A new bacterial tRNA enhances antibiotic production in Streptomyces by circumventing inefficient wobble base-pairing.

We report the discovery and functional characterization of a new bacterial tRNA species. The tRNA-Asp-AUC, from a fast-growing desert streptomycete, decodes GAU codons. In the absence of queuosine tRNA anticodon modification in streptomycetes, the new tRNA circumvents inefficient wobble base-pairing during translation. The tRNA, which is constitutively expressed, greatly enhances synthesis of 4 different antibiotics in the model mesophilic species Streptomyces coelicolor, including the product of a so-called cryptic pathway, and increases yields of medically-important antibiotics in other species. This can be rationalised due to increased expression of both pleiotropic and pathway-specific transcriptional activators of antibiotic biosynthesis whose genes generally possess one or more GAT codons; the frequency of this codon in these gene sets is significantly higher than the average for streptomycete genes. In addition, the tRNA enhances production of cobalamin, a precursor of S-adenosyl methionine, itself an essential cofactor for synthesis of many antibiotics. The results establish a new paradigm of inefficient wobble base-pairing involving GAU codons as an evolved strategy to regulate gene expression and, in particular, antibiotic biosynthesis. Circumventing this by expression of the new cognate tRNA offers a generic strategy to increase antibiotic yields and to expand the repertoire of much-needed new bioactive metabolites produced by these valuable bacteria.

Nonribosomal antibacterial peptides isolated from Streptomyces agglomeratus 5-1-3 in the Qinghai-Tibet Plateau.

BACKGROUND: New antibiotics are urgently needed in clinical treatment of superdrug-resistant bacteria. Nonribosomal peptides (NRPs) are a major source of antibiotics because they exhibit structural diversity, and unique antibacterial mechanisms and resistance. Analysis of gene clusters of S. agglomeratus 5-1-3 showed that Clusters 3, 6, 12, 21, and 28 were used to synthesize NRPs. Here, we examined secondary metabolites of S. agglomeratus 5-1-3 isolated from soils in the Qinghai-Tibet Plateau, China, for NRPs with antibacterial activity. RESULTS: We isolated a total of 36 Streptomyces strains with distinct colony morphological characteristics from 7 soil samples. We screened 8 Streptomyces strains resistant to methicillin-resistant Staphylococcus aureus (MRSA). We then selected S. agglomeratus 5-1-3 for further study based on results of an antibacterial activity test. Here, we isolated three compounds from S. agglomeratus 5-1-3 and characterized their properties. The crude extract was extracted with ethyl acetate and purified with column chromatography and semipreparative high-performance liquid chromatography (HPLC). We characterized the three compounds using NMR analyses as echinomycin (1), 5,7,4'-trihydroxy-3.3',5'-trimethoxy flavone (2), and 2,6,2', 6'-tetramethoxy-4,4-bis(2,3-epoxy-1-hydroxypropyl)-biphenyl (3). We tested the antibacterial activity of pure compounds from strain 5-1-3 with the Oxford cup method. NRP echinomycin (1) showed excellent anti-MRSA activity with a minimum inhibitory concentration (MIC) of 2.0 µg/mL. Meanwhile, MIC of compound 2 and 3 was 128.0 µg/mL for both. In addition, 203 mg of echinomycin was isolated from 10 L of the crude extract broth of strain 5-1-3. CONCLUSION: In this study, S. agglomeratus 5-1-3 with strong resistance to MRSA was isolated from the soils in the Qinghai-Tibet Plateau. Strain 5-1-3 had a high yield of echinomycin (1) an NRP with a MIC of 2 µg/mL against MRSA. We propose that echinomycin derived from S. agglomeratus 5-1-3 may be a potent antibacterial agent for pharmaceutical use.

Seasonal Variation of Hypolithic Microbiomes in the Gobi Desert : Seasonal Variation of Hypolithic Microbiomes in the Gobi Desert.

Understanding how microbial communities adapt to environmental stresses is critical for interpreting ecological patterns and microbial diversity. In the case of the Gobi Desert, little is known on the environmental factors that explain hypolithic colonization under quartz stones. By analyzing nine hypolithic communities across an arid gradient and the effects of the season of the year in the Hexi Corridor of this desert, we found a significant decrease in hypolithic colonization rates (from 47.24 to 15.73%) with the increasing drought gradient and found two distinct communities in Hot and Cold samples, which survived or proliferated after a hot or a cold period. While Cold communities showed a greater species diversity and a predominance of Cyanobacteria, Hot communities showed a predominance of members of the Proteobacteria and the Firmicutes. In comparison, Cold communities also possessed stronger functions in the photosynthesis and carbon metabolism. Based on the findings of this study, we proposed that the hypolithic communities of the Hexi Corridor of the Gobi Desert might follow a seasonal developmental cycle in which temperature play an important role. Thus after a critical thermal threshold is crossed, heterotrophic microorganisms predominate in the hot period, while Cyanobacteria predominate in the cold period.

Comparative genomics reveals environmental adaptability and antimicrobial activity of a novel Streptomyces isolated from soil under black Gobi rocks.

A novel Streptomyces strain, designated 3_2T, was isolated from soil under the black Gobi rock sample of Northwest China. The taxonomic position of this strain was revealed by a polyphasic approach. Comparative analysis of the 16S rRNA gene sequences indicated that 3_2T was closely related to the members of the genus Streptomyces, with the highest similarity to Streptomyces rimosus subsp. rimosus CGMCC 4.1438 (99.17%), Streptomyces sioyaensis DSM 40032 (98.97%). Strain 3_2T can grow in media up to 13% NaCl. The genomic DNA G + C content of strain 3_2T was 69.9%. We obtained the genomes of 22 Streptomyces strains similar to strain 3_2T, compared the average nucleotide similarity, dDDH and average amino acid identity, and found that the genomic similarity of the new isolate 3_2T to all strains was below the threshold for interspecies classification. Chemotaxonomic data revealed that strain 3_2T possessed MK-9 (H6) and MK-9 (H8) as the major menaquinones. The cell wall contained LL-diaminopimelic acid (LL-DAP) and the whole-cell sugars were ribose and glucose. The major fatty acid methyl esters were iso-C16:0 (23.6%) and anteiso-C15:0 (10.4%). The fermentation products of strain 3_2T were inhibitory to Staphylococcus aureus and Bacillus thuringiensi. The genome of 3_2T was further predicted using anti-smash and the strain was found to encode the production of 41 secondary metabolites, and these gene clusters may be key to the good inhibitory activity exhibited by the strain. Genomic analysis revealed that strain 3_2T can encode genes that produce a variety of genes in response to environmental stresses, including cold shock, detoxification, heat shock, osmotic stress, oxidative stress, and these genes may play a key role in the harsh environment in which the strain can survive. Therefore, this strain represents a novel Streptomyces species, for which the name Streptomyces halobius sp. nov. is proposed. The type strain is 3_2T (= JCM 34935T = GDMCC 4.217T).

A novel UV-resistant bacterium Sphingomonas endolithica sp. nov., and genomic analysis, isolated from the north slope of Mount Everest.

Gram-stain-negative, aerobic, rod-shaped, non-motile bacterium strain ZFBP2030T was isolated from a rock on the North slope of Mount Everest. This strain contained a unique ubiquinone-10 (Q-10) as a predominant respiratory quinone. Among the tested fatty acids, the strain contained summed feature 8, C14:0 2OH, and C16:0, as major cellular fatty acids. The polar lipid profile contained phosphatidyl glycerol, phosphatidyl ethanolamine, three unidentified phospholipids, two unidentified aminolipids, and six unidentified lipids. The cell-wall peptidoglycan was a meso-diaminopimelic acid, and cell-wall sugars were ribose and galactose. Phylogenetic analyses based on 16S rRNA gene sequence revealed that strain ZFBP2030T was a member of the genus Sphingomonas, exhibiting high sequence similarity to the 16S rRNA gene sequences of Sphingomonas aliaeris DH-S5T (97.9%), Sphingomonas alpina DSM 22537T (97.3%) and Sphingomonas hylomeconis CCTCC AB 2013304T (97.0%). The 16S rRNA gene sequence similarity between ZFBP2030T and other typical strains was less than 97.0%. The average amino acid identity values, average nucleotide identity, and digital DNA-DNA hybridization values between strain ZFBP2030T and its highest sequence similarity strains were 56.9-79.9%, 65.1-82.2%, and 19.3-25.8%, respectively. The whole-genome size of the novel strain ZFBP2030T was 4.1 Mbp, annotated with 3838 protein-coding genes and 54 RNA genes. Moreover, DNA G + C content was 64.7 mol%. Stress-related functions predicted in the subsystem classification of the strain ZFBP2030T genome included osmotic, oxidative, cold/heat shock, detoxification, and periplasmic stress responses. The overall results of this study clearly showed that strain ZFBP2030T is a novel species of the genus Sphingomonas, for which the name Sphingomonas endolithica sp. nov. is proposed. The type of strain is ZFBP2030T (= EE 013T = GDMCC 1.3123T = JCM 35386T).

Nocardioides: "Specialists" for Hard-to-Degrade Pollutants in the Environment.

Nocardioides, a genus belonging to Actinomycetes, can endure various low-nutrient conditions. It can degrade pollutants using multiple organic materials such as carbon and nitrogen sources. The characteristics and applications of Nocardioides are described in detail in this review, with emphasis on the degradation of several hard-to-degrade pollutants by using Nocardioides, including aromatic compounds, hydrocarbons, haloalkanes, nitrogen heterocycles, and polymeric polyesters. Nocardioides has unique advantages when it comes to hard-to-degrade pollutants. Compared to other strains, Nocardioides has a significantly higher degradation rate and requires less time to break down substances. This review can be a theoretical basis for developing Nocardioides as a microbial agent with significant commercial and application potential.

Transcriptional and biochemical analyses of Planomicrobium strain AX6 from Qinghai-Tibetan Plateau, China, reveal hydrogen peroxide scavenging potential.

BACKGROUND: The bacterial mechanisms responsible for hydrogen peroxide (H2O2) scavenging have been well-reported, yet little is known about how bacteria isolated from cold-environments respond to H2O2 stress. Therefore, we investigated the transcriptional profiling of the Planomicrobium strain AX6 strain isolated from the cold-desert ecosystem in the Qaidam Basin, Qinghai-Tibet Plateau, China, in response to H2O2 stress aiming to uncover the molecular mechanisms associated with H2O2 scavenging potential. METHODS: We investigated the H2O2-scavenging potential of the bacterial Planomicrobium strain AX6 isolated from the cold-desert ecosystem in the Qaidam Basin, Qinghai-Tibet Plateau, China. Furthermore, we used high-throughput RNA-sequencing to unravel the molecular aspects associated with the H2O2 scavenging potential of the Planomicrobium strain AX6 isolate. RESULTS: In total, 3,427 differentially expressed genes (DEGs) were identified in Planomicrobium strain AX6 isolate in response to 4 h of H2O2 (1.5 mM) exposure. Besides, Kyoto Encyclopedia of Genes and Genomes pathway and Gene Ontology analyses revealed the down- and/or up-regulated pathways following H2O2 treatment. Our study not only identified the H2O2 scavenging capability of the strain nevertheless also a range of mechanisms to cope with the toxic effect of H2O2 through genes involved in oxidative stress response. Compared to control, several genes coding for antioxidant proteins, including glutathione peroxidase (GSH-Px), Coproporphyrinogen III oxidase, and superoxide dismutase (SOD), were relatively up-regulated in Planomicrobium strain AX6, when exposed to H2O2. CONCLUSIONS: Overall, the results suggest that the up-regulated genes responsible for antioxidant defense pathways serve as essential regulatory mechanisms for removing H2O2 in Planomicrobium strain AX6. The DEGs identified here could provide a competitive advantage for the existence of Planomicrobium strain AX6 in H2O2-polluted environments.

Efficient degradation of hydroquinone by a metabolically engineered Pseudarthrobacter sulfonivorans strain.

Pseudarthrobacter sulfonivorans strain Ar51 can degrade crude oil and multi-substituted benzene compounds efficiently at low temperatures. However, it cannot degrade hydroquinone, which is a key intermediate in the degradation of several other compounds of environmental importance, such as 4-nitrophenol, g-hexachlorocyclohexane, 4-hydroxyacetophenone and 4-aminophenol. Here we co-expressed the two subunits of hydroquinone dioxygenase from Sphingomonas sp. strain TTNP3 with different promoters in the strain Ar51. The strain with 2 hdnO promoters exhibited the strongest hydroquinone catabolic activity. However, in the absence of antibiotic selection this ability to degrade hydroquinone was lost due to plasmid instability. Consequently, we constructed a hisD knockout strain, which was unable to synthesise histidine. By introducing the hisD gene onto the plasmid, the ability to degrade hydroquinone in the absence of antibiotic selection was stabilised. In addition, to make the strain more stable for industrial applications, we knocked out the recA gene and integrated the hydroquinone dioxygenase genes at this chromosomal locus. This strain exhibited the strongest activity in catabolizing hydroquinone, up to 470 mg/L in 16 h without antibiotic selection. In addition, this activity was shown to be stable when the strain has cultured in medium without antibiotic selection after 20 passages.

Streptomyces gobiensis sp. nov., an antimicrobial producing actinobacterium isolated from soil under black Gobi rocks.

A novel actinomycete, strain 1_25T, was isolated from soil under a black Gobi rock sample from Shuangta, PR China, and characterized using a polyphasic taxonomic approach. The results of comparative analysis of the 16S rRNA gene sequences indicated the 1_25T represented a member of the genus Streptomyces. Chemotaxonomic data revealed that 1_25T possessed MK-9(H8) as the major menaquinone. The cell wall contained ll-diaminopimelic acid (ll-DAP) and the whole-cell sugar pattern consisted of ribose, glucose and galactose. Major fatty acid methyl esters were observed to be iso-C16 : 0 (23.6 %), and anteiso-C15 : 0 (10.4 %). The genomic DNA G+C content of 1_25T was 69 mol %. The results of phylogenetic analysis based on 16S rRNA gene sequence indicated that 1_25T had high sequence similarity with Streptomyces qinglanensis 172205T (98.1 %), Streptomyces lycii TRM 66187T (98 %), and Streptomyces griseocarneus JCM4580T (98 %). In addition to the differences in phenotypic characters, the average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between 1_25T and closely related species were below the recommended threshold values for assigning strains to the same species. The fermentation product of 1_25T in ISP2 had an inhibitory effect on Staphylococcus aureus. On the basis of these genotypic and phenotypic characteristics, strain 1_25T (=JCM 34936T=GDMCC 4.216T) represents a novel species of the genus Streptomyces, for which the name Streptomyces gobiensis sp. nov. is proposed.

Sphingomonas radiodurans sp. nov., a novel radiation-resistant bacterium isolated from the north slope of Mount Everest.

A bacterial strain, designated S9-5T, was isolated from moraine samples collected from the north slope of Mount Everest at an altitude of 5 500 m above sea level. A polyphasic study confirmed the affiliation of the strain with the genus Sphingomonas. Strain S9-5T was an aerobic, Gram-stain-negative, non-spore-forming, non-motile and rod-shaped bacterium that could grow at 10-40 °C, pH 5-8 and with 0-9 % (w/v) NaCl. Q-10 was its predominant respiratory menaquinone. Diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, an unidentified phospholipid, an unidentified aminophospholipid and eight unidentified lipids comprised the polar lipids of strain S9-5T. Its major fatty acids were summed feature 8 (C18 : 1 ω7c and/or C18 : 1 ω6c) and C16 : 0. The G+C content was 65.75mol%. Phylogenetic analysis based on 16S rRNA sequences showed that strain S9-5T was phylogenetically closely related to Sphingomonas panaciterrae DCY91T (98.17 %), Sphingomonas olei K-1-16T (98.11 %) and Sphingomonas mucosissima DSM 17494T (97.39 %). The average nucleotide identity values among strain S9-5T and Sphingomonas panaciterrae DCY91T, Sphingomonas olei K-1-16T and Sphingomonas mucosissima DSM 17494T were 78.82, 78.87 and 78.29 %, respectively. Based on the morphological, physiological and chemotaxonomic data, strain S9-5T (=JCM 34750T=GDMCC 1.2714T) should represent a novel species of the genus Sphingomonas, for which we propose the name Sphingomonas radiodurans sp. nov.

Paracoccus everestensis sp. nov., a novel bacterium with great antioxidant capacity isolated from the north slope of Mount Everest.

A bacterial strain, designated S8-55T, was isolated from moraine samples collected from the north slope of Mount Everest at an altitude of 5 500 m above sea level. The purpose of this study was to describe a novel species and its characteristics, through genome sequencing and analysis of the relationship between the members of the genus Paracoccus, and explore the antioxidant capacity of strain S8-55T. The polyphasic study confirmed the affiliation of strain S8-55T with the genus Paracoccus. Strain S8-55T was aerobic, Gram-negative and oxidase- and catalase positive. Cells were orange-pigmented, ellipsoid and had no spore formation, no flagella and no motility. Strain S8-55T grow at 10-37 °C, pH 7-11 and without NaCl. Ubiquinone 10 was its predominant respiratory menaquinone. The polar lipids of strain S8-55T were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, phosphatidylcholine, an unidentified phospholipid, an unidentified aminolipid and three unidentified lipids. Its major fatty acids were summed feature 8 (C18 : 1 ω7c and/or C18 : 1 ω6c). The G+C content was 64.3 mol%. The phylogenetic analysis based on the 16S rRNA sequence showed that strain S8-55T was closely related to Paracoccus angustae E6T (97.9 %), Paracoccus aerius 011410T (97.9 %) and Paracoccus hibisci THG-T2.8T (97.8 %). The average nucleotide identity values among strain S8-55T and P. angustae CCTCC AB 2015056T, P. aerius KCTC 42845T and P. hibisci CCTCC AB 2016181T were 84.1, 84.5 and 76.3 %, respectively. The genome of strain S8-55T contained antioxidant genes such as oxyR, recD, katE, recD and rpoH. Based on its morphological, physiological and chemical taxonomic characteristics, strain S8-55T (=JCM 35 227T=GDMCC 1.3026T) should be classified as a novel species of the genus Paracoccus with the proposed name Paracoccus everestensis sp. nov.

Arthrobacter antioxidans sp. nov., a blue pigment-producing species isolated from Mount Everest.

Bacteria in the genus Arthrobacter have been found in extreme environments, e.g. glaciers, brine and mural paintings. Here, we report the discovery of a novel pink-coloured bacterium, strain QL17T, capable of producing an extracellular water-soluble blue pigment. The bacterium was isolated from the soil of the East Rongbuk Glacier of Mt. Everest, China. 16S rRNA gene sequence analysis showed that strain QL17T was most closely related to the species Arthrobacter bussei KR32 T. However, compared to A.bussei KR32T and the next closest relatives, the new species demonstrates considerable phylogenetic distance at the whole-genome level, with an average nucleotide identity of <85 % and inferred DNA-DNA hybridization of <30 %. Polyphasic taxonomy results support our conclusion that strain QL17T represents a novel species of the genus Arthrobacter. Strain QL17T had the highest tolerance to hydrogen peroxide at 400 mM. Whole-genome sequencing of strain QL17T revealed the presence of numerous cold-adaptation, antioxidation and UV resistance-associated genes, which are related to adaptation to the extreme environment of Mt. Everest. Results of this study characterized a novel psychrotolerant Arthrobacter species, for which the name Arthrobacter antioxidans sp. nov. is proposed. The type strain is QL17T (GDMCC 1.2948T=JCM 35246T).

Magnetoelectric and Magnetostrictive Effects in Scheelite-Type HoCrO4.

Scheelite-type HoCrO4 was prepared by treating the ambient-pressure zircon-type precursor phase under 8 GPa and 700 K. A long-range antiferromagnetic phase transition is found to occur at TN ≈ 23 K due to the spin order of Ho3+ and Cr5+ magnetic ions. However, the antiferromagnetic ground state is sensitive to an external magnetic field and a moderate field of about 1.1 T can induce a metamagnetic transition, giving rise to the presence of a large magnetization up to 8.5 µB/f.u. at 2 K and 7 T. Considerable linear magnetoelectric effect is observed in the antiferromagnetic state, while the induced electric polarization experiences a sharp increase near the critical field of the metamagnetic transition. Ferromagnetism and ferroelectricity thus rarely coexist under higher magnetic fields in scheelite-type HoCrO4. Moreover, a magnetic field also plays an important role in the longitudinal constriction of HoCrO4, and a significant magnetostrictive effect with a value of up to 300 ppm is observed at 2 K and 9 T, which can be attributed to the strong anisotropy of the rare-earth Ho3+ ion. Possible coupling between magnetoelectric and magnetoelastic effects is discussed.

Bacterial diversity patterns of desert dunes in the northeastern Qinghai-Tibet Plateau, China.

Limited knowledge about the variation patterns of bacterial community composition in the sand and vegetative ecosystems confines our understanding regarding the contribution of the sand dune to desert areas. In this study, 454 pyrosequencing platforms were adopted to determine the community structure of bacteria and diversity of sand dunes in northeastern Qinghai-Tibet Plateau, China: 50 cm deep, rhizosphere, physical crusts, and biological crusts representing sand and vegetative ecosystems, respectively. The findings revealed significant variation in bacterial diversities and the structure of communities in the sand and vegetative ecosystems. The dominant bacterial phyla of sand and vegetative ecosystems were Firmicutes (47%), Actinobacteria (21%), Proteobacteria (16%), and Bacteroidetes (13%), while Lactococcus (50%) was found to be the dominant genus. Furthermore, samples with high alpha-diversity indices (Chao 1 and Shannon) for the vegetative ecosystem have the lowest modularity index and the largest number of biomarkers, with some exceptions. Redundancy analysis exhibited that environmental factors could explain 72% (phyla) and 67% (genera) of the bacterial communities, with EC, TC, and TOC being the major driving factors. This study expands our understanding of bacterial community composition in the desert ecosystem. The findings suggest that variations in the sand and vegetative ecosystems, such as those predicted by environmental factors, may reduce the abundance and diversity of bacteria, a response that likely affects the provision of key ecosystem processes by desert regions.

Mesobacillus harenae sp. nov., isolated from the sandy soil of a cold desert.

A bacterial strain, designated Y40T, was isolated from sandy soil sampled on the Qinghai-Tibet Plateau. A polyphasic study confirmed the affiliation of the strain with the genus Mesobacillus. Strain Y40T was found to be an aerobic, Gram-stain-positive, motile and rod-shaped bacterium. The strain grew at 10-42 °C, pH 6-9 and with 0-2 % (w/v) NaCl. The diagnostic amino acid was meso-diaminopimeilic acid. MK7 was predominant menaquinone, and iso-C15:0, iso-C17:1 ω10c and anteiso-C15:0 were the major fatty acids. The polar lipids were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine and an unidentified lipid. The DNA G+C content was 40.6 mol%. Based on he results of 16S rRNA gene sequence analysis, strain Y40T was phylogenetically closely related to Mesobacillus zeae JJ-247T and Mesobacillus foraminis CV53T, with similarities of 98.0 and 97.7 %, respectively. The average nucleotide identity (ANIb) values between strain Y40T and Mesobacillus zeae JJ-247T and Mesobacillus foraminis CV53T were 69.9 and 70.0 %, respectively. Based on the morphological, physiological, and chemotaxonomic data, it is proposed that strain Y40T (=CICC 24459T=JCM 32794T) should be classified into the genus Mesobacillus as Mesobacillus harenae sp. nov.

Seasonal Variation in Fungal Community Composition Associated with Tamarix chinensis Roots in the Coastal Saline Soil of Bohai Bay, China.

Coastal salinity typically alters the soil microbial communities, which subsequently affect the biogeochemical cycle of nutrients in the soil. The seasonal variation of the soil fungal communities in the coastal area, closely associated with plant population, is poorly understood. This study provides an insight into the fungal community's variations from autumn to winter and spring to summer at a well-populated area of salt-tolerant Tamarix chinensis and beach. The richness and diversity of fungal community were higher in the spring season and lower in the winter season, as showed by high throughput sequencing of the 18S rRNA gene. Ascomycota was the predominant phylum reported in all samples across the region, and higher difference was reported at order level across the seasonal variations. The redundancy analysis suggested that the abundance and diversity of fungal communities in different seasons are mainly correlated to total organic carbon and total nitrogen. Additionally, the saprotrophic and pathotrophic fungi decreased while symbiotic fungi increased in the autumn season. This study provides a pattern of seasonal variation in fungal community composition that further broadens our limited understanding of how the density of the salt-tolerant T. chinensis population of the coastal saline soil could respond to their seasonal variations.

High-Pressure Synthesis and Magnetism of the 4H-BaMnO3 Single Crystal and Its 6H-Type Polymorph.

A 4H-type BaMnO3 single crystal was prepared by combining the floating zone method with high-pressure treatment at 5 GPa and 1023 K. The crystal crystallizes to a hexagonal structure with space group P63/mmc and lattice parameters a = 5.63723(5) Å and c = 9.22355(8) Å. In this structure, face-sharing MnO6 octahedral dimers connect with each other by corner O atoms along the c-axis direction, forming an -A-B-A-C-type 4H arrangement. A long-range antiferromagnetic (AFM) phase transition is found to occur at TN ≈ 263 K. When the synthesis pressure increases to 20 GPa, a new polymorphic phase is obtained. This higher-pressure phase still possesses the hexagonal P63/mmc symmetry, but the lattice parameters change to be a = 5.61349(2) Å and c = 13.66690(9) Å with a unit cell volume reduction of 2.05%. In this new phase, the c-axis MnO6 dimers are separated by MnO6 octahedral layers in the ab plane, forming an -A-B-C-A-C-B-type 6H structure. The 6H phase exhibits two long-range AFM orderings at TN1 ≈ 220 K and TN2 ≈ 25 K, respectively. The different magnetic properties are discussed on the basis of the detailed structural constitutions of 4H- and 6H-BaMnO3.

Massilia arenae sp. nov., isolated from sand soil in the Qinghai-Tibetan Plateau.

A bacterial strain, designated GEM5T, was isolated from sand soil samples from the Qinghai-Tibet Plateau. The polyphasic study confirmed the affiliation of the isolate with the genus Massilia. GEM5T had Gram-stain-negative, non-spore-forming and rod-shaped cells and grew at 4-30 °C, pH 6-8 and with 0-2 % (w/v) NaCl. Its cell wall contained ribose. Q8 was the predominant respiratory quinone, and summed feature 3 (C16 : 1ω6c/ω7c) and C16 : 0 were the major components of the fatty acids. The polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, an unidentified phospholipid, an unidentified aminolipid and four unidentified lipids. The DNA G+C content was 65.1 mol%. The phylogenetic analysis based on the 16S rRNA gene showed a stable clade being formed by GEM5T, Massilia timonae CCUG 45783T (97.94 %) and Massilia oculi CCUG 43427AT (97.58 %). The average nucleotide identity (ANIb) values between GEM5T and M. timonae CCUG 45783T, M.oculi CCUG 43427AT were 91.3 and 91.7 %, respectively. On the basis of the morphological, physiological and chemotaxonomic pattern, it was proposed that strain GEM5T (=JCM 32744T=CICC 24458T) should be classified as representing a member of the genus Massilia with the name Massilia arenae sp. nov.

Radiobacillus deserti gen. nov., sp. nov., a UV-resistant bacterium isolated from desert soil.

A Gram-stain-positive, aerobic, rod-shaped, non-motile, endospore-forming and UV-resistant bacterial strain, designated strain TKL69T, was isolated from sandy soil sampled in the Taklimakan Desert. The strain grew at 20-50 °C, pH 6-9 and with 0-12 % (w/v) NaCl. The major fatty acids were anteiso-C15 : 0, iso-C15 : 0 and C16 : 0. The only respiratory quinone was MK-7. The cell-wall peptidoglycan was meso-diaminopimelic acid. Diphosphatidyl glycerol, two unidentified aminophospholipids and one unidentified phospholipid were identified as the major polar lipids. Genomic DNA analysis revealed a G+C content of 38.5 mol%. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain TKL69T has the highest similarity to Salinibacillus xinjiangensis CGMCC 1.12331T (96.9 %) but belongs to an independent taxon separated from other genera of the family Bacillaceae. Phylogenetic, phenotypic and chemotaxonomic analyses suggested that strain TKL69T represents a novel species of a new genus, for which the name Radiobacillus gen. nov., sp. nov. is proposed, with the type strain being Radiobacillus deserti TKL69T (=JCM 33497T=CICC 24779T).

High-Pressure Synthesis of a B-site Co2+/Mn4+ Disordered Quadruple Perovskite LaMn3Co2Mn2O12.

A new oxide, LaMn3Co2Mn2O12, was synthesized under high-pressure (7 GPa) and high-temperature (1423 K) conditions. The compound crystallizes in an AA'3B4O12-type quadruple perovskite structure with space group Im3̅. The Rietveld structural analysis combined with soft X-ray absorption spectroscopy reveals the charge combination to be LaMn3+3Co2+2Mn4+2O12, where the La3+ and Mn3+ are 1:3 ordered respectively at the A and A' sites, whereas the Co2+ and Mn4+ are disorderly distributed at the B site. This is in sharp contrast to R2Co2+Mn4+O6 (R = La and rare earth) double perovskites, in which the Co2+ and Mn4+ charge states are always orderly distributed with a rocksalt-type fashion, giving rise to a long-range magnetic ordering. As a result, LaMn3Co2Mn2O12 displays spin glassy magnetic properties due to the random Co2+ and Mn4+ distribution, as demonstrated by dc and ac magnetic susceptibility as well as specific heat measurements. Possible factors that affect the B-site degree of order in perovskite structures are discussed.