Fodinibacter luteus gen. nov., sp. nov., an actinobacterium isolated from a salt mine

Cave Actinobacteria as Producers of Bioactive Metabolites

Recently, there is an urgent need for new drugs due to the emergence of drug resistant pathogenic microorganisms and new infectious diseases. Members of phylum Actinobacteria are promising source of bioactive compounds notably antibiotics. The search for such new compounds has shifted to extreme or underexplored environments to increase the possibility of discovery. Cave ecosystems have attracted interest of the research community because of their unique characteristics and the microbiome residing inside including actinobacteria. At the time of writing, 47 species in 30 genera of actinobacteria were reported from cave and cave related habitats. Novel and promising bioactive compounds have been isolated and characterized. This mini-review focuses on the diversity of cultivable actinobacteria in cave and cave-related environments, and their bioactive metabolites from 1999 to 2018.

Monashia flava gen. nov., sp. nov., an actinobacterium of the family Intrasporangiaceae

A novel actinobacterial strain, MUSC 78^T, was isolated from a mangrove soil collected from Peninsular Malaysia. The taxonomic status of this strain was determined using a polyphasic approach. Comparative 16S rRNA gene sequence analysis revealed that strain MUSC 78^T represented a novel lineage within the class Actinobacteria. Strain MUSC 78^T formed a distinct clade in the family Intrasporangiaceae and was related most closely to members of the genera Terrabacter (98.3-96.8 % 16S rRNA gene sequence similarity), Intrasporangium (98.2-96.8 %), Humibacillus (97.2 %), Janibacter (97.0-95.3 %), Terracoccus (96.8 %), Kribbia (96.6 %), Phycicoccus (96.2-94.7 %), Knoellia (96.1-94.8 %), Tetrasphaera (96.0-94.9 %) and Lapillicoccus (95.9 %). Cells were irregular rod-shaped or cocci and stained Gram-positive. The cell-wall peptidoglycan type was A3γ, with ll-diaminopimelic acid as the diagnostic diamino acid. The main cell-wall sugar was mannose and lower amounts of galactose and rhamnose were present. The predominant menaquinone was MK-8(H₄). The polar lipid profile consisted of phosphatidylglycerol, phosphatidylinositol, phosphatidylethanolamine, diphosphatidylglycerol and phosphoglycolipid. The predominant fatty acids were iso-C_15 : 0, anteiso-C_15 : 0 and iso-C_16 : 0. The DNA G+C content was 73.1 mol%. Based on this polyphasic study, MUSC 78^T exhibited phylogenetic and phenotypic differences from members of the genera of the family Intrasporangiaceae, and therefore a novel species of a new genus, Monashia flava gen. nov., sp. nov., is proposed. The type strain of Monashia flava is MUSC 78^T ( = DSM 29621^T = MCCC 1K00454^T = NBRC 110749^T).

Oryzobacter terrae gen. nov., sp. nov., isolated from paddy soil

A bacterial strain, PSGM2-16(T), was isolated from a pot of paddy soil grown with rice in Suwon region, Republic of Korea, and was characterized as having aerobic, Gram-stain-positive, short-rod-shaped cells with one polar flagellum. The 16S rRNA gene sequence of strain PSGM2-16(T) revealed the highest sequence similarities with Knoellia locipacati DMZ1T (97.4%), Fodinibacter luteus YIM C003(T) (97.2%) and Lapillicoccus jejuensis R-Ac013(T) (97.0%), and the phylogenetic tree showed that strain PSGM2-16(T) formed a subgroup with Ornithinibacter aureus HB09001(T) and F. luteus YIM C003(T) within the family Intrasporangiaceae. The major fatty acids (>10% of the total fatty acids) of strain PSGM2-16(T) were iso-C16 : 0, C17 : 1ω8c and iso-C14 : 0. The predominant menaquinone was MK-8(H4). The polar lipids present were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol, three aminophospholipids and two phospholipids. The peptidoglycan was type A4γ with meso-diaminopimelic acid as the diagnostic diamino acid. DNA-DNA hybridization values between strain PSGM2-16(T) and closely related taxa were much less than 70%. The genomic DNA G+C content of strain PSGM2-16(T) was 70.0 mol%. On the basis of the evidence presented, it is concluded that strain PSGM2-16(T) represents a novel species of a new genus in the family Intrasporangiaceae, for which the name Oryzobacter terrae gen. nov., sp. nov. is proposed. The type strain of the type species is PSGM2-16(T) ( = KACC 17299(T)= DSM 27137(T)= NBRC 109598(T)).

Actinobacterial diversity in limestone deposit sites in Hundung, Manipur (India) and their antimicrobial activities

Studies on actinobacterial diversity in limestone habitats are scarce. This paper reports profiling of actinobacteria isolated from Hundung limestone samples in Manipur, India using ARDRA as the molecular tool for preliminary classification. A total of 137 actinobacteria were clustered into 31 phylotypic groups based on the ARDRA pattern generated and representative of each group was subjected to 16S rRNA gene sequencing. Generic diversity of the limestone isolates consisted of Streptomyces (15 phylotypic groups), Micromonospora (4), Amycolatopsis (3), Arthrobacter (3), Kitasatospora (2), Janibacter (1), Nocardia (1), Pseudonocardia (1) and Rhodococcus (1). Considering the antimicrobial potential of these actinobacteria, 19 showed antimicrobial activities against at least one of the bacterial and candidal test pathogens, while 45 exhibit biocontrol activities against at least one of the rice fungal pathogens. Out of the 137 actinobacterial isolates, 118 were found to have at least one of the three biosynthetic gene clusters (PKS-I, PKS-II, NRPS). The results indicate that 86% of the strains isolated from Hundung limestone deposit sites possessed biosynthetic gene clusters of which 40% exhibited antimicrobial activities. It can, therefore, be concluded that limestone habitat is a promising source for search of novel secondary metabolites.

Comparative molecular analysis of the prokaryotic diversity of two salt mine soils in southwest China

While much is known about the microbial diversity in some hypersaline environments, little is known about those of salt mine tunnel soils. The objective of this study was to conduct a comprehensive phylogenetic comparison of the archaeal and bacterial communities present in Yipinglang salt mine (YPL) and Qiaohou salt mine (QH) tunnels differing in salinity and salt composition using 16S rRNA gene clone libraries. Two hundred twenty-eight sequences for QH and 182 sequences for YPL were analyzed by amplified ribosomal DNA-restriction analysis. Libraries revealed 44 bacterial and 57 archaeal different operational taxonomic units belonging to at least 8 bacterial and 3 archaeal divisions, but not all divisions were observed in both salt mines. The bacterial community affiliated with the Bacteroidetes was the most abundant (60% of clones) in QH, while the community in YPL was dominated by δ-Proteobacteria (45% of clones). All archaeal clones from QH were affiliated with Halobacteriaceae. In contrast, in the YPL library, 49% of clones belonged to Halobacteriaceae, 31% of clones related to unclassified archaea, and 21% of clones belonged to Crenarchaeota. Bioinformatic analysis and comparisons showed that the clone libraries were significantly different between two salt mines.

Proposal of Intrasporangium mesophilum sp. nov., and reclassification of Humihabitans oryzae Kageyama et al. 2007 as Intrasporangium oryzae comb. nov

A Gram-positive and aerobic bacterium, designated strain YIM 49065T, was isolated from rhizospheric soil of Jatropha curcas in Yunnan, China. This isolate formed branched and fragmented mycelia containing ll-diaminopimelic acid as the diagnostic diamino acid in the cell-wall peptidoglycan. The major cellular fatty acid profile was characterized by iso-C14 : 0, iso-C15 : 0 and iso-C16 : 0, and the predominant menaquinone was MK-8(H4). The DNA G+C content was 69.6 mol%. A phylogenetic analysis based on 16S rRNA gene sequence demonstrated that strain YIM 49065T was closely associated with Intrasporangium calvum DSM 43043T and Humihabitans oryzae KV-657T, exhibiting 98.8 % and 98.6 % 16S rRNA gene sequence similarities, respectively. Furthermore, DNA–DNA hybridizations among strains YIM 49065T, I. calvum DSM 43043T and H. oryzae DSM 22331T indicated that this isolate represented a novel species in the genus Intrasporangium . On the basis of these data, we proposed one novel species, Intrasporangium mesophilum sp. nov., for strain YIM 49065T ( = DSM 23217T  = CCTCC AA 209077T). Additionally, the comparison of biochemical and phylogenetic characters supported the reclassification of Humihabitans oryzae as a separate species within the genus Intrasporangium , Intrasporangium oryzae comb. nov. (type strain KV-657T  = JCM 15924T  = NBRC 101802T  = NRRL B-24470T).

Knoellia flava sp. nov., isolated from pig manure

A Gram-positive, aerobic, non-spore-forming actinobacterial strain, designated strain TL1T, was isolated from pig manure in Wuhan, China. The cell wall peptidoglycan contained meso-diaminopimelic acid. The major polar lipids were phosphatidylethanolamine, phosphatidylinositol and diphosphatidylglycerol. The predominant menaquinone was MK-8(H4). The major fatty acids (>10 %) were iso-C16 : 0, iso-C15 : 0 and C17 : 1ω8c. The genomic DNA G+C content was 70.9 mol%. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain TL1T was most closely related to the type strains of Knoellia sinensis (98.5 %), Knoellia subterranea (98.2 %) and Knoellia aerolata (96.9 %). DNA–DNA relatedness values of strain TL1T with the type strains of K. sinensis and K. subterranea were 27.3 and 34.0 %, respectively. Comparison of phenotypic, chemotaxonomic and phylogenetic characteristics among strain TL1T and related organisms revealed that the isolate represents a novel species of the genus Knoellia, for which the name Knoellia flava sp. nov. is proposed; the type strain is TL1T ( = CGMCC 1.10749T = KCTC 19810T).

Ornithinibacter aureus gen. nov., sp. nov., a novel member of the family Intrasporangiaceae

A novel strain of the class Actinobacteria was isolated from a seawater sample collected in the South China Sea using modified R2A agar plates. The strain was a Gram-stain-positive, non-motile, non-spore-forming, catalase-positive, irregular rod-shaped bacterium. The strain grew at 4–45 °C and pH 5.0–10.2, and tolerated 5 % (w/v) NaCl. Based on its 16S rRNA gene sequence, the organism was related phylogenetically to members of the genera Fodinibacter (96.7 % similarity), Lapillicoccus (96.5 %), Knoellia (95.0–95.8 %), Oryzihumus (95.6 %) and Humibacillus (95.6 %). The cell-wall contained l-ornithine as the major diagnostic diamino acid in the peptidoglycan. MK-8(H4) was the predominant menaquinone. Major cellular fatty acids were iso-C18 : 1 ω9c, iso-C16 : 0, iso-C15 : 0 and C17 : 0. The G+C content of the DNA was 69.6 mol%. Phenotypic and phylogenetic data revealed that this strain represents a novel species in a new genus of the family Intrasporangiaceae, for which the name Ornithinibacter aureus gen. nov., sp. nov. is proposed; the type strain of Ornithinibacter aureus is HB09001T (=CGMCC 1.10341T =DSM 23364T).