Characterization of Nematicidal Activity and Nematode-Toxic Metabolites of a Soilborne Isolate.

The increasing prevalence of crop-threatening root-knot nematodes (RKNs) has stimulated extensive research to discover effective nematicides. A highly focused strategy for accomplishing this is the development of biocontrol agents by a variety of soilborne microorganisms, as different bacterial metabolites have demonstrated promising nematicidal activities. In this study, we characterized the nematicidal and suppressive activity of a bacterial isolate against the agriculturally important RKN and the model nematode , and the main -toxic metabolite of the strain. After a preliminary screening of 22 bacterial isolates with a corrected mortality (CM) of whole-cell culture greater than 50% against from different RKN-incident soils in China, a total of 14 isolates with CM of the supernatant of culture suspension (SCS) higher than 50% against both and were rescreened. An isolate with the highest CM of 86.1% and 95.0% for and , respectively, was further identified as the species via morphological examination, physiological and biochemical assays and alignment analysis of 16S rRNA gene sequences. The SCS of this strain, namely, MB756, exhibited synchronous killing activity along with significant detrimental effects on the growth, brood size, and locomotion of . The effects of heat treatment, pH, inoculations, and protease K proteolysis on the CM of MB756 SCS were evaluated. A major -toxic substance in the MB756 SCS was assayed and identified using thin-layer chromatography, column chromatography and high-performance liquid chromatography with a mass spectrometer, and it was preliminarily identified as 2-ethylhexan-1-ol, with a molecular formula of CHO and a molecular weight of 130.3 Da.