera Halobacterium, Natronomonas, Halorentalis, and Halobellus, for which the names Halobacterium yunchengense sp. nov., Natronomonas amylolytica sp. nov., Halorientalis halophila sp. nov., and Halobellus salinisoli sp. nov. are proposed, respectively.

Halobacterium bonnevillei sp. nov., Halobaculum saliterrae sp. nov. and Halovenus carboxidivorans sp. nov., three novel carbon monoxide-oxidizing Halobacteria from saline crusts and soils.

Three novel carbon monoxide-oxidizing Halobacteria were isolated from Bonneville Salt Flats (Utah, USA) salt crusts and nearby saline soils. Phylogenetic analysis of 16S rRNA gene sequences revealed that strains PCN9T, WSA2T and WSH3T belong to the genera Halobacterium, Halobaculum and Halovenus, respectively. Strains PCN9T, WSA2T and WSH3T grew optimally at 40 °C (PCN9T) or 50 °C (WSA2T, WSH3T). NaCl optima were 3 M (PCN9T, WSA2T) or 4 M NaCl (WSH3T). Carbon monoxide was oxidized by all isolates, each of which contained a molybdenum-dependent CO dehydrogenase. G+C contents for the three respective isolates were 66.75, 67.62, and 63.97 mol% as derived from genome analyses. The closest phylogenetic relatives for PCN9T, WSA2T and WSH3T were Halobacterium noricense A1T, Halobaculum roseum D90T and Halovenus aranensis EB27T with 98.71, 98.19 and 95.95 % 16S rRNA gene sequence similarities, respectively. Genome comparisons of PCN9T with Halobacterium noricense A1T yielded an average nucleotide identity (ANI) of 82.0% and a digital DNA-DNA hybridization (dDDH) value of 25.7 %; comparisons of WSA2T with Halobaculum roseum D90T yielded ANI and dDDH values of 86.34 and 31.1 %, respectively. The ANI value for a comparison of WSH3T with Halovenus aranensis EB27T was 75.2 %. Physiological, biochemical, genetic and genomic characteristics of PCN9T, WSA2T and WSH3T differentiated them from their closest phylogenetic neighbours and indicated that they represent novel species for which the names Halobaculum bonnevillei, Halobaculum saliterrae and Halovenus carboxidivorans are proposed, respectively. The type strains are PCN9T (=JCM 32472=LMG 31022=ATCC TSD-126), WSA2T (=JCM 32473=ATCC TSD-127) and WSH3T (=JCM 32474=ATCC TSD-128).

Halobacterium litoreum sp. nov., isolated from a marine solar saltern.

Halophilic archaeal strain ZS-54-S2T was isolated from Zhoushan marine solar saltern, China. Cells were rod-shaped, Gram-stain-negative and formed red-pigmented colonies on an agar plate. Strain ZS-54-S2T was able to grow at 20-50 °C (optimum 35 °C), at 1.7-4.8 M NaCl (optimum 3.9 M), at 0.005-1.0 M MgCl2 (optimum 0.05 M) and at pH 5.0-9.5 (optimum pH 7.0). The cells lysed in distilled water and the minimal NaCl concentration to prevent cell lysis was found to be 5 % (w/v). The major polar lipids of the strain were phosphatidic acid, phosphatidylglycerol, phosphatidylglycerol phosphate methyl ester, two glycolipids, which were chromatographically identical to sulfated galactosyl mannosyl galactofuranosyl glucosyl diether and galactosyl mannosyl glucosyl diether, and an unidentified glycolipid, which was chromatographically identical to one detected in Halobacterium salinarum ATCC 33171T. The 16S rRNA gene and rpoB' gene of strain ZS-54-S2T were phylogenetically related to the corresponding genes of Halobacterium noricense JCM 15102T (97.5 % and 90.6 % relatedness, respectively), Halobacterium jilantaiense CGMCC 1.5337T (96.9 and 91.2 %), Halobacterium rubrum CGMCC 1.12575T (96.8 and 90.3 %) and Halobacterium salinarum CGMCC 1.1958T (96.5 and 88.4 %). The DNA G+C content of strain ZS-54-S2T was 66.7 mol%. The phenotypic, chemotaxonomic and phylogenetic properties suggested that strain ZS-54-S2T (=CGMCC 1.12562T=JCM 30038T) represents a new species of Halobacterium, for which the name Halobacteriumlitoreum sp. nov. is proposed.

Genomic Analysis of the Extremely Halophilic Archaeon Halobacterium noricense CBA1132 Isolated from Solar Salt That Is an Essential Material for Fermented Foods.

The extremely halophilic archaeon Halobacterium noricense is a member of the genus Halobacterium. Strain CBA1132 (= KCCM 43183, JCM 31150) was isolated from solar salt. The genome of strain CBA1132 assembled with 4 contigs, including three rRNA genes, 44 tRNA genes, and 3,208 open reading frames. Strain CBA1132 had nine putative CRISPRs and the genome contained genes encoding metal resistance determinants: copper-translocating P-type ATPase (CtpA), arsenical pump-driving ATPase (ArsA), arsenate reductase (ArsC), and arsenical resistance operon repressor (ArsR). Strain CBA1132 was related to Halobacterium noricense, with 99.2% 16S rRNA gene sequence similarity. Based on the comparative genomic analysis, strain CBA1132 has distinctly evolved; moreover, essential genes related to nitrogen metabolism were only detected in the genome of strain CBA1132 among the reported genomes in the genus Halobacterium. This genome sequence of Halobacterium noricense CBA1132 may be of use in future molecular biological studies.

The complete genome of a viable archaeum isolated from 123-million-year-old rock salt.

Live microbes have been isolated from rock salt up to Permian age. Only obligatory cellular functions can be performed in halite-buried cells. Consequently, their genomic sequences are likely to remain virtually unchanged. However, the available sequence information from these organisms is scarce and consists of mainly ribosomal 16S sequences. Here, live archaea were isolated from early Cretaceous (∼ 123 million years old) halite from the depth of 2000 m in Qianjiang Depression, Hubei Province, China. The sample was radiologically dated and subjected to rigorous surface sterilization before microbe isolation. The isolates represented a single novel species of Halobacterium, for which we suggest the name Halobacterium hubeiense, type strain Hbt. hubeiense JI20-1. The species was closely related to a Permian (225-280 million years old) isolate, Halobacterium noricense, originating from Alpine rock salt. This study is the first one to publish the complete genome of an organism originating from surface-sterilized ancient halite. In the future, genomic data from halite-buried microbes can become a key factor in understanding the mechanisms by which these organisms are able to survive in harsh conditions deep underground or possibly on other celestial bodies.

Purification and characterization of halo-alkali-thermophilic protease from Halobacterium sp. strain HP25 isolated from raw salt, Lake Qarun, Fayoum, Egypt.

A total of 33 halophilic protease producers were isolated from different salt samples collected from Emisal salt company at Lake Qarun, Fayoum, Egypt. Of these strains, an extremely halophilic strain that grew optimally at 30 % (w/v) NaCl was characterized and identified as Halobacterium sp. strain HP25 based on 16S rRNA gene sequencing and phenotypic characterization. A halo-alkali-thermophilic protease was purified in three successive steps from the culture supernatant. The purified halophilic protease consisted of a single polypeptide chain with a molecular mass of 21 kDa and was enriched 167-fold to a specific activity of 6350 U mg(-1). The purified enzyme was active over a broad pH range from 6.0 to 11.0, with maximum activity at pH 8.0, exhibited a broad temperature range from 30 to 80 °C with optimum activity at 60 °C, and was active at salt concentrations ranging from 5 to 25 % (w/v), with optimum activity at 17 % NaCl (w/v). The K M and V max values of the purified halophilic protease with casein as a substrate were 523 µg mL(-1) and 2500 µg min(-1) mL(-1), respectively. In addition, this enzyme was stable in the tested organic solvents and laundry detergents such methanol, propanol, butanol, hexane, Persil and Ariel. The unusual properties of this enzyme allow it to be used for various applications, such as the ripening of salted fish. Furthermore, its stability and activity in the presence of organic solvents and detergents also allow the use of this enzyme for further novel applications and as an additive in detergent formulations.

Halophilic microorganisms are responsible for the rosy discolouration of saline environments in three historical buildings with mural paintings.

A number of mural paintings and building materials from monuments located in central and south Europe are characterized by the presence of an intriguing rosy discolouration phenomenon. Although some similarities were observed among the bacterial and archaeal microbiota detected in these monuments, their origin and nature is still unknown. In order to get a complete overview of this biodeterioration process, we investigated the microbial communities in saline environments causing the rosy discolouration of mural paintings in three Austrian historical buildings using a combination of culture-dependent and -independent techniques as well as microscopic techniques. The bacterial communities were dominated by halophilic members of Actinobacteria, mainly of the genus Rubrobacter. Representatives of the Archaea were also detected with the predominating genera Halobacterium, Halococcus and Halalkalicoccus. Furthermore, halophilic bacterial strains, mainly of the phylum Firmicutes, could be retrieved from two monuments using special culture media. Inoculation of building materials (limestone and gypsum plaster) with selected isolates reproduced the unaesthetic rosy effect and biodeterioration in the laboratory.

Halobacterium rubrum sp. nov., isolated from a marine solar saltern.

Halophilic archaeal strain TGN-42-S1(T) was isolated from the Tanggu marine solar saltern, China. Cells from strain TGN-42-S1(T) were observed to be pleomorphic rods, stained Gram-negative, and formed red-pigmented colonies on solid media. Strain TGN-42-S1(T) was found to be able to grow at 20-50 °C (optimum 35-37 °C), at 1.7-4.8 M NaCl (optimum 3.1 M), at 0-1.0 M MgCl2 (optimum 0.1 M), and at pH 5.0-9.0 (optimum pH 7.0-7.5). The cells lysed in distilled water, and the minimal NaCl concentration to prevent cell-lysis was found to be 10 % (w/v). The major polar lipids of the strain were phosphatidic acid, phosphatidylglycerol, phosphatidylglycerol phosphate methyl ester, phosphatidylglycerol sulfate, galactosyl mannosyl glucosyl diether (TGD-1), sulfated galactosyl mannosyl glucosyl diether (S-TGD-1), sulfated galactosyl mannosyl galactofuranosyl glucosyl diether (S-TeGD), and three unidentified glycolipids which were chromatographically identical to those of the Halobacterium species. The 16S rRNA gene and rpoB' gene of strain TGN-42-S1(T) were phylogenetically related to the corresponding genes of Halobacterium jilantaiense CGMCC 1.5337(T) (98.8 and 93.5 % nucleotide identity, respectively), Halobacterium salinarum CGMCC 1.1958(T) (98.4 and 91.9 %), and Halobacterium noricense JCM 15102(T) (96.9 and 91.1 %). The DNA G + C content of strain TGN-42-S1(T) was determined to be 69.2 mol %. Strain TGN-42-S1(T) showed low DNA-DNA relatedness with Hbt. jilantaiense CGMCC 1.5337(T) and Hbt. salinarum CGMCC 1.1958(T), the most closely related members of the genus Halobacterium. The phenotypic, chemotaxonomic, and phylogenetic properties suggested that strain TGN-42-S1(T) (=CGMCC 1.12575(T) =JCM 19908(T)) represents a new species of Halobacterium, for which the name Halobacterium rubrum sp. nov. is proposed.

Biological properties of carotenoids extracted from Halobacterium halobium isolated from a Tunisian solar saltern.

BACKGROUND: Bioactive molecules have received increasing attention due to their nutraceutical attributes and anticancer, antioxidant, antiproliferative and apoptosis-inducing properties. This study aimed to investigate the biological properties of carotenoids extracted from Archaea. METHODS: Halophilic Archaea strains were isolated from the brine of a local crystallizer pond (TS7) of a solar saltern at Sfax, Tunisia. The most carotenoid-producing strain (M8) was investigated on heptoma cell line (HepG2), and its viability was assessed by the MTT-test. The cells were incubated with different sub-lethal extract rates, with carotenoid concentrations ranging from 0.2 to 1.5 µM. Antioxidant activity was evaluated through exposing the cells to sub-lethal extract concentrations for 24 hours and then to oxidative stress induced by 60 µM arachidonic acid and 50 µM H2O2. RESULTS: Compared to non-treated cells, bacterial carotenoid extracts inhibited HepG2 cell viability (50%). A time and dose effect was observed, with cell viability undergoing a significant (P < 0.05) decrease with extract concentration. After exposure to oxidative stress, control cells underwent a significant (P < 0.05) decrease in viability as compared to the non-treated cells. CONCLUSIONS: The bacterial extracts under investigation were noted to exhibit the strongest free radical scavenging activity with high carotenoid concentrations. The carotenoid extract also showed significant antiproliferative activity against HepG2 human cancer cell lines.

Spherical particles of halophilic archaea correlate with exposure to low water activity--implications for microbial survival in fluid inclusions of ancient halite.

Viable extremely halophilic archaea (haloarchaea) have been isolated from million-year-old salt deposits around the world; however, an explanation of their supposed longevity remains a fundamental challenge. Recently small roundish particles in fluid inclusions of 22 000- to 34 000-year-old halite were identified as haloarchaea capable of proliferation (Schubert BA, Lowenstein TK, Timofeeff MN, Parker MA, 2010, Environmental Microbiology, 12, 440-454). Searching for a method to produce such particles in the laboratory, we exposed rod-shaped cells of Halobacterium species to reduced external water activity (a(w)). Gradual formation of spheres of about 0.4 µm diameter occurred in 4 M NaCl buffer of a(w) ≤ 0.75, but exposure to buffered 4 M LiCl (a(w) ≤ 0.73) split cells into spheres within seconds, with concomitant release of several proteins. From one rod, three or four spheres emerged, which re-grew to normal rods in nutrient media. Biochemical properties of rods and spheres were similar, except for a markedly reduced ATP content (about 50-fold) and an increased lag phase of spheres, as is known from dormant bacteria. The presence of viable particles of similar sizes in ancient fluid inclusions suggested that spheres might represent dormant states of haloarchaea. The easy production of spheres by lowering a(w) should facilitate their investigation and could help to understand the mechanisms for microbial survival over geological times.

Halobacterium piscisalsi Yachai et al. 2008 is a later heterotypic synonym of Halobacterium salinarum Elazari-Volcani 1957.

Halobacterium piscisalsi was proposed by Yachai et al. (2008), with a single strain, HPC1-2(T) (= BCC 24372(T) = JCM 14661(T) = PCU 302(T)), which was isolated from fermented fish (pla-ra) in Thailand. According to Yachai et al. (2008), the strain was closely related to Halobacterium salinarum based on 16S rRNA gene sequence comparisons and could be differentiated by low DNA-DNA relatedness values and different biochemical profiles compared with other species of the genus. The reanalysis of the 16S rRNA gene sequences and the DNA-DNA relatedness among H. piscisalsi JCM 14661(T) and H. salinarum strains JCM 8978(T), R1 and NRC-1 revealed that they all had exactly the same 16S rRNA gene sequence and shared more than 70 % DNA-DNA relatedness. In addition, the full-length DNA-dependent RNA polymerase subunit B (RpoB) protein sequence of H. piscisalsi JCM 14661(T) (607 amino acids) was the same as that of H. salinarum JCM 8978(T) and showed 94.7 and 96.7 % similarities with those of Halobacterium noricense JCM 15102(T) and Halobacterium jilantaiense JCM 13558(T), respectively. Despite the different biochemical properties described by Yachai et al. (2008), the characteristic phenotypic properties of H. piscisalsi agreed with those in the description of H. salinarum emended by Gruber et al. (2004). Therefore, H. piscisalsi Yachai et al. (2008) should be regarded as a later heterotypic synonym of H. salinarum Elazari-Volcani 1957.

Haloarchaeal diversity in 23, 121 and 419 MYA salts.

DNA was extracted from surface-sterilized salt of different geological ages (23, 121, 419 million years of age, MYA) to investigate haloarchaeal diversity. Only Haloarcula and Halorubrum DNA was found in 23 MYA salt. Older crystals contained unclassified groups and Halobacterium. The older crystals yielded a unique 55-bp insert within the 16S rRNA V2 region. The secondary structure of the V2 region completely differed from that in haloarchaea of modern environments. The DNA demonstrates that unknown haloarchaea and the Halobacterium were key components in ancient hypersaline environments. Halorubrum and Haloarcula appear to be a dominant group in relatively modern hypersaline habitats.

Organic solvent tolerance of Halobacterium sp. SP1(1) and its extracellular protease.

Halophilic archaea belonging to three different genera- Halobacterium, Haloarcula and Haloferax, were isolated from Kandla salt pans. The isolates had an optimum requirement of 25% NaCl for growth. Increase in organic solvent tolerance of isolates was observed at higher NaCl concentrations. Among the three isolates Halobacterium sp. SP1(1) was found to be more tolerant than Haloarcula sp. SP2(2) and Haloferax sp. SP1(2a). The extracellular protease of Halobacterium sp. SP1(1) showed higher solvent tolerance compared to the organism itself. The enzyme was highly tolerant to toluene, xylene, n-decane, n-dodecane and n-undecane, majority of which are frequently used in paints. These findings may help in understanding the mechanism of organic solvent tolerance in halophilic archaea and their application in antifouling coatings. Also, best to our knowledge the present study is the first report on organic solvent tolerance of haloarchaeal extracellular protease.

Halobacterium piscisalsi sp. nov., from fermented fish (pla-ra) in Thailand.

A Gram-negative, motile, rod-shaped, extremely halophilic archaeon, designated strain HPC1-2(T), was isolated from pla-ra, a salt-fermented fish product of Thailand. Strain HPC1-2(T) was able to grow at 20-60 degrees C (optimum at 37-40 degrees C), at 2.6-5.1 M NaCl (optimum at 3.4-4.3 M NaCl) and at pH 5.0-8.0 (optimum at pH 7.0-7.5). Hypotonic treatment with less than 1.7 M NaCl caused cell lysis. The major polar lipids of the isolate were C(20)C(20) derivatives of phosphatidylglycerol, methylated phosphatidylglycerol phosphate, phosphatidylglycerol sulfate, triglycosyl diether, sulfated triglycosyl diether and sulfated tetraglycosyl diether. The G+C content of the DNA was 65.5 mol%. 16S rRNA gene sequence analysis indicated that the isolate represented a member of the genus Halobacterium in the family Halobacteriaceae. Based on 16S rRNA gene sequence similarity, strain HPC1-2(T) was related most closely to Halobacterium salinarum DSM 3754(T) (99.2%) and Halobacterium jilantaiense JCM 13558(T) (97.8%). However, low levels of DNA-DNA relatedness suggested that strain HPC1-2(T) was genotypically different from these closely related type strains. Strain HPC1-2(T) could also be differentiated based on physiological and biochemical characteristics. Therefore, strain HPC1-2(T) is considered to represent a novel species of the genus Halobacterium, for which the name Halobacterium piscisalsi sp. nov. is proposed. The type strain is HPC1-2(T) (=BCC 24372(T)=JCM 14661(T)=PCU 302(T)).

Halobacterium jilantaiense sp. nov., a halophilic archaeon isolated from a saline lake in Inner Mongolia, China.

A novel halophilic archaeon, NG4(T), was isolated from Jilantai salt lake in Inner Mongolia, China. The taxonomy of strain NG4(T) was studied by polyphasic methods. Strain NG4(T) grew at pH 5.5-8.5 and at a temperature of 22-55 degrees C. It was chemo-organotrophic, aerobic and required concentrations of 2.7-5.2 M NaCl and 0.05-0.3 M Mg(2+) for growth. Cells were Gram-negative, slender rods. Colonies on agar plates containing 25 % (w/v) total salts were red, elevated and round. According to 16S rRNA gene sequence similarity, strain NG4(T) was phylogenetically related to Halobacterium salinarum DSM 3754(T) (98.2 %) and Halobacterium noricense A1(T) (97.3 %). The DNA G+C content was 64.2 mol%. DNA-DNA relatedness values with Hbt. salinarum DSM 3754(T) and Hbt. noricense A1(T) were 47 and 35 %, respectively. The polar lipids of strain NG4(T) consisted of phosphatidylglycerol, methylated phosphatidylglycerol phosphate, phosphatidylglycerol sulfate, triglycosyl diether, sulfated triglycosyl diether and sulfated tetraglycosyl diether. It was concluded that strain NG4(T) represents a novel species of the genus Halobacterium, for which the name Halobacterium jilantaiense sp. nov. is proposed. The type strain is NG4(T) (=CGMCC 1.5337(T)=JCM 13558(T)).

Microbial diversity in Maras salterns, a hypersaline environment in the Peruvian Andes.

Maras salterns are located 3,380 m above sea level in the Peruvian Andes. These salterns consist of more than 3,000 little ponds which are not interconnected and act as crystallizers where salt precipitates. These ponds are fed by hypersaline spring water rich in sodium and chloride. The microbiota inhabiting these salterns was examined by fluorescence in situ hybridization (FISH), 16S rRNA gene clone library analysis, and cultivation techniques. The total counts per milliliter in the ponds were around 2 x 10(6) to 3 x 10(6) cells/ml, while the spring water contained less than 100 cells/ml and did not yield any detectable FISH signal. The microbiota inhabiting the ponds was dominated (80 to 86% of the total counts) by Archaea, while Bacteria accounted for 10 to 13% of the 4',6'-diamidino-2-phenylindole (DAPI) counts. A total of 239 16S rRNA gene clones were analyzed (132 Archaea clones and 107 Bacteria clones). According to the clone libraries, the archaeal assemblage was dominated by microorganisms related to the cosmopolitan square archaeon "Haloquadra walsbyi," although a substantial number of the sequences in the libraries (31% of the 16S rRNA gene archaeal clones) were related to Halobacterium sp., which is not normally found in clone libraries from solar salterns. All the bacterial clones were closely related to each other and to the gamma-proteobacterium "Pseudomonas halophila" DSM 3050. FISH analysis with a probe specific for this bacterial assemblage revealed that it accounted for 69 to 76% of the total bacterial counts detected with a Bacteria-specific probe. When pond water was used to inoculate solid media containing 25% total salts, both extremely halophilic Archaea and Bacteria were isolated. Archaeal isolates were not related to the isolates in clone libraries, although several bacterial isolates were very closely related to the "P. halophila" cluster found in the libraries. As observed for other hypersaline environments, extremely halophilic bacteria that had ecological relevance seemed to be easier to culture than their archaeal counterparts.

Halobacterium noricense sp. nov., an archaeal isolate from a bore core of an alpine Permian salt deposit, classification of Halobacterium sp. NRC-1 as a strain of H. salinarum and emended description of H. salinarum.

Two rod-shaped haloarchaeal strains, A1 and A2, were isolated from a bore core from a salt mine in Austria. The deposition of the salt is thought to have occurred during the Permian period (225-280 million years ago). The 16S rDNA sequences of the strains were 97.1% similar to that of the type species of the genus Halobacterium, which was also determined in this work. Polar lipids consisted of C20-C20 derivatives of phosphatidylglycerol, methylated phosphatidylglycerol phosphate, phosphatidylglycerol sulfate, triglycosyl diether and sulfated tetraglycosyl diether. Optimal salinity for growth was 15-17.5% NaCl; Mg++ was tolerated up to a concentration of 1 M. The DNA-DNA reassociation value of strain A1T was 25% with H. salinarum DSM 3754T and 41% with Halobacterium sp. NRC-1, respectively. Based on these results and other properties, e.g. whole cell protein patterns, menaquinone content and restriction patterns of DNA, strains A1 and A2 are members of a single species, for which we propose the name H. noricense. The type strain is A1 (DSM 15987T, ATCC BAA-852T, NCIMB 13967T). Since we present evidence that Halobacterium sp. NRC-1 is a member of H. salinarum, an emended description of H. salinarum is provided.

Purification and characterization of an extremely halophilic acetoacetyl-CoA thiolase from a newly isolated Halobacterium strain ZP-6.

The extremely halophilic archaeon ZP-6 was isolated from Ai-Ding salt lake in Xinjiang Uighur Autonomous Region of the People's Republic of China. Based on its physiological properties, 16S rDNA sequence, and DNA-DNA homology with known haloarchaea, the isolate was tentatively identified as a Halobacterium sp. An acetoacetyl-CoA thiolase was purified and characterized from this organism. The native enzyme has a molecular mass of 80 +/- 8 kDa and consists of two identical subunits of 43 +/- 2 kDa each. The N-terminus 14 amino acid residues were sequenced and showed identity with the respective part of a putative thiolase (AcaB1) of Halobacterium sp. NRC-1. The purified enzyme has an optimal pH of 7.9 for acetoacetyl-CoA thiolysis. The thiolytic activity was inhibited by the presence of Mg'- and was stimulated by KCl or NaCl. The thiolysis reaction of Halobacterium sp. ZP-6 thiolase can be inhibited by either substrate when present in excess. The distinct kinetic profile indicates that the thiolase from Halobacterium sp. ZP-6 may have a different catalytic mechanism from the so-called ping-pong mechanism employed by other thiolases. To our knowledge, this is the first report of the purification and characterization of a halophilic thiolase from an archaeal species.

Microorganismos halófitos: potencial biotecnológico e interés farmacéutico / Biotechnological potential and pharmaceutical interest of Halophilic Microorganisms

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