Herbidospora galbida sp. nov., a novel actinobacterium isolated from soil

Herbidomicins, two pairs of polyketide tautomers produced by an actinomycete of the genus Herbidospora

Herbidospora is one of the underexplored actinomycete genera from which only a limited number of secondary metabolites are reported. In our continuing investigation on less explored actinomycetes, a liquid culture of Herbidospora sp. RD 11066 was found to contain unknown metabolites that had no match in our in-house UV database. Chromatographic separation and following structural analysis using NMR and MS identified these metabolites to be chromanone and chromene derivatives, which were respectively composed of an inseparable mixture of two isomeric forms. The former polyketides, designated to be herbidomicins A1 (1) and A2 (2), are positional isomers in terms of a methyl substituent on an aromatic ring that mutually interconvert by acetal exchange by two phenolic hydroxy groups. The latter pair, herbidomicins B1 (3) and B2 (4), is Z/E-isomers regarding an enol ether double bond. Herbidomicins 1-4 were weakly antifungal against a dermatophytic fungus Trichophyton rubrum and were moderately cytotoxic against murine leukemia P388 cells.

Secondary Metabolites with Anti-Inflammatory Activities from an Actinobacteria Herbidospora daliensis

Bioassay-guided fractionation of extracts derived from solid cultures of a Herbidospora daliensis originating from Taiwan led to the isolation of five new compounds, for which we propose the name herbidosporadalins A−E (1−5), one isolated for the first time, herbidosporadalin F (6), together with two known compounds (7 & 8). Their structures were elucidated by spectroscopic analyses, including 1D- and 2D-NMR experiments with those of known analogues, and on the basis of HR-EI-MS mass spectrometry, their anti-inflammatory activities were also evaluated. Of these isolates, herbidosporadalin A (1), B (2), F (6) and G (8) showed NO inhibitory activity, with IC50 values of 11.8 ± 0.9, 7.1 ± 2.9, 17.8 ± 1.7, and 13.3 ± 6.5 μM, stronger than the positive control quercetin (IC50 = 36.8 ± 1.3 μM). To the best of our knowledge, this is the first report on 3,4-seco-friedelane metabolites (5, 6 & 8) from the genus Herbidospora.

Herbidospora solisilvae sp. nov., a novel cellulose-degrading actinobacterium isolated from forest soil

An aerobic, non-motile, Gram-stain positive, cellulose-degrading actinobacterium, designated strain NEAU-GS84^T, was isolated from a forest soil sample collected from Linchun Ridge Forest Park in Sanya, Hainan Province, China, and characterized using a polyphasic approach. Morphological and chemotaxonomic characteristics indicated that strain NEAU-GS84^T could belong to the genus Herbidospora. The 16S rRNA gene sequence analysis indeed confirmed that strain NEAU-GS84^T belonged to the genus Herbidospora and was most closely related to Herbidospora yilanensis JCM 18062^T (99.2% 16S rRNA gene sequence similarity) and Herbidospora galbida NEAU-GS14^T (99.0%). The cell wall of strain NEAU-GS84^T contained meso-diaminopimelic acid as the major diamino acid and the whole-cell hydrolysates mainly contained glucose, madurose and ribose. The major polar lipids were diphosphatidylglycerol, phosphatidylmethylethanolamine, phosphatidylethanolamine, hydroxyphosphatidylethanolamin, phosphoglycolipids, two phosphatidylinositol mannosides and one unidentified phospholipid. The predominant menaquinone was MK-10(H₄). Major fatty acids were 10-methly C_17:0, C_17:0 and iso-C_16:0. These chemotaxonomic data substantiated the affiliation of strain NEAU-GS84^T to the genus Herbidospora. The DNA G+C content was 70.7 mol%. The genome size of strain NEAU-GS84^T is about 8.37 Mb and contained 41 cellulose-binding domain synthesis genes, 13 β-glucosidase synthesis genes, 6 endoglucanase synthesis genes and 9 xylanase synthesis genes. Based on digital DNA-DNA hybridization and average nucleotide identity values, the new strain NEAU-GS84^T could be differentiated from its closest relatives. Therefore, the strain represents a novel species of the genus Herbidospora, for which the name Herbidospora solisilvae sp. nov. is proposed. The type strain is NEAU-GS84^T (= CCTCC AA 2018041^T = JCM 33460^T).