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).

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.

Planctomonas deserti gen. nov., sp. nov., a new member of the family Microbacteriaceae isolated from soil of the Taklamakan desert.

A Gram-staining-positive, aerobic, irregular coccoid- to ovoid-shaped, non-spore-forming and motile bacterium, designated strain 13S1-3T, was isolated from a soil sample from the rhizosphere of Tamarix collected in the Taklamakan desert in Xinjiang Uygur Autonomous Region, PR China. The strain was examined by a polyphasic approach to clarify its taxonomic position. Strain 13S1-3T grew optimally at 28-30 °C, pH 7.0 and with 0-1 % (w/v) NaCl. The cell-wall peptidoglycan was of the B2γ type and contained d-alanine, d-glutamic acid, glycine, d-2,4-diaminobutyric acid and l-2,4-diaminobutyric acid. Ribose, xylose, glucose and galactose were detected as cell-wall sugars. The acyl type of the muramic acid was acetyl. The predominant menaquinones were MK-12, MK-11, MK-13 and MK-10. The major polar lipids were diphosphatidylglycerol, phosphatidylglycerol, two unidentified glycolipids and one unidentified phospholipid. The major whole-cell fatty acids were anteiso-C15 : 0, anteiso-C17 : 0 and iso-C16 : 0. The DNA G+C content was 70.4 mol%. Phylogenetic analysis based on 16S rRNA gene sequences indicated that 13S1-3T represented a member of the family Microbacteriaceae and showed the highest level of 16S rRNA gene sequence similarity with Frondihabitans australicus E1HC-02T (97.11 %). Phylogenetic trees revealed that 13S1-3T formed a distinct lineage with respect to closely related genera within the family Microbacteriaceae. On the basis of the results of phylogenetic, phenotypic and chemotaxonomic analyses, 13S1-3T is distinguishable from phylogenetically related genera in the family Microbacteriaceae, and represents a novel species of a new genus, for which the name Planctomonas deserti gen. nov., sp. nov. is proposed. The type strain is 13S1-3T (=KCTC 49115T=CGMCC 1.16554T).

Description of Salilacibacter albus gen. nov., sp. nov., isolated from a dried salt lake, and reclassification of Paraglycomyces xinjiangensis Luo et al. 2015 as a later heterotypic synonym of Salininema proteolyticum Nikou et al. 2015 with emended descriptions of the genus Salininema and Salininema proteolyticum.

A novel halophilic actinomycete, designated strain J11Y309T, was isolated from a soil sample collected from a dried salt lake in China. This isolate grew optimally at 28‒37 °C, with 3‒5 % (w/v) NaCl and at pH 7.0‒7.5. It contained meso-diaminopimelic acid as the diagnostic diamino acid and glucose, ribose and xylose were present in the whole-cell hydrolysates. MK-10(H4) was detected as the predominant menaquinone. The major fatty acids were anteiso-C17 : 0, iso-C16 : 0, iso-C17 : 0 and iso-C15 : 0. Polar lipids were phosphatidylethanolamine, phosphatidylglycerol, diphosphatidylglycerol, phosphatidylinositol, phosphatidylinositol mannoside, phosphoglycolipids, glycolipids, an unidentified phospholipid and additional unidentified lipids. The G+C content of the genomic DNA was 63.0 mol%. The novel strain shared highest 16S rRNA gene sequence similarity with Salininema proteolyticum Miq-4T (95.80 %), Paraglycomyces xinjiangensis TRM 49201T (95.77 %) and Haloglycomyces albus YIM 92370T (94.84 %). Phylogenetic trees showed that it could not be clearly assigned to any known genus within the family Glycomycetaceae and formed a distinct phylogenetic line in the clade comprising members of the genera Salininema, Paraglycomyces and Haloglycomyces. Based on data from the present polyphasic taxonomic study, strain J11Y309T represents a novel species of a new genus in the family Glycomycetaceae, for which the name Salilacibacter albus gen. nov., sp. nov. is proposed with Salilacibacter albus sp. nov. as the type species. The type strain of Salilacibacter albus is J11Y309T (=DSM 46875T=CGMCC 4.7242T=LMG 29297T). Reclassification of Paraglycomyces xinjiangensis Luo et al. 2015 as a later heterotypic synonym of Salininema roteolyticum Nikou et al. 2015 is also discussed in this study.

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.

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.

Diversity, Novelty, and Antimicrobial Activity of Endophytic Actinobacteria From Mangrove Plants in Beilun Estuary National Nature Reserve of Guangxi, China.

Endophytic actinobacteria are one of the important pharmaceutical resources and well known for producing different types of bioactive substances. Nevertheless, detection of the novelty, diversity, and bioactivity on endophytic actinobacteria isolated from mangrove plants are scarce. In this study, five different mangrove plants, Avicennia marina, Aegiceras corniculatum, Kandelia obovota, Bruguiera gymnorrhiza, and Thespesia populnea, were collected from Beilun Estuary National Nature Reserve in Guangxi Zhuang Autonomous Region, China. A total of 101 endophytic actinobacteria strains were recovered by culture-based approaches. They distributed in 7 orders, 15 families, and 28 genera including Streptomyces, Curtobacterium, Mycobacterium, Micrococcus, Brevibacterium, Kocuria, Nocardioides, Kineococcus, Kytococcus, Marmoricola, Microbacterium, Micromonospora, Actinoplanes, Agrococcus, Amnibacterium, Brachybacterium, Citricoccus, Dermacoccus, Glutamicibacter, Gordonia, Isoptericola, Janibacter, Leucobacter, Nocardia, Nocardiopsis, Pseudokineococcus, Sanguibacter, and Verrucosispora. Among them, seven strains were potentially new species of genera Nocardioides, Streptomyces, Amnibacterium, Marmoricola, and Mycobacterium. Above all, strain 8BXZ-J1 has already been characterized as a new species of the genus Marmoricola. A total of 63 out of 101 strains were chosen to screen antibacterial activities by paper-disk diffusion method and inhibitors of ribosome and DNA biosynthesis by means of a double fluorescent protein reporter. A total of 31 strains exhibited positive results in at least one antibacterial assay. Notably, strain 8BXZ-J1 and three other potential novel species, 7BMP-1, 5BQP-J3, and 1BXZ-J1, all showed antibacterial bioactivity. In addition, 21 strains showed inhibitory activities against at least one "ESKAPE" resistant pathogens. We also found that Streptomyces strains 2BBP-J2 and 1BBP-1 produce bioactive compound with inhibitory activity on protein biosynthesis as result of translation stalling. Meanwhile, Streptomyces strain 3BQP-1 produces bioactive compound inducing SOS-response due to DNA damage. In conclusion, this study proved mangrove plants harbored a high diversity of cultivable endophytic actinobacteria, which can be a promising source for discovery of novel species and bioactive compounds.