Streptomycetes from the rhizospheric soils are a rich resource of novel secondary metabolites with various biological activities. However, there is still little information related to the isolation, antimicrobial activity and biosynthetic potential for polyketide and non-ribosomal peptide discovery associated with the rhizospheric streptomycetes of Panax notoginseng. Thus, the aims of the present study are to (i) identify culturable streptomycetes from the rhizospheric soil of P. notoginseng by 16S rRNA gene, (ii) evaluate the antimicrobial activities of isolates and analyze the biosynthetic gene encoding polyketide synthases (PKSs) and nonribosomal peptide synthetases (NRPSs) of isolates, (iii) detect the bioactive secondary metabolites from selected streptomycetes, (iv) study the influence of the selected isolate on the growth of P. notoginseng in the continuous cropping field. This study would provide a preliminary basis for the further discovery of the secondary metabolites from streptomycetes isolated from the rhizospheric soil of P. notoginseng and their further utilization for biocontrol of plants. A total of 42 strains representing 42 species of the genus Streptomyces were isolated from 12 rhizospheric soil samples in the cultivation field of P. notoginseng and were analyzed by 16S rRNA gene sequencing. Overall, 40 crude cell extracts out of 42 under two culture conditions showed antibacterial and antifungal activities. Also, the presence of biosynthesis genes encoding type I and II polyketide synthase (PKS I and PKS II) and nonribosomal peptide synthetases (NRPSs) in 42 strains were established. Based on characteristic chemical profiles screening by High Performance Liquid Chromatography-Diode Array Detector (HPLC-DAD), the secondary metabolite profiles of strain SYP-A7257 were evaluated by High Performance Liquid Chromatography-High Resolution Mass Spectrometry (HPLC-HRMS). Finally, four compounds actinomycin X2 (F1), fungichromin (F2), thailandin B (F7) and antifungalmycin (F8) were isolated from strain SYP-A7257 by using chromatography techniques, UV, HR-ESI-MS and NMR, and their antimicrobial activities against the test bacteria and fungus were also evaluated. In the farm experiments, Streptomyces sp. SYP-A7257 showed healthy growth promotion and survival rate improvement of P. notoginseng in the continuous cropping field. We demonstrated the P. notoginseng rhizospheric soil-derived Streptomyces spp. distribution and diversity with respect to their metabolic potential for polyketides and non-ribosomal peptides, as well as the presence of biosynthesis genes PKS I, PKS II and NRPSs. Our results showed that cultivatable Streptomyces isolates from the rhizospheric soils of P. notoginseng have the ability to produce bioactive secondary metabolites. The farm experiments suggested that the rhizospheric soil Streptomyces sp. SYP-A7257 may be a potential biological control agent for healthy growth promotion and survival rate improvement of P. notoginseng in the continuous cropping field.

中文翻译：

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对链霉菌属的见解。从三七的根际土壤中分离：聚酮化合物和非核糖体肽的分离，抗菌活性和生物合成潜力。

来自根际土壤的链霉菌是具有多种生物活性的新型次生代谢产物的丰富资源。然而，关于三七人根际链霉菌的聚酮化合物和非核糖体肽的分离，抗菌活性和生物合成潜力的信息仍然很少。因此，本研究的目的是（i）通过16S rRNA基因从三七根际土壤中鉴定出可培养的链霉菌，（ii）评估分离物的抗菌活性，并分析编码聚酮化合物合酶（PKSs）的生物合成基因，以及分离株的非核糖体肽合成酶（NRPS），（iii）检测所选链霉菌的生物活性次生代谢产物，（iv）研究所选分离株对P生长的影响。三七在连作领域。本研究为进一步发现三七根际土壤链霉菌的次生代谢产物及其进一步用于植物生物防治提供了基础。从三七栽培地的12个根际土壤样品中分离出代表42个链霉菌属的42个菌株，并通过16S rRNA基因测序进行了分析。总体而言，在两种培养条件下42种中的40种粗细胞提取物具有抗菌和抗真菌活性。同样，在42个菌株中建立了编码I和II型聚酮化合物合酶（PKS I和PKS II）和非核糖体肽合成酶（NRPS）的生物合成基因。基于高效液相色谱-二极管阵列检测器（HPLC-DAD）筛选特征化学谱，通过高效液相色谱-高分辨率质谱（HPLC-HRMS）评估了菌株SYP-A7257的次级代谢产物谱。最后，使用色谱技术，UV，HR-ESI-MS和NMR技术从菌株SYP-A7257中分离出四种化合物放线菌素X2（F1），真菌染色质（F2），泰国蛋白B（F7）和抗真菌霉素（F8）。还评估了针对测试细菌和真菌的活性。在农场实验中，链霉菌属。SYP-A7257在连作田中显示了三七的健康生长和成活率的提高。我们证明了三七根际根际土壤链霉菌属。聚酮化合物和非核糖体肽的代谢潜力以及生物合成基因PKS I，PKS II和NRPSs的分布和多样性。我们的结果表明，从三七根际土壤中可培养的链霉菌分离株具有产生生物活性次生代谢物的能力。农场实验表明，根际土壤链霉菌属sp。SYP-A7257可能是在连作领域中促进三七的健康生长和提高成活率的潜在生物防治剂。三七具有产生生物活性次生代谢产物的能力。农场实验表明，根际土壤链霉菌属sp。SYP-A7257可能是在连作领域中促进三七的健康生长和提高成活率的潜在生物防治剂。三七具有产生生物活性次生代谢产物的能力。农场实验表明，根际土壤链霉菌属sp。SYP-A7257可能是在连作领域中促进三七的健康生长和提高成活率的潜在生物防治剂。