Abstract
Ralstonia solanacearum is an important soil-borne bacterial plant pathogen. In this study, an actinomycete strain named NEAU-HV9 that showed strong antibacterial activity against Ralstonia solanacearum was isolated from soil using an in vitro screening technique. Based on physiological and morphological characteristics and 98.90% of 16S rRNA gene sequence similarity with Streptomyces panaciradicis 1MR-8T, the strain was identified as a member of the genus Streptomyces. Tomato seedling and pot culture experiments showed that after pre-inoculation with the strain NEAU-HV9, the disease occurrence of tomato seedlings was effectively prevented for R. solanacearum. Then, a bioactivity-guided approach was employed to isolate and determine the chemical identity of bioactive constituents with antibacterial activity from strain NEAU-HV9. The structure of the antibacterial metabolite was determined as actinomycin D on the basis of extensive spectroscopic analysis. To our knowledge, this is the first report that actinomycin D has strong antibacterial activity against R. solanacearum with a MIC (minimum inhibitory concentration) of 0.6 mg L−1 (0.48 μmol L−1). The in vivo antibacterial activity experiment showed that actinomycin D possessed significant preventive efficacy against R. solanacearum in tomato seedlings. Thus, strain NEAU-HV9 could be used as BCA (biological control agent) against R. solanacearum, and actinomycin D might be a promising candidate for a new antibacterial agent against R. solanacearum.
Highlights
Tomato is one of the world’s most important vegetable crops, with a global annual yield of approximately 160 million tons [1,2]
Bacterial wilt caused by R. solanacearum is a serious and common disease, which reduces the yield of tomato and many other crops in tropical, subtropical, and warm-temperature regions of the world [6]
By using 16S rRNA gene sequence analysis, combined with morphological, cultural and physiological characteristics, the results showed that strain NEAU-HV9 belongs to members of the genus Streptomyces and was most closely related to Streptomyces panaciradicis 1MR-8T and Streptomyces sasae JR-39T with gene sequence similarities of 98.90% and 98.89%, respectively
Summary
Tomato is one of the world’s most important vegetable crops, with a global annual yield of approximately 160 million tons [1,2]. In China, long term continuous cropping is the main planting practice for tomato, which has led to serious soilborne diseases [3]. Ralstonia solanacearum [4] is an important soilborne bacterial plant pathogen [5]. Bacterial wilt caused by R. solanacearum is a serious and common disease, which reduces the yield of tomato and many other crops in tropical, subtropical, and warm-temperature regions of the world [6]. Because of worldwide distribution and a large host range of more than 200 plant species in 50 families, including pepper, tomato, tobacco, potato, peanut, and banana, this soil bacterium has been recognized as one of the causative agents of bacterial wilt disease and is one of the leading models in pathogenicity [5]. New natural resources and antibiotics for suppressing this soilborne disease are needed
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