**5. Conclusions**

In summary, this study found that *Streptomyces* sp. NEAU-HV9 exerted significant antibacterial activity against *R. solanacearum*, and actinomycin D, which was produced by *Streptomyces* sp. NEAU-HV9, exhibited a minimum inhibitory concentration (MIC) against *R. solanacearum* of 0.6 mg L−<sup>1</sup> (0.48 μmol L−1). In addition, *Streptomyces* sp. NEAU-HV9 and actinomycin D can effectively inhibit the occurrence of *R. solanacearum*. From the results, it is obvious that *Streptomyces* sp. NEAU-HV9 is an important microbial resource as a biological control against *R. solanacearum* and actinomycin D is a promising candidate for the development of potential antibacterial biocontrol agents.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2076-2607/8/3/351/s1: Table S1: Growth and cultural characteristics of strain NEAU-HV9 after 2 weeks at 28 ◦C; Table S2: Physiological and biochemical characteristics of strain NEAU-HV9; Figure S1: Cultural characteristics of strain NEAU-HV9 observed on ISP 1, ISP 2, ISP 3, ISP 4, ISP 5, ISP6, ISP7, Nutrient agar, Bennett's agar and Czapek's agar after being incubated at 28 ◦C for 2 weeks; Figure S2: Bioactivities of the supernatant and cell pellet of NEAU-HV9 against *R. solanacearum*; Figure S3: The HPLC profiles of crude extract produced by *Streptomyces* NEAU-HV9; Figure S4: Mass Spectrometry of actinomycin D (C62H86N12O16Na: 1277.6); Figure S5: 1H NMR of actinomycin D; Figure S6: 13C NMR of actinomycin D; Figure S7: The HPLC profiles of commercial actinomycin D; Figure S8: Bioactivities of commercial actinomycin D and the main product of NEAU-HV9 against *R. solanacearum*; Figure S9: Control efficiency of strain NEAU-HV9 against *R. solanacearum*; Figure S10: Control efficiency of the actinomycin D and strain NEAU-HV9 against *R. solanacearum*.

**Author Contributions:** L.L., X.H., X.L., H.W. and Y.W. performed the experiments. X.Z., L.Z. and P.C. analyzed the data. L.L. wrote the paper. X.W. and X.H. prepared the figures and tables. J.Z. and W.X. designed the experiments and reviewed the manuscript. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was supported in part by grants from the National Natural Youth Science Foundation of China (No. 31701858), the China Postdoctoral Science Foundation (2018M631907), the Heilongjiang Postdoctoral Fund (LBH-Z17015), the University Nursing Program for Young Scholars with Creative Talents in Heilongjiang Province (UNPYSCT-2017017) and the "Young Talents" Project of Northeast Agricultural University (17QC14).

**Conflicts of Interest:** The authors declare that there are no conflicts of interest.
