Bioprospecting of Actinobacterial Diversity and Antibacterial Secondary Metabolites from the Sediments of Four Saline Lakes on the Northern Tibetan Plateau.

The Tibetan Plateau, known as the "Roof of the World" and "The Third Pole", harbors numerous saline lakes primarily distributed in the Northern Tibetan Plateau. However, the challenging conditions of high altitude, low oxygen level, and harsh climate have limited investigations into the actinobacteria from these saline lakes. This study focuses on investigating the biodiversity and bioactive secondary metabolites of cultivable actinobacteria isolated from the sediments of four saline lakes on the Northern Tibetan Plateau. A total of 255 actinobacterial strains affiliated with 21 genera in 12 families of 7 orders were recovered by using the pure culture technique and 16S rRNA gene phylogenetic analysis. To facilitate a high-throughput bioactivity evaluation, 192 isolates underwent OSMAC cultivation in a miniaturized 24-well microbioreactor system (MATRIX cultivation). The antibacterial activity of crude extracts was then evaluated in a 96-well plate antibacterial assay. Forty-six strains demonstrated antagonistic effects against at least one tested pathogen, and their underlying antibacterial mechanisms were further investigated through a dual-fluorescent reporter assay (pDualrep2). Two Streptomyces strains (378 and 549) that produce compounds triggering DNA damage were prioritized for subsequent chemical investigations. Metabolomics profiling involving HPLC-UV/vis, UPLC-QTOF-MS/MS, and molecular networking identified three types of bioactive metabolites belonging to the aromatic polyketide family, i.e., cosmomycin, kidamycin, and hedamycin. In-depth analysis of the metabolomic data unveiled some potentially novel anthracycline compounds. A genome mining study based on the whole-genome sequences of strains 378 and 549 identified gene clusters potentially responsible for cosmomycin and kidamycin biosynthesis. This work highlights the effectiveness of combining metabolomic and genomic approaches to rapidly identify bioactive chemicals within microbial extracts. The saline lakes on the Northern Tibetan Plateau present prospective sources for discovering novel actinobacteria and biologically active compounds.

Georgenia halotolerans sp. nov., a halotolerant actinobacterium isolated from Taklamakan desert soil.

A Gram-stain-positive, aerobic, non-motile, non-spore-forming and rod-shaped actinobacterium, designated strain 10Sc9-8T, was isolated from Taklamakan desert soil sampled in the Xinjiang Uygur Autonomous Region, China. Strain 10Sc9-8T grew at 8‒37 °C (optimum, 28‒30 °C), pH 6.0‒10.0 (optimum, pH 7.0-8.0) and in the presence of 0‒15 % (w/v) NaCl (optimum, 0-3 %). Phylogenetic analysis based on 16S rRNA gene sequence suggested that strain 10Sc9-8T was affiliated with members of the genus Georgenia and showed the highest 16S rRNA gene sequence similarity to Georgenia yuyongxinii Z443T (97.4 %). Phylogenomic analysis based on the whole genome sequences indicated that strain 10Sc9-8T should be assigned into the genus Georgenia. The average nucleotide identity and digital DNA-DNA hybridization values calculated from the whole genome sequences indicated that strain 10Sc9-8T was clearly separated from other closely related species of the genus Georgenia with values below the thresholds for species delineation. Chemotaxonomic analyses showed that the cell-wall peptidoglycan was in a variant of A4α type with an interpeptide bridge comprising l-Lys-l-Ala-Gly-l-Asp. The predominant menaquinone was MK-8(H4). The polar lipids comprised diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol, phosphatidylinositol mannoside, several unidentified phospholipids, glycolipids and one unidentified lipid. The major fatty acids were anteiso-C15 : 0, anteiso-C15 : 1 A and C16 : 0. The genomic DNA G+C content was 72.7 mol%. On the basis of phenotypic, phylogenetic and phylogenomic data, strain 10Sc9-8T represents a novel species of the genus Georgenia, for which the name Georgenia halotolerans sp. nov. is proposed. The type strain is 10Sc9-8T (=JCM 33946T=CPCC 206219T).

Exploring the Diversity and Antibacterial Potentiality of Cultivable Actinobacteria from the Soil of the Saxaul Forest in Southern Gobi Desert in Mongolia.

Saxaul (Haloxylon ammodendron) is the most widespread plant community in the Gobi Desert in Mongolia, which plays important roles in wind control, sand fixation and water conservation. Investigations of soil-derived actinobacteria inhabiting in the saxaul forest in Gobi Desert in Mongolia have been scarce. In this study, biodiversity of culturable actinobacteria isolated from soil of the saxaul forest in Southern Gobi Aimak (Southern Gobi Province) of Mongolia was characterized and their potential to produce compounds with antibacterial activities was assessed. A total of 172 actinobacterial strains were recovered by culture-based approaches and were phylogenetically affiliated into 22 genera in 13 families of seven orders. Forty-nine actinobacterial isolates were selected to evaluate the antibacterial activities and their underlying mechanism of action was screened by means of a dual-fluorescent reporter assay (pDualrep2). Twenty-three isolates exhibited antagonistic activity against at least one of the tested pathogens, of which two Streptomyces strains can attenuate protein translation by ribosome stalling. Combinational strategies based on modern metabolomics, including bioassay-guided thin-layer chromatography (TLC), UPLC-QTOF-MS/MS based structural annotation and enhanced molecular networking successfully annotated chloramphenicol, althiomycin and granaticin and their derivatives as the antibacterial compounds from extracts in three Streptomyces strains, respectively. This work demonstrates that UPLC-MS/MS-based structural identification and enhanced molecular networking are effective strategies to rapidly illuminate the bioactive chemicals in the microbial extracts. Meanwhile, our results show that the saxaul forest in Mongolia Gobi Desert is a prospective source for discovering novel actinobacteria and biologically active compounds.

Hoyosella lacisalsi sp. nov., a halotolerant actinobacterium isolated from the Lake Gudzhirganskoe.

A Gram-stain-positive, aerobic, non-motile, non-spore-forming and coccus-shaped strain, designated strain G463T, was isolated from the rhizosphere soil of Salicornia europaea L. collected from Lake Gudzhirganskoe in Siberia. Based on 16S rRNA gene phylogeny, strain G463T belonged to the genus Hoyosella, with the highest 16S rRNA gene sequence similarity to Hoyosella altamirensis DSM 45258T (96.1%). The major fatty acids were C17:1 ω8c, C16:0, C15 : 0 and C17:0. The strain contained meso-diaminopimelic acid as the cell-wall diagnostic diamino acid and arabinose, galactose and ribose as the whole-cell sugars. MK-8 and MK-7 were the predominant menaquinones. The polar lipid profile comprised diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylinositol, one unidentified phosphoglycolipid, two unidentified glycolipids and several unidentified lipids. Acetyl was the muramyl residue. Mycolic acids (C28-C34) were present. The G+C content of the genomic DNA was 68.3 mol%. Based on its phylogenetic, phenotypic and chemotaxonomic features, strain G463T was considered to represent a novel species of the genus Hoyosella, for which the name Hoyosella lacisalsi sp. nov. is proposed. The type strain is G463T (=JCM 33650T=CGMCC 1.17230T).

Metabolomics Tools Assisting Classic Screening Methods in Discovering New Antibiotics from Mangrove Actinomycetia in Leizhou Peninsula.

Mangrove actinomycetia are considered one of the promising sources for discovering novel biologically active compounds. Traditional bioactivity- and/or taxonomy-based methods are inefficient and usually result in the re-discovery of known metabolites. Thus, improving selection efficiency among strain candidates is of interest especially in the early stage of the antibiotic discovery program. In this study, an integrated strategy of combining phylogenetic data and bioactivity tests with a metabolomics-based dereplication approach was applied to fast track the selection process. A total of 521 actinomycetial strains affiliated to 40 genera in 23 families were isolated from 13 different mangrove soil samples by the culture-dependent method. A total of 179 strains affiliated to 40 different genera with a unique colony morphology were selected to evaluate antibacterial activity against 12 indicator bacteria. Of the 179 tested isolates, 47 showed activities against at least one of the tested pathogens. Analysis of 23 out of 47 active isolates using UPLC-HRMS-PCA revealed six outliers. Further analysis using the OPLS-DA model identified five compounds from two outliers contributing to the bioactivity against drug-sensitive A. baumannii. Molecular networking was used to determine the relationship of significant metabolites in six outliers and to find their potentially new congeners. Finally, two Streptomyces strains (M22, H37) producing potentially new compounds were rapidly prioritized on the basis of their distinct chemistry profiles, dereplication results, and antibacterial activities, as well as taxonomical information. Two new trioxacarcins with keto-reduced trioxacarcinose B, gutingimycin B (16) and trioxacarcin G (20), together with known gutingimycin (12), were isolated from the scale-up fermentation broth of Streptomyces sp. M22. Our study demonstrated that metabolomics tools could greatly assist classic antibiotic discovery methods in strain prioritization to improve efficiency in discovering novel antibiotics from those highly productive and rich diversity ecosystems.

Characterization and description of Faecalibacterium butyricigenerans sp. nov. and F. longum sp. nov., isolated from human faeces.

Exploiting a pure culture strategy to investigate the composition of the human gut microbiota, two novel anaerobes, designated strains AF52-21T and CM04-06T, were isolated from faeces of two healthy Chinese donors and characterized using a polyphasic approach. The two strains were observed to be gram-negative, non-motile, and rod-shaped. Both strains grew optimally at 37 °C and pH 7.0. Phylogenetic analysis based on 16S rRNA gene sequences revealed that the two strains clustered with species of the genus Faecalibacterium and were most closely related to Faecalibacterium prausnitzii ATCC 27768T with sequence similarity of 97.18% and 96.87%, respectively. The two isolates shared a 16S rRNA gene sequence identity of 98.69%. Draft genome sequencing was performed for strains AF52-21T and CM04-06T, generating genome sizes of 2.85 Mbp and 3.01 Mbp. The calculated average nucleotide identity values between the genomes of the strains AF52-21T and CM04-06T compared to Faecalibacterium prausnitzii ATCC 27768T were 83.20% and 82.54%, respectively, and 90.09% when comparing AF52-21T and CM04-06T. Both values were below the previously proposed species threshold (95-96%), supporting their recognition as novel species in the genus Faecalibacterium. The genomic DNA G + C contents of strains AF52-21T and CM04-06T calculated from genome sequences were 57.77 mol% and 57.51 mol%, respectively. Based on the phenotypic, chemotaxonomic and phylogenetic characteristics, we conclude that both strains represent two new Faecalibacterium species, for which the names Faecalibacterium butyricigenerans sp. nov. (type strain AF52-21T = CGMCC 1.5206T = DSM 103434T) and Faecalibacterium longum sp. nov. (type strain CM04-06T = CGMCC 1.5208T = DSM 103432T) are proposed.

Phycicoccus flavus sp. nov., a novel endophytic actinobacterium isolated from branch of Kandelia candel.

A Gram-stain-positive, aerobic, non-motile, non-endospore-forming and rod-shaped actinobacterium, designated strain CMS6Z-2T, was isolated from a surface-sterilized branch of Kandelia candel collected from the Maowei Sea, Guangxi Zhuang Autonomous Region, PR China. Strain CMS6Z-2T grew at 10-37 °C (optimum, 37 °C), pH 6.0-9.0 (optimum, pH 7.0-8.0) and in the presence of 0-10.0 % (w/v) NaCl (optimum, 0-1.0 %). Strain CMS6Z-2T possessed meso-diaminopimelic acid as the diamino acid of the peptidoglycan and MK-8 (H4) as the predominant menaquinone. The major fatty acids were iso-C15 : 0, C16 : 0 and C18 : 1 ω9c. The polar lipids comprised diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol and two unknown phospholipids. The G+C content of the genomic DNA was 74.1 mol%. Comparative analysis of 16S rRNA genes showed that strain CMS6Z-2T should be assigned to the genus Phycicoccus and its closest relative was Phycicoccus endophyticus IP6SC6T with 98.3 % similarity. Phylogenetic analyses based on 16S rRNA gene sequence and phylogenomic analysis based on core proteomes alignment revealed that strain CMS6Z-2T belonged to the genus Phycicoccus and formed a robust cluster with Phycicoccus endophyticus IP6SC6T within the genus Phycicoccus. The average nucleotide identity value and estimated digital DNA-DNA hybridization value between strain CMS6Z-2T and the type strain of Phycicoccus endophyticus were 81.5 and 23.9 %, respectively. On the basis of phylogenetic, phenotypic and chemotaxonomic characteristics, strain CMS6Z-2T represents a novel species of the genus Phycicoccus, for which the name Phycicoccus flavus sp. nov. is proposed. The type strain is CMS6Z-2T (=KCTC 49240T=CGMCC4.7549T).

Butyribacter intestini gen. nov., sp. nov., a butyric acid-producing bacterium of the family Lachnospiraceae isolated from human faeces, and reclassification of Acetivibrio ethanolgignens as Acetanaerobacter ethanolgignens gen. nov., comb. nov.

A novel, non-motile, Gram-stain-positive, non-spore-forming, obligate anaerobic bacterium, designated strain TF01-11T, was isolated from human faeces. The isolate was characterized by phylogenetic and phenotypic properties, as well as by determination of its whole genome sequence. The growth temperature and pH ranges were 30-42 °C and 6.0-8.5, respectively. The end products of glucose fermentation were butyric acid and a small amount of acetic acid. The genome was estimated to be 3.61 Mbp with G + C content of 36.8 mol%. Genes related to biosynthesis of diaminopimelic acid, polar lipids, polyamines, teichoic and lipoteichoic acids were present. The predominant fatty acids were C16:0 (37.9%), C14:0 (16.4%), C13:0 OH/iso-C15:1H (11.1%) and C18:1ω9c (10.6%). Phylogenetic analyses based on 16S rRNA gene sequences demonstrated that the isolate was a member of family Lachnospiraceae, with the highest sequence similarity to the type strain of Roseburia intestinalis DSM 14610T (92.2%), followed by Acetivibrio ethanolgignens ATCC 33324T (92.0%). The average nucleotide identity (ANI) and average amino acid identity (AAI) values between strain TF01-11T and these closest relatives were less than 70.5% and 52.3%. Based on results of phenotypic characteristics and genotypic properties presented in this study, strain TF01-11T represents a novel species in a new genus, for which the name Butyribacter intestini gen. nov., sp. nov. is proposed. The type strain of the type species is TF01-11T (CGMCC 1.5203T = DSM 105140T). In addition, Acetivibrio ethanolgignens is proposed to be reclassified as Acetanaerobacter ethanolgignens gen. nov., comb. nov.

Taxonomic Description and Genome Sequence of Christensenella intestinihominis sp. nov., a Novel Cholesterol-Lowering Bacterium Isolated From Human Gut.

A Gram-staining-negative, non-spore-forming, short, straight rod, non-motile, and obligate anaerobic bacterial strain, AF73-05CM02T, was isolated from a fecal sample of a 30 years old healthy male living in Shenzhen, China. Colonies were approximately 0.2 mm in diameter, beige, and circular after 4 days of incubation on PYG agar under anaerobic conditions at 37°C. Strain AF73-05CM02T grew in a temperature range between 30 and 42°C and a pH range from 6.0 to 8.5, with optimum growth at 37-42°C and pH 7.0. 16S rRNA gene sequence analysis demonstrated that strain AF73-05CM02T belongs to the genus Christensenella and showed the highest level of sequence similarity (98.68%) with Christensenella minuta DSM 22607T. The predominant fatty acids of strain AF73-05CM02T were C10 : 0 (7.5%), iso-C11 : 0 (5.6%), C12 : 0 (7.2%), C14 : 0 (46.6%), iso-C15 : 0 (7.4%), C16 : 0 (9.7%), and C18 : 1 ω9c (6.9%). Acetic acid, formic acid, butyric acid, and lactic acid were the end products of glucose fermentation. The strain was negative for catalase, indole production, and hydrolysis of gelatin. Genomic relatedness analyses based on average nucleotide identity (ANI) indicated that strain AF73-05CM02T significantly differed from other species of the genus Christensenella, showing ANI values less than 82.89% with the phylogenetically closest species. The G + C content of the genomic DNA was 52.07 mol% from the genome sequence, which differs from that of Christensenella minuta. Several physiological, biochemical, and genotypic properties differentiated the novel bacterial strain from the related species, indicating that the strain represents a new species of the genus Christensenella for which the name Christensenella intestinihominis sp. nov. is proposed, with strain AF73-05CM02T ( = CGMCC 1.5207T = DSM 103477T ) being the type strain. The following study explored the cholesterol-lowering function of strains AF73-05CM02T and Christensenella minuta DSM 22067T and revealed that the two strains exhibit the capacity for removing cholesterol with efficiency rates of 36.6 and 54.3% and produce exopolysaccharide of 234 and 271 mg/L, respectively.

Beilunmycin, a new virginiamycins antibiotic from mangrove-derived Streptomyces sp. 2BBP-J2 and the antibacterial activity by inhibiting protein translation.

One new virginiamycin derivative, 'beilunmycin' (1), and three known virginiamycin antibiotics, 16-hydroxy-virginiamycin M1 (2), virginiamycin M2 (3), and virginiamycin M1 (4), were isolated from the culture of a mangrove-derived endophytic Streptomyces sp. 2BBP-J2. The structures were characterized on the basis of their spectroscopic data, and the absolute configuration of 1 was established by ECD calculations. Compounds 1-4 exhibited antibacterial activities against Gram-positive bacteria, with MIC values in the range of 0.5-16 µg/ml. All the compounds demonstrated strong protein translation-stalling activity, with minimal concentrations detected with pDualrep2 in the range of 1.9-5.9 nmol.

Motilibacter deserti sp. nov. and Motilibacter aurantiacus sp. nov., two novel actinobacteria isolated from soil of Cholistan Desert and emended description of the genus Motilibacter.

Two novel actinobacterial strains, designated as E257T and K478T, were isolated from hyper-arid soil samples collected in Cholistan Desert, Pakistan. Comparative analysis of 16S rRNA genes showed that strains E257T and K478T were assigned to the genus Motilibacter, being their closest relative M. rhizosphaerae RS-16T with 97.3% and 96.7% similarities, respectively. The sequence similarity between strain E257T and K478T was 98.9%. Phylogenetic analysis based on 16S rRNA gene sequences and phylogenomic analysis based on multiple genes of conserved core proteins exhibited that these two strains belonged to the genus Motilibacter and formed a robust cluster separated from the two type species of the genus Motilibacter. Average Nucleotide Identity (ANI), Average Amino acid Identity (AAI), digital DNA-DNA hybridization (dDDH) values and Percentage of Conserved Proteins (POCP) calculated from the complete genome sequences indicated strains E257T and K478T were assigned into genus Motilibacter but clearly separated from each other and from the other species of the genus Motilibacter with values below the thresholds for species delineation. The two isolates were found to have chemotaxonomic, cultural and morphological properties consistent with their classification in the genus Motilibacter and also confirmed the differentiation from their closest species. The obtained results demonstrated that strains E257T and K478T represent two novel species of the genus Motilibacter, for which the names Motilibacter desertisp. nov. (type strain E257T = JCM 33651T = CGMCC 1.17159T) and Motilibacter aurantiacus sp. nov. (type strain K478T =JCM 33652T =CGMCC 1.17229T) are proposed.

Arthrobacter mobilis sp. nov., a novel actinobacterium isolated from Cholistan desert soil.

A Gram-stain-positive, aerobic, catalase-positive, oxidase-negative, non-mycelium-forming, motile, rod-shaped with one polar flagellum actinobacterium, designated E918T, was isolated from a desert soil collected in Cholistan desert, Pakistan. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain E918T belonged to the genus Arthrobacter and was most closely related to Arthrobacter deserti CGMCC 1.15091T (97.2 % similarity). The peptidoglycan was of the A3α type and the whole-cell sugar profile was found to contain galactose. The major menaquinone was MK-9(H2). The polar lipid profile consisted of diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol and two unidentified glycolipids. The major fatty acids identified were anteiso-C15 : 0 and anteiso-C17 : 0. The G+C content of the genomic DNA was 68.69 mol%. The digital DNA-DNA hybridization and average nucleotide identity values between strain E918T and A. deserti CGMCC 1.15091T were 28.0 and 83.4%, respectively. On the basis of its phylogenetic, phenotypic and chemotaxonomic features, strain E918T was considered to represent a novel species of the genus Arthrobacter, for which the name Arthrobacter mobilis sp. nov. is proposed. The type strain of Arthrobacter mobilis is E918T (=JCM 33392T=CGMCC 1.16978T).

Planctomonas psychrotolerans sp. nov., isolated from rhizosphere soil of Suaeda salsa.

A psychrotolerant actinobacterium, designated strain J5903T, was isolated from an alkaline soil sample from the rhizosphere of Suaeda salsa collected in desertification land surrounding Jiuliancheng Nur in Hebei Province, PR China. Cells of the isolate were Gram-stain-positive, aerobic, non-motile and non-spore-forming cocci. Strain J5903T grew optimally at 20‒25 °C, at pH 7.0‒7.5 and with <1 % (w/v) NaCl. The cell-wall peptidoglycan type was B2γ with d-2,4-diaminobutyric acid and l-2,4-diaminobutyric acid as diagnostic amino acids. The muramyl residue was acetyl type. The menaquinones were MK-11, MK-12, MK-10 and MK-13. The major polar lipids were diphosphatidylglycerol, phosphatidylglycerol and one unidentified glycolipid. The major whole-cell fatty acids were anteiso-C15 : 0, iso-C16 : 0 and anteiso-C17 : 0. The genomic DNA G+C content was 69.1 mol%. It shared the highest average nucleotide identity and digital DNA-DNA hybridization values with Planctomonas deserti 13S1-3T. Phylogenies based on genome sequence showed that strain J5903T and P. deserti 13S1-3T formed a robust cluster with high bootstrap support. Strain J5903T shared typical chemotaxonomic characteristics with P. deserti 13S1-3T. Combining the polyphasic taxonomic evidence, strain J5903T represents a novel species of the genus Planctomonas, for which the name Planctomonas psychrotolerans sp. nov. is proposed. The type strain is J5903T (=DSM 101894T=CGMCC 1.15523T).

Phytoactinopolyspora mesophila sp. nov., isolated from a saline-alkaline soil.

A novel moderately halophilic, filamentous actinobacterium, designated as XMNu-373T, was isolated from a saline-alkaline soil sample collected from the Mongolia Plateau, Dongwu County, Inner Mongolia Autonomous Region, PR China. The isolate grew optimally at 28‒37 °C, pH 7.0‒8.0 and with 2-5 % (w/v) NaCl. The substrate mycelia fragmented into rod-like elements, and the white aerial mycelia formed spore chains at maturity. The predominant menaquinone was MK-9(H4). The polar lipids were diphosphatidylglycerol, three unidentified phosphoglycolipids, an unidentified aminophospholipid, two phosphatidylinositol mannosides, four unidentified phospholipids, phosphatidylglycerol and two unidentified lipids. The major cellular fatty acids were iso-C16 : 0, anteiso-C17 : 0 and anteiso-C15 : 0. The genomic DNA G+C content was 66.2 mol%. It shared high 16S rRNA gene sequence similarities to Phytoactinopolyspora halotolerans YIM 96448T (96.1 %) and Phytoactinopolyspora endophytica EGI 60009T (96.0 %). Phylogenetic trees based on 16S rRNA gene sequences revealed that strain XMNu-373T resided in the clade of family Jiangellaceae, and it formed a monophyletic branch distinct from four other recognized type species in the subclade of the genus Phytoactinopolyspora. On the basis of polyphasic taxonomic evidence, strain XMNu-373T represents a novel species of the genus Phytoactinopolyspora, for which the name Phytoactinopolyspora mesophila sp. nov. is proposed. The type strain is XMNu-373T (=JCM 33740T=CGMCC 4.7654T).

Auraticoccus cholistanensis sp. nov., an actinomycete isolated from soil of the Cholistan Desert, and emended description of the genus Auraticoccus.

A Gram-stain-positive, aerobic, non-motile and non-spore-forming actinobacterium, designated as F435T, was isolated from soil sample collected from the Cholistan Desert, Pakistan. The taxonomic position of the strain was established by using a polyphasic taxonomic approach. The cells were coccoid-shaped and found in single or arrangement of pairs. The novel strain grew at 15‒37 °C (optimum, 25‒30 °C), pH 7‒11 (optimum, pH 7-8) and in the presence of 0‒8% (w/v) NaCl (optimum, 0 %). Results of blast analysis based on 16S rRNA gene sequences showed that Auraticoccus monumenti MON 2.2T was its closest relative with 97.4 % similarity followed by Desertihabitans aurantiacus CPCC 204711T (95.2 %). In phylogenetic trees, strain F435T formed a robust cluster with the only member of the genus Auraticoccus. The peptidoglycan isomer present in the cell wall was ll-diaminopimelic acid. The major fatty acid was determined to be anteiso-C15 : 0. Characteristic polar lipids of the strain were diphosphatidylglycerol, phosphatidylglycerol, phosphoglycolipids and glycolipids. The predominant menaquinone was MK-9(H4). The genomic G+C content was calculated as 73.5 mol%. The digital DNA-DNA hybridization (GGDC) and average nucleotide identity (ANI) values between strain F435T and A. monumenti MON 2.2T were 24.6 and 81.8 %, respectively. Based on the results of phenotypic, chemotaxonomic, phylogenetic and phylogenomic analyses, strain F435T represents a novel specie of the genus Auraticoccus, for which the name Auraticoccus cholistanensis sp. nov. is proposed. The type strain is F435T (=JCM 33648T=CGMCC 1.17443T). The description of the genus Auraticoccus has also been emended.

Nocardioides vastitatis sp. nov., isolated from Taklamakan desert soil.

A Gram-stain-positive, aerobic, non-motile, rod-shaped actinobacterium, designated strain 21Sc5-5T, was isolated from a soil sample collected in the Taklamakan desert in Xinjiang Uygur Autonomous Region, PR China and investigated by using a polyphasic approach. Strain 21Sc5-5T grew at 10-37 °C (optimum, 28-30 °C), pH 6.0-9.0 (optimum, pH 7.0) and in the presence of 0-3 % (w/v) NaCl (optimum, 0 %). Phylogenetic analysis based on 16S rRNA gene sequences suggested that strain 21Sc5-5T formed a distinct lineage within the genus Nocardioides and had the highest similarity to Nocardioides albidus THG-S11.7T (97.30 %), followed by Nocardioides kongjuensis A2-4T (97.22 %), Nocardioides nitrophenolicus NSP 41T (97.15 %) and Nocardioides caeni MN8T (97.15 %). The results of chemotaxonomic analyses showed that the isolate possessed ll-diaminopimelic acid as the diagnostic diamino acid of the peptidoglycan and MK-8(H4) as the predominant menaquinone. The polar lipids comprised diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol, an unidentified phospholipid and three unidentified lipids. The major fatty acids were iso-C16 : 0 and 10-methyl C18 : 0. The genome length of strain 21Sc5-5T was 4.67 Mb containing 372 contigs and with a DNA G+C content of 70.4 mol%. On the basis of data from phylogenetic, phenotypic and chemotaxonomic analyses, strain 21Sc5-5T represents a novel species of the genus Nocardioides, for which the name Nocardioides vastitatis sp. nov. is proposed. The type strain is 21Sc5-5T (=JCM 33365T=CGMCC 4.7608T).

Glycomyces buryatensis sp. nov., an actinobacterium isolated from steppe soil.

A novel actinobacterial strain, designated 18T, was isolated from a steppe soil sample collected in Buryatia, Russia and subjected to polyphasic taxonomic characterization. The strain was aerobic and Gram-stain-positive. The 16S rRNA gene sequence of strain 18T exhibited highest similarity to Glycomyces paridis CPCC 204357T (97.2 %). Results of phylogenetic analysis showed that strain 18T formed a distinct branch clearly affiliated to the genus Glycomyces. Whole-cell hydrolysates of the isolate contained meso-diaminopimelic acid as the cell-wall diamino acid. The whole-cell sugar profile was found to contain galactose, glucose, ribose and xylose. MK-10(H4) and MK-11(H4) were the predominant menaquinones. The polar lipid profile consisted of diphosphatidylglycerol, phosphatidylglycerol, five unidentified phospholipids and four unidentified polar lipids. The major fatty acids identified were anteiso-C15 : 0 and iso-C15 : 0. The G+C content of the genomic DNA of strain 18T was 68.0 mol% (draft genome sequence). Based on its phylogenetic, phenotypic and chemotaxonomic features, strain 18T was considered to represent a novel species of the genus Glycomyces, for which the name Glycomyces buryatensis sp. nov. is proposed. The type strain of Glycomyces buryatensis is 18T (=JCM 33362T=CGMCC 4.7610T).

Desertihabitans brevis sp. nov., an actinobacterium isolated from sand of the Taklamakan desert, and emended description of the genus Desertihabitans.

A novel actinobacterium, designated strain 16Sb5-5T, was isolated from a sand sample collected in the Taklamakan desert in Xinjiang Uygur Autonomous Region, China. The strain was examined by a polyphasic approach to clarify its taxonomic position. Cells of the isolate were Gram-staining-positive, aerobic, non-motile and short-rod shaped. Strain 16Sb5-5T grew optimally at 37 °C, pH 7.0 and with 0‒2 % (w/v) NaCl. The cell-wall peptidoglycan was of the A3γ type and contained alanine, glycine, glutamic acid and ll-diaminopimelic acid (ll-DAP). Ribose, arabinose and glucose were detected in the whole-cell hydrolysates. The predominant menaquinone was MK-9(H4). The polar lipid profile consisted of diphosphatidylglycerol, phosphatidylglycerol, phosphatidylcholine, an unidentified phospholipid, three unidentified glycolipids and three unidentified lipids. The major whole-cell fatty acids were anteiso-C15 : 0 and iso-C15 : 0. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain 16Sb5-5T was closely related to Desertihabitans aurantiacus CPCC 204711T (99.8 % similarity) and formed a robust clade with D. aurantiacus in the phylogenetic trees. In silico genomic comparisons showed that strain 16Sb5-5T exhibited ANI values of 94.8-94.9 % and GGDC value of 59.5 % to D. aurantiacus CPCC 204711T. The genomic G+C content was 73.3 mol%. On the basis of phylogenetic, phenotypic and chemotaxonomic analyses, strain 16Sb5-5T could be distinguishable from its closest phylogenetic relative and represents a novel species of the genus Desertihabitans, for which the name Desertihabitans brevis sp. nov. is proposed. The type strain is 16Sb5-5T (=KCTC 49116T=CGMCC 1.16553T). The description of the genus Desertihabitans has also been emended.

Exploitation of Potentially New Antibiotics from Mangrove Actinobacteria in Maowei Sea by Combination of Multiple Discovery Strategies.

Rediscovery of known antibiotics from actinobacteria, especially Streptomyces, has become a bottleneck issue. Nowadays, more specific identification and dereplication could be acquired by a combination of modern analytic techniques with various databases. In this study, 261 actinobacterial strains were isolated from 8 mangrove soil samples by culture-dependent method. A total of 83 strains were selected to evaluate antibacterial activities and mechanisms by disc diffusion method and a unique double fluorescent protein reporter system (pDualrep2), respectively. Thirty-two strains exhibited antagonistic activity against at least one of the "ESKAPE" pathogens. Four Streptomyces strains (B475, B486, B353, and B98) showed strong inhibitory activity against Gram-positive bacteria and induced DNA damage SOS response. One Micromonospora strain (B704) exhibited inhibitory activity against several pathogens and induced attenuation-based translational inhibitors reporter. Seven members of quinoxaline-type antibiotics including quinomycin A, quinomycin monosulfoxide, and other five putative new analogues were found from the culture broth of strain B475 by a combination of anti-MRSA guide, HPTLC, HPLC-UV, and UPLC-UV-HRESIMS/MS analysis, Chemspider searching, and MS/MS-based molecular networking analysis. In conclusion, this study not only demonstrated that mangrove is a rich source of actinobacteria with the potentially new antibiotics but showed rapid dereplication of known antibiotics in the early stage can improve efficiency for the discovery of new antibiotics.