Whole genome analysis of Streptomyces sp. RerS4, a Rehmannia glutinosa rhizosphere microbe producing a new lipopeptide.

Rehmannia glutinosa, a valuable medicinal plant, is threatened by ring rot, a condition that greatly affects its yield and quality. Interactions between plant and the rhizosphere soil microbiome in the context of pathogen invasion are generally more specific, with recruitment of specialized microbes potentially antagonistic to a certain pathogen. Isolation of microorganisms from rhizosphere soil of healthy and ring rot-infected R. glutinosa was carried out to screen antifungal microbes. A strain designated RerS4 isolated from ring rot-infected R. glutinosa rhizosphere soil with strong antifungal activities was selected for further study. RerS4 was taxonomically characterized as the genus Streptomyces according to its morphology and 16S rRNA sequences that were most closely related to Streptomyces racemochromogenes NRRL B-5430T (99.72%) and Streptomyces polychromogenes NBRC 13072T (99.72%). A new lipopeptide isolated from RerS4 showed restrained proliferation, but was devoid of significant antibacterial and antioxidant activity with minimum inhibitory concentration (MIC) values of 20.3 ± 2.5 and 70.8 ± 3.7 µg/mL and half-maximal inhibitory concentration (IC50) values of 23.3 ± 0.8 and 58.8 ± 2.9 µg/mL, respectively. In addition, we report the complete genome sequence of Streptomyces sp. RerS4, which consists of a 7,301,482 bp linear chromosome and a 242,139 bp plasmid. Genome analysis revealed that Streptomyces sp. RerS4 contained 25 biosynthetic gene clusters (BGCs) for secondary metabolites, among which 68% had low similarities with known BGCs, leading us to believe that Streptomyces sp. RerS4 could produce valuable bioactive compounds.

New milbemycin metabolites from the genetically engineered strain Streptomyces bingchenggensis BCJ60.

Two new milbemycin derivatives, 27-methoxylmilbemycin α31 (1) and 27-oxomilbemycin α31 (2), were isolated from the genetically engineered strain Streptomyces bingchenggensis BCJ60. Their structures were determined by 1D NMR, 2D NMR and HR-ESI-MS spectral analysis, and comparison with previous reports. The acaricidal and nematocidal capacities of compounds 1 and 2 were evaluated against Tetranychus cinnabarinus and Bursaphelenchus xylophilus, respectively. The results showed that the two new macrocyclic lactones 1 and 2 possessed potent acaricidal and nematocidal activities.

Mumia xiangluensis sp. nov., isolated from the rhizosphere of Peucedanum praeruptorum Dunn.

During an investigation of microbial diversity in medicinal herbs, a novel actinobacterium, strain NEAU-KD1(T) was isolated from the rhizosphere of Peucedanum praeruptorum Dunn collected from Xianglu Mountain in Heilongjiang Province, northeast China and characterized using a polyphasic approach. The organism was found to have the typical chemotaxonomic and morphological characteristics of the genus Mumia. Cells were observed to be non-spore-forming and irregular cocci. The cell wall was found to contain LL-diaminopimelic acid as the cell wall diamino acid. The whole-cell sugars were detected as galactose and rhamnose and the predominant menaquinone was identified as MK-9(H4). The polar lipids were found to consist of diphosphatidylglycerol, phosphatidylglycerol, phosphoglycolipid and five unidentified phospholipids. The major cellular fatty acids were determined to be composed of C16:0, 10-methyl C18:0 and C18:1ω7c. The phylogenetic analysis based on 16S rRNA gene sequence also indicated that strain NEAU-KD1(T) belongs to the genus Mumia and with high sequence similarity to Mumia flava NBRC 109973(T) (97.6 % sequence similarity). The results of DNA-DNA hybridization and the phenotypic characteristics indicated that strain NEAU-KD1(T) could be distinguished from its close phylogenetic relative. Thus, strain NEAU-KD1(T) can be concluded to represent a novel species of the genus Mumia, for which the name Mumia xiangluensis sp. nov. is proposed. The type strain is NEAU-KD1(T) (=CGMCC 4.7305(T) = DSM 101040(T)).