Identification of Cyclic Dipeptides from Escherichia coli as New Antimicrobial Agents against Ralstonia Solanacearum

is a causative agent of bacterial wilt in many important crops throughout the world. How to control bacterial wilt caused by 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 GMI1000 were isolated and identified. Our results demonstrated that these bacteria could remarkably inhibit the disease index of host plant infected by . 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 based on morphology, biochemistry, and 16S rRNA analysis. We identified that the main antimicrobial compounds produced by 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 . Furthermore, cyclo(l-Pro-l-Phe) effectively inhibited spore formation of , which is a vital pathogenesis process of the fungal pathogen, suggesting cyclic dipeptides from are promising potential antimicrobial agents with broad-spectrum activity to kill pathogens or interfere with their pathogenesis.