Pyochelin isolated from Burkholderia arboris KRICT1 carried by pine wood nematodes exhibits phytotoxicity in pine callus

Abstract

Abstract Pine wilt disease is a very complex disease known to be caused by the pine wood nematode, Bursaphelenchus xylophilus, and its accompanying bacteria. The phytotoxin-producing bacteria have been reported to be involved in the development of pine wilt disease. In this study, we attempted to characterise phytotoxins produced by Burkholderia arboris KRICT1, which was carried by the pine wood nematode. It produced phytotoxic compounds in the pine seedling assay, and the ethyl acetate (EtOAc) layer of the fermentation broth of the strain displayed phytotoxic activity on the pine callus of Pinus densiflora. One active compound was isolated from the EtOAc layer by repeated Sephadex LH-20 column chromatography and preparative TLC. Using mainly mass spectroscopy and nuclear magnetic resonance (NMR) spectroscopy, the chemical structure was determined to be that of pyochelin (a mixture of two interconvertible diastereoisomers, pyochelin I and II). Pyochelin exposure reduced the viability of pine callus. Compared with phenylacetic acid, a phytotoxin produced by Bacillus spp. that was transmitted by B. xylophilus in Japan, pyochelin showed much stronger phytotoxicity. The results suggested that pyochelin might play a role in the wilting process of pine wilt disease.