Isolation of the Novel Strain F9 and Identification of Lipopeptide Extract Components Responsible for Activity against subsp. .

Citrus canker, caused by subsp. (), is a quarantine disease that seriously affects citrus production worldwide. The use of microorganisms and their products for biological control has been proven to be effective in controlling disease. In this study, a novel antagonistic strain was isolated and identified as F9 by morphological and molecular analysis. The lipopeptide extract of F9 (F9LE) effectively inhibited the growth of in an agar diffusion assay and restrained the occurrence of canker lesions in a pathogenicity test under greenhouse conditions. Consistent with these findings, F9LE treatment significantly inhibited the production of extracellular enzymes in cells and induced cell wall damage, with leakage of bacterial contents revealed by scanning electron microscopy and transmission electron microscopy analyses. In addition, F9LE also showed strong antagonistic activity against a wide spectrum of plant pathogenic bacteria and fungi. Furthermore, using electrospray ionization mass spectrometry analysis, the main antimicrobial compounds of strain F9 were identified as three kinds of lipopeptides, including homologues of surfactin, fengycin, and iturin. Taken together, our results show that F9 and its lipopeptide components have the potential to be used as biocontrol agents against , and other plant pathogenic bacteria and fungi.