Taxonomy of micromonospora strains from thai peat swamp forest soils and secondary metaboolites of a selected isolate

Abstract

In the course of our investigation for actinomycetes strains, fifty-two isolates which produced single non-motile spores were isolated from peat swamp forest soils in Trang, Pattaloong, Yala, and Narathiwat provinces. On the basis of the phenotypic and chemotaxonomic characteristics including the phylogenetic analysis using 16S rDNA sequences, they were identified as Micromonospora. The tested strains contained meso-diaminopimelic acid in cell wall (cell wall type II), xylose and arabinose as diagnostic whole-cell sugar pattern D, and phosphatidylethanolamine as characteristic phospholipid (type II). The major fatty acids of these strains were iso-C16:0, iso-C15:0, iso-C17:0, anteiso-C16:0, anteiso-C15:0, and anteiso-C17:0. Their major menaquinones were MK-9(H4), MK-9(H6), or MK-10(H4). The range of G+C content of the DNA was 71-73 mol%. Based on the DNA-DNA similarity and some physiological and biochemical properties, all strains could be separated into eleven groups. The following two groups could be identified as M. chalcea (Group I, 8 strains) and M. aurantiaca (Group III, 7 strains). A low level of DNA-DNA similarity (12.9-53.1%) and 16S rDNA similarity (97.5-99.2%) including the phenotypic characteristics of the remaining nine groups (Groups II, IV-XI, 37 strains) indicated that these groups readily distinguished from all of validly described Micromonospora species and should be recognized as the new species. In this study, the names Micromonospora eburnea sp. nov. and Micromonospora aurantionigra sp. nov. are proposed for Group VII (2 strains) and Group XI (1 strains), respectively. Micromonospora sp. TT1-11 was selected for secondary metabolite production since its ethylacetate crude extract showed significant antimicrobial activity. The ethyl acetate extract yielded a new polyene macrolide lactam (Micromonosporin A; 9,11,13-trihydroxy-14,19,24-trimethyl-1-azacyclotetracosa-3,5,7,15,17,19,21-heptaen-2-one). The hydrogenation reaction of this compound was performed and yielded 9,11,13-trihydroxy-14,19,24-trimethyl-1-azacyclotetracosan-2-one. The chemical structures of both compounds were elucidated through extensive analyses of their UV, IR, MS, and NMR spectroscopic data. Micromonosporin A was very unstable and has no antimicrobial activity. However, the derivative compound displayed weak antibacterial activity and also exhibited antimalarial activity at IC50 of 3.1 microgram/mL and antimycobacterial activity with the MIC of 50 microgram/mL.