Root Morphogenesis of Arabidopsis thaliana Tuned by Plant Growth-Promoting Streptomyces Isolated From Root-Associated Soil of Artemisia annua

In this study, the capacity to tune root morphogenesis by a plant growth-promoting rhizobacterium, Streptomyces lincolnensis L4, was investigated from various aspects including microbial physiology, root development, and root endophytic microbial community. Strain L4 was isolated from the root-associated soil of 7-year plantation of Artemisia annua. Aiming at revealing the promotion mechanism of Streptomyces on root growth and development, this study first evaluated the growth promotion characters of S. lincolnensis L4, followed by investigation in the effect of L4 inoculation on root morphology, endophytic microbiota of root system, and expression of genes involved in root development in Arabidopsis thaliana. Streptomyces lincolnensis L4 is able to hydrolyze organic and inorganic phosphorus, fix nitrogen, and produce IAA, ACC deaminase, and siderophore, which shaped specific structure of endophytic bacterial community with dominant Streptomyces in roots and promoted the development of roots. From the observation of root development characteristics, root length, root diameter, and the number of root hairs were increased by inoculation of strain L4, which were verified by the differential expression of root development-related genes in A. thaliana. Genomic traits of S. lincolnensis L4 which further revealed its capacity for plant growth promotion in which genes involved in phosphorus solubilization, ACC deamination, iron transportation, and IAA production were identified. This root growth-promoting strain has the potential to develop green method for regulating plant development. These findings provide us ecological knowledge of microenvironment around root system and a new approach for regulating root development.

Simultaneous Improvement of Lincomycin a Production and Reduction of Lincomycin B Levels in Streptomyces Lincolnensis Using a Combined Medium Optimization Approach

PurposeThe current study aimed to optimize the culture and production parameters of industrial production of lincomycin A by Streptomyces lincolnensis using a statistical approach that could also reduce unwanted by-products. MethodsThe Plackett-Burman design, steepest ascent method, and response surface design were used to evaluate different factors that affect lincomycin A production. ResultsUsing an optimized S. lincolnensis fermentation medium, lincomycin A production was increased up to 4600 mg/L in shaking flasks, which indicated a 28.3% improvement over previous production in an un-optimized medium (3585 mg/L). Additionally, the concentration of lincomycin B by-product was reduced to 0.8%, which was 82.2% lower than that in the un-optimized medium. Further, quantitative real-time PCR analysis revealed the optimized medium improved lincomycin A production by stimulating key genes in the lincomycin A biosynthesis pathway, as well as an osmotic stress gene. ConclusionsOptimizing the fermentation medium improved lincomycin A production and decreased that of the lincomycin B by-product, which could help cut production costs and simplify downstream separation processes. We found that osmotic stress reduced the concentration of lincomycin B, which could also help reduce fermentation by-product yields in other actinobacteria.

LmbU directly regulates SLINC_RS02575, SLINC_RS05540 and SLINC_RS42780, which are located outside the lmb cluster and inhibit lincomycin biosynthesis in Streptomyces lincolnensis

The productions of antibiotics are usually regulated by cluster-situated regulators (CSRs), which can directly regulate the genes within the corresponding biosynthetic gene cluster (BGC). However, few studies have looked into the regulation of CSRs on the targets outside the BGC. Here, we screened the targets of LmbU in the whole genome of S. lincolnensis, and found 14 candidate targets, among of which, 8 targets can bind to LmbU by EMSAs. Reporter assays in vivo revealed that LmbU repressed transcription of SLINC_RS02575 and SLINC_RS05540, while activated transcription of SLINC_RS42780. In addition, disruptions of SLINC_RS02575, SLINC_RS05540 and SLINC_RS42780 promoted the production of lincomycin, and qRT-PCR showed that SLINC_RS02575, SLINC_RS05540 and SLINC_RS42780 inhibited transcription of the lmb genes, indicating that all the three regulators can negatively regulate lincomycin biosynthesis. What's more, the homologues of LmbU and its targets SLINC_RS02575, SLINC_RS05540 and SLINC_RS42780 are widely found in actinomycetes, while the distributions of DNA-binding sites (DBS) of LmbU are diverse, indicating the regulatory mechanisms of LmbU homologues in various strains are different and complicated.

Isoishwarane synthase from Streptomyces lincolnensis

The product of a terpene synthase from Streptomyces lincolnensis has been identified as the new natural product isoishwarane. The enzyme mechanism was studied by isotopic labelling experiments and site-directed mutagenesis.

Streptomyces montanus sp. nov., a novel actinomycete isolated from soil

A novel actinomycete, designated strain NEAU-C151T, was isolated from soil collected from Mount Song and characterized using a polyphasic approach. Analysis of the 16S rRNA gene sequence indicated that strain NEAU-C151T belongs to the genus Streptomyces and exhibited 97.5, 97.4 and 97.4 % similarities to Streptomyces lincolnensis NRRL 2936T, Streptomyces coacervatus AS-0823T, and Streptomyces longisporus ISP 5166T, respectively. The assignment of strain NEAU-C151T to the genus Streptomyces was confirmed by chemotaxonomic data: anteiso-C15 : 0, C16 : 0, iso-C16 : 0, C16 : 1 (ω7c) and anteiso-C17 : 0 as the major cellular fatty acids; whole-cell sugars contained ribose and glucose; phospholipid profile consisted of diphosphatidylglycerol (DPG), phosphatidylethanolamine (PE), unidentified phospholipid (PL), unidentified lipids (L) and phosphatidylinositol mannoside (PIM); the menaquinones were MK-9(H4), MK-9(H6), MK-10(H2) and MK-9(H8). However, multilocus sequence analysis based on five other house-keeping genes (atpD, gyrB, recA, rpoB, and trpB), DNA–DNA relatedness and phenotypic data showed that strain NEAU-C151T could be distinguished from its closest relatives. Consequently, strain NEAU-C151T represents a novel species of the genus Streptomyces , for which the name Streptomyces montanus sp. nov. is proposed. The type strain is NEAU-C151T (=CGMCC 4.7498T=DSM 107808T).

Comparative transcriptomic analysis reveals the significant pleiotropic regulatory effects of LmbU on lincomycin biosynthesis

Background Lincomycin, produced by Streptomyces lincolnensis, is a lincosamide antibiotic and widely used for the treatment of the infective diseases caused by Gram-positive bacteria. The mechanisms of lincomycin biosynthesis have been deeply explored in recent years. However, the regulatory effects of LmbU that is a transcriptional regulator in lincomycin biosynthetic (lmb) gene cluster have not been fully addressed. Results LmbU was used to search for homologous LmbU (LmbU-like) proteins in the genomes of actinobacteria, and the results showed that LmbU-like proteins are highly distributed regulators in the biosynthetic gene clusters (BGCs) of secondary metabolites or/and out of the BGCs in actinomycetes. The overexpression, inactivation and complementation of the lmbU gene indicated that LmbU positively controls lincomycin biosynthesis in S. lincolnensis. Comparative transcriptomic analysis further revealed that LmbU activates the 28 lmb genes at whole lmb cluster manner. Furthermore, LmbU represses the transcription of the non-lmb gene hpdA in the biosynthesis of l-tyrosine, the precursor of lincomycin. LmbU up-regulates nineteen non-lmb genes, which would be involved in multi-drug flux to self-resistance, nitrate and sugar transmembrane transport and utilization, and redox metabolisms. Conclusions LmbU is a significant pleiotropic transcriptional regulator in lincomycin biosynthesis by entirely activating the lmb cluster and regulating the non-lmb genes in Streptomyces lincolnensis. Our results first revealed the pleiotropic regulatory function of LmbU, and shed new light on the transcriptional effects of LmbU-like family proteins on antibiotic biosynthesis in actinomycetes.