Micromonospora maritima sp. nov., isolated from mangrove soil

Biotechnological and Ecological Potential of Micromonospora provocatoris sp. nov., a Gifted Strain Isolated from the Challenger Deep of the Mariana Trench

A Micromonospora strain, isolate MT25^T, was recovered from a sediment collected from the Challenger Deep of the Mariana Trench using a selective isolation procedure. The isolate produced two major metabolites, n-acetylglutaminyl glutamine amide and desferrioxamine B, the chemical structures of which were determined using 1D and 2D-NMR, including ¹H-¹⁵N HSQC and ¹H-¹⁵N HMBC 2D-NMR, as well as high resolution MS. A whole genome sequence of the strain showed the presence of ten natural product-biosynthetic gene clusters, including one responsible for the biosynthesis of desferrioxamine B. Whilst 16S rRNA gene sequence analyses showed that the isolate was most closely related to the type strain of Micromonospora chalcea, a whole genome sequence analysis revealed it to be most closely related to Micromonospora tulbaghiae 45142^T. The two strains were distinguished using a combination of genomic and phenotypic features. Based on these data, it is proposed that strain MT25^T (NCIMB 15245^T, TISTR 2834^T) be classified as Micromonospora provocatoris sp. nov. Analysis of the genome sequence of strain MT25^T (genome size 6.1 Mbp) revealed genes predicted to responsible for its adaptation to extreme environmental conditions that prevail in deep-sea sediments.

Bioactive Metabolites From Acid-Tolerant Fungi in a Thai Mangrove Sediment

Despite being potentially useful extremophile resources, there have been few reports on acid-tolerant fungi and their bioactive metabolites. Acidophilic/aciduric fungi (n = 237) were isolated from Thai mangrove sediments in an acidic medium. Using fungal identification technology (including morphologic observation, chemical screening, and sequence comparisons) all the isolates were identified and 41 representative isolates were selected for analysis of the phylogenetic relationships (ITS rDNA, β-tubulin, calmodulin, and actin gene sequences). There were seven genera identified – Penicillium; Aspergillus; Talaromyces; Cladosporium; Allophoma; Alternaria; and Trichoderma – in four taxonomic orders of the phylum Ascomycota, and Penicillium, Aspergillus, and Talaromyces were the dominant genera. Acidity tolerance was evaluated and 95% of the isolates could grow under extremely acidic conditions (pH 2). Six strains were classed as acidophilic fungi that cannot survive under pH 7, all of which had an extraordinarily close genetic relationship and belonged to the genus Talaromyces. This is the first report on the acidophilic characteristics of this genus. The antimicrobial, anti-tumor, and antiviral activities of the fermentation extracts were evaluated. Nearly three-quarters of the extracts showed cytotoxic activity, while less than a quarter showed antimicrobial or anti-H1N1 activity. The typical aciduric fungus Penicillium oxalicum OUCMDZ-5207 showed similar growth but completely different chemical diversity at pH 3 and 7. The metabolites of OUCMDZ-5207 that were obtained only at pH 3 were identified as tetrahydroauroglaucin (1), flavoglaucin (2), and auroglaucin (3), among which auroglaucin showed strong selective inhibition of A549 cells with an IC₅₀ value of 5.67 μM. These results suggest that acid stress can activate silent gene clusters to expand the diversity of secondary metabolites, and the bioprospecting of aciduric/acidophilic microorganism resources in Thai mangrove sediments may lead to the discovery of compounds with potential medicinal applications.

Micromonospora zhangzhouensis sp. nov., a Novel Actinobacterium Isolated from Mangrove Soil, Exerts a Cytotoxic Activity in vitro

A new bacterial strain, designated HM134^T, was isolated from a sample of soil collected from a Chinese mangrove Avicennia marina forest. Assessed by a polyphasic approach, the taxonomy of strain HM134^T was found to be associated with a range of phylogenetic and chemotaxonomic properties consistent with the genus Micromonospora. Phylogenetic analysis based on the 16s rRNA gene sequence indicated that strain HM134^T formed a distinct lineage with the most closely related species, including M. rifamycinica AM105^T, M. wenchangensis CCTCC AA 2012002^T and M. mangrovi 2803GPT1-18^T. The ANI values between strain HM134^T and the reference strains ranged from 82.6% to 95.2%, which was below the standard criteria for classifying strains as the same species (96.5%). Strain HM134^T and related species shared in silico dDDH similarities values below the recommended 70% cut-off for the delineation of species (range from 25.7–62.6%). The DNA G+C content of strain HM134^T was 73.2 mol%. Analysis of phylogenetic, genomic, phenotypic and chemotaxonomic characteristics revealed that strain HM134^T is considered to represent a novel species of the genus Micromonospora, for which the name M. zhangzhouensis sp. nov. is proposed. The extract of strain HM134^T was demonstrated to exhibit cytotoxic activity against the human cancer cell lines HepG2, HCT-116 and A549. Active substance presented in the fermentation broth of strain HM134^T was isolated by bioassay-guided analysis and purified afterwards. A new derivative of diterpenoid was identified through electrospray ionizing mass spectrometry (MS) and nuclear magnetic resonance (NMR). The compound showed different cytotoxic activities against cancer cells, with the highest cytotoxicity against HCT-116, corresponding to IC₅₀ value of 38.4 μg/mL.

Three New Isoflavonoid Glycosides from the Mangrove-Derived Actinomycete Micromonospora aurantiaca 110B

The mangrove ecosystem is a rich resource for the discovery of actinomycetes with potential applications in pharmaceutical science. Besides the genus Streptomyces, Micromonospora is also a source of new bioactive agents. We screened Micromonospora from the rhizosphere soil of mangrove plants in Fujian province, China, and 51 strains were obtained. Among them, the extracts of 12 isolates inhibited the growth of human lung carcinoma A549 cells. Strain 110B exhibited better cytotoxic activity, and its bioactive constituents were investigated. Consequently, three new isoflavonoid glycosides, daidzein-4'-(2-deoxy-α-l-fucopyranoside) (1), daidzein-7-(2-deoxy-α-l-fucopyranoside) (2), and daidzein-4',7-di-(2-deoxy-α-l-fucopyranoside) (3) were isolated from the fermentation broth of strain 110B. The structures of the new compounds were determined by spectroscopic methods, including 1D and 2D nuclear magnetic resonance (NMR) and high-resolution electrospray ionization mass spectrometry (HR-ESIMS). The result of medium-changing experiments implicated that these new compounds were microbial biotransformation products of strain M. aurantiaca 110B. The three compounds displayed moderate cytotoxic activity to the human lung carcinoma cell line A549, hepatocellular liver carcinoma cell line HepG2, and the human colon tumor cell line HCT116, whereas none of them showed antifungal or antibacterial activities.

Micromonospora yasonensis sp. nov., isolated from a Black Sea sediment

A Micromonospora strain, designated DS3186(T), isolated from sediment collected from the Black Sea off the Yason Peninsula, Ordu, Turkey, was examinated using a polyphasic approach. The strain was found to have chemotaxonomic, morphological and phylogenetic properties consistent with its clasification in the genus Micromonospora. A comparative 16S rRNA gene sequence analysis showed that the strain was closely related to the type strains of Micromonospora olivasterospora (99.0 %), Micromonospora equina (98.8 %), Micromonospora rhizosphaerae (98.8 %) and Micromonospora viridifaciens (98.8 %); low levels of DNA-DNA relatednes were found between the isolate and the M. olivasterospora and M. rhizosphaerae strains. Corresponding phylogenetic analysis based on partial gyrB gene sequences showed that strain DS3186(T) formed a subclade with the type strains of Micromonospora eburnea, M. equina, Micromonospora narathiwatensis and M. viridifaciens. Strain DS3186(T) was distinguished from its close phylogenetic neighbours using a combination of chemotaxonomic, morphological and physiological properties. Consequently, it is proposed that strain DS3186(T) represents a novel Micromonospora species for which the name Micromonospora yasonensis sp. nov. is proposed. The type strain is DS3186(T) (=DSM 45980(T) = KCTC 29433(T)).

Micromonospora mangrovi sp. nov., isolated from mangrove soil

A novel actinomycete strain 2803GPT1-18(T) was isolated from a composite mangrove soil sample collected from Beihai, Guangxi province, China. Phylogenetic analysis of the 16S rRNA gene sequence of strain 2803GPT1-18(T) indicated high similarity with 'Micromonospora harpali' NEAU-JC6(T) (99.2 %), Micromonospora haikouensis 232617(T) (99.1 %), Micromonospora wenchangensis 2602GPT1-05(T) (99.1 %), Micromonospora schwarzwaldensis HKI0641(T) (99.1 %). The gyrB gene sequence analysis also indicated that strain 2803GPT1-18(T) should be assigned to the genus Micromonospora but different from any established Micromonospora species. The strain harbored meso-DAP and glycine as major cell wall amino acids, MK-10(H6) (53.5 %), MK-9(H6) (25.1 %) and MK-9(H4) (13.4 %) as predominant menaquinones. The characteristic whole cell sugars are arabinose, xylose, glucose, galactose and mannose. The polar lipid profile comprises phosphatidylethanolamine, diphosphatidylglycerol, phosphatidylinositol and unidentified polar lipids. The major cellular fatty acids present are iso-C16:0 (44.2 %) and iso-C15:0 (12.4 %). The DNA G+C content is 71.2 mol%. Furthermore, a combination of DNA-DNA relatedness and some physiological and biochemical properties indicated that the novel strain could be readily distinguished from the closely related species. On the basis of these phenotypic and genotypic data, strain 2803GPT1-18(T) represents a novel species of the genus Micromonospora, for which the name Micromonospora mangrovi sp. nov. is proposed. The type strain is 2803GPT1-18(T) (=CCTCC AA2012012(T) = DSM45761(T)).

Micromonospora zhanjiangensis sp. nov., isolated from mangrove forest soil

A novel actinomycete, designated strain 2902at01T was isolated from soil collected at a mangrove forest in Zhanjiang, Guangdong province, China. The strain was identified using a polyphasic classification method. The 16S rRNA gene sequence of strain 2902at01T showed the highest similarity to Micromonospora equina Y22T (98.3 %) and Micromonospora pattaloongensis TJ2-2T (98.1 %). Phylogenetic analysis based on the gyrB gene sequence also clearly showed that the strain was different from any previously discovered species of the genus Micromonospora. The characteristic whole-cell sugars were ribose and xylose. The cell-wall hydrolysates contained alanine, asparagine, glycine and meso-diaminopimelic acid. MK-10(H6) and MK-10(H8) were the major menaquinones of the novel strain. The predominant fatty acids were iso-C15 : 0, anteiso-C15 : 0 and iso-C16 : 0. The characteristic polar lipids of strain 2902at01T were phosphatidylethanolamine, phosphatidylinositol, phosphatidylinositol mannoside and diphosphatidylglycerol. The DNA G+C content was 70.2 mol%. DNA–DNA hybridization data combined with other physiological and biochemical features could distinguish strain 2902at01T from the reference strains M. equina Y22T and M. pattaloongensis TJ2-2 T. On the basis of these phenotypic and genotypic data, strain 2902at01T represents a novel species of the genus Micromonospora, for which the name Micromonospora zhanjiangensis sp. nov. is proposed. The type strain is 2902at01T ( = CCTCC AA2014018T = DSM 45902T).

Mangrove rare actinobacteria: taxonomy, natural compound, and discovery of bioactivity

Actinobacteria are one of the most important and efficient groups of natural metabolite producers. The genus Streptomyces have been recognized as prolific producers of useful natural compounds as they produced more than half of the naturally-occurring antibiotics isolated to-date and continue as the primary source of new bioactive compounds. Lately, Streptomyces groups isolated from different environments produced the same types of compound, possibly due to frequent genetic exchanges between species. As a result, there is a dramatic increase in demand to look for new compounds which have pharmacological properties from another group of Actinobacteria, known as rare actinobacteria; which is isolated from special environments such as mangrove. Recently, mangrove ecosystem is becoming a hot spot for studies of bioactivities and the discovery of natural products. Many novel compounds discovered from the novel rare actinobacteria have been proven as potential new drugs in medical and pharmaceutical industries such as antibiotics, antimicrobials, antibacterials, anticancer, and antifungals. This review article highlights the latest studies on the discovery of natural compounds from the novel mangrove rare actinobacteria and provides insight on the impact of these findings.

Diaza-anthracene Antibiotics from a Freshwater-Derived Actinomycete with Selective Antibacterial Activity toward Mycobacterium tuberculosis

Multidrug- and extensively drug-resistant strains of Mycobacterium tuberculosis are resistant to first- and second-line drug regimens and resulted in 210,000 fatalities in 2013. In the current study, we screened a library of aquatic bacterial natural product fractions for their ability to inhibit this pathogen. A fraction from a Lake Michigan bacterium exhibited significant inhibitory activity, from which we characterized novel diazaquinomycins H and J. This antibiotic class displayed an in vitro activity profile similar or superior to clinically used anti-tuberculosis agents and maintained this potency against a panel of drug-resistant M. tuberculosis strains. Importantly, these are among the only freshwater-derived actinomycete bacterial metabolites described to date. Further in vitro profiling against a broad panel of bacteria indicated that this antibiotic class selectively targets M. tuberculosis. Additionally, in the case of this pathogen we present evidence counter to previous reports that claim the diazaquinomycins target thymidylate synthase in Gram-positive bacteria. Thus, we establish freshwater environments as potential sources for novel antibiotic leads and present the diazaquinomycins as potent and selective inhibitors of M. tuberculosis.

Micromonospora wenchangensis sp. nov., isolated from mangrove soil

An actinomycete, strain 2602GPT1-05(T), was isolated from a composite mangrove soil sample collected from Wenchang, Hainan province, China. Strain 2602GPT1-05(T) showed closest 16S rRNA gene sequence similarity to Micromonospora haikouensis 232617(T) (99.05 %), and phylogenetically clustered with Micromonospora haikouensis 232617(T), Micromonospora matsumotoense IMSNU 22003(T) (98.7 %) and Micromonospora rifamycinica AM105(T) (98.6 %) based on the 16S rRNA and gyrB gene sequence phylogenetic analysis. The strain harboured meso-DAP and glycine as major cell-wall amino acids, and MK-10(H6) and MK-9(H6) as predominant menaquinones. The characteristic whole-cell sugars were xylose, arabinose, glucose and galactose. The polar lipid profile comprised phosphatidylethanolamine, diphosphatidylglycerol, phosphatidylinositol, phosphatidylglycerol, phosphatidylinositol mannosides, unknown phospholipid and an unknown phosphoglycolipid. The major cellular fatty acids were C18 : 1ω9c, iso-C15 : 0, 10-methyl C18 : 0 (tuberculostearic acid), C16 : 0, C18 : 0 and iso-C16 : 0. The DNA G+C content was 71.7 mol%. Furthermore, some physiological and biochemical properties and low DNA-DNA relatedness values enabled the strain to be differentiated from members of closely related species. On the basis of these phenotypic, genotypic and chemotaxonomic data, strain 2602GPT1-05(T) represents a novel species of the genus Micromonospora, for which the name Micromonospora wenchangensis sp. nov. is proposed. The type strain is 2602GPT1-05(T) ( = CCTCC AA 2012002(T) = DSM 45709(T)).

Micromonospora sonneratiae sp. nov., isolated from a root of Sonneratia apetala

A novel endophytic actinomycete, strain 274745(T), was isolated from a root of Sonneratia apetala collected in a mangrove forest in Sanya, Hainan province, China. The 16S rRNA gene sequence of strain 274745(T) showed the greatest similarity to Micromonospora pattaloongensis TJ2-2(T) (98.3 %). Phylogenetic analysis based on the gyrB gene also supported the close relationship of these two strains. The predominant menaquinone was MK-10(H8) and the major fatty acids were iso-C15 : 0, C17 : 0 and anteiso-C15 : 0. The characteristic whole-cell sugars were xylose and mannose. The cell wall contained meso-diaminopimelic acid and glycine. The polar lipid profile mainly comprised phosphatidylethanolamine, phosphatidylinositol and diphosphatidylglycerol. The DNA G+C content was 71.6 mol%. Furthermore, a combination of DNA-DNA relatedness and some physiological and biochemical properties indicated that the novel strain could be readily distinguished from the closest phylogenetic relatives. On the basis of these phenotypic and genotypic data, strain 274745(T) represents a novel species of the genus Micromonospora, for which the name Micromonospora sonneratiae sp. nov. is proposed. The type strain is 274745(T) ( = CCTCC AA 2012003(T) = DSM 45704(T)).