Abstract
Ralstonia solanacearum is a causative agent of bacterial wilt in many important crops throughout the world. How to control bacterial wilt caused by R. solanacearum is a major problem in agriculture. In this study, we aim to isolate the biocontrol agents that have high efficacy in the control of bacterial wilt. Three new bacterial strains with high antimicrobial activity against R. solanacearum GMI1000 were isolated and identified. Our results demonstrated that these bacteria could remarkably inhibit the disease index of host plant infected by R. solanacearum. It was indicated that strain GZ-34 (CCTCC No. M 2016353) showed an excellent protective effect to tomato under greenhouse conditions. Strain GZ-34 was characterized as Escherichia coli based on morphology, biochemistry, and 16S rRNA analysis. We identified that the main antimicrobial compounds produced by E. coli GZ-34 were cyclo(l-Pro-d-Ile) and cyclo(l-Pro-l-Phe) using electrospray ionization mass spectrometry (ESI-MS) and nuclear magnetic resonance (NMR) analysis. The two active compounds also interfered with the expression levels of some pathogenicity-contributors of R. solanacearum. Furthermore, cyclo(l-Pro-l-Phe) effectively inhibited spore formation of Magnaporthe grisea, which is a vital pathogenesis process of the fungal pathogen, suggesting cyclic dipeptides from E. coli are promising potential antimicrobial agents with broad-spectrum activity to kill pathogens or interfere with their pathogenesis.
Highlights
Bacterial wilt is a systemic, infective, and destructive soil-borne disease caused by Ralstonia solanacearum, commonly known as “plant blast”
Our findings demonstrate that cyclic dipeptides from E. coli might be developed as new potential antimicrobial agents against both bacterial pathogens and fungal pathogens
After analyzing the 16S rDNA sequences of these antagonistic bacterial strains, three bacterial species were identified as new biocontrol agents against R. solanacearum: Pantoea (GZ-33, Center for Culture Collection (CCTCC) No M 2016352)
Summary
Bacterial wilt is a systemic, infective, and destructive soil-borne disease caused by Ralstonia solanacearum, commonly known as “plant blast”. It is an important plant disease in tropical, subtropical, and warm regions [1]. R. solanacearum has an unusually wide host range, infecting more than 200 species belonging to more than 54 botanical families, including economically-important crops [2,3,4]. Molecules 2018, 23, 214 five biovars based on physiological and biochemical characteristics [5,6], and four phylotypes roughly corresponding to geographic origin [7,8] It can survive in soil for many years and can spread through water, rhizosphere contact, and farming [9]. The fast proliferation and propagation of pathogen cells causes plant duct expansion and leads to whole plant wilting and death [11]
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