Although Pseudomonas chlororaphis O6 (O6) is known to be a rhizobacterium capable of inducing systemic resistance against plant virus, its antiviral products from O6 remain unknown. In the present study, an antiviral cyclic peptide was identified from...
Although Pseudomonas chlororaphis O6 (O6) is known to be a rhizobacterium capable of inducing systemic resistance against plant virus, its antiviral products from O6 remain unknown. In the present study, an antiviral cyclic peptide was identified from the cell-free supernatant of O6. O6 cultures grown on Luria Bertani medium were centrifuged, and the resulting supernatant was extracted with organic solvent, followed by a series of column chromatography and preparative high performance liquid chromatography (HPLC). Bioassay-guided fractionations were involved in the isolation of antiviral products against tobacco mosaic virus (TMV). Time of flight mass spectrometry (TOF-MS) analysis of the isolated product detected $(M+H)^+$ peak at m/z 887.4242 that generated m/z 756.3859, 657.3180, 556.2724, 459.2208, 345.1873, and 171.1130 as the main fragment ions. NMR analyses characterized all protons and carbons of the isolated product. Based on the data, the isolated antiviral product was determined to be a cyclic peptide with molecular formula $C_{39}H_{67}N_9O_{12}S$ consisting of seven different amino acids. The antiviral peptide exhibited more than 95% disease suppression of TMV at 1,000 ${\mu}g/mL$. O6 may play a role in promoting plant growth.