Isolation and identification of chemical constituents from the bacterium Bacillus sp. and their nematicidal activities.

A strain SMrs28 was isolated from the rhizosphere soil of a toxic plant Stellera chamaejasme and identified as Bacillus sp. on the basis of morphological and partial 16S rRNA gene sequence analysis. The crude extract of SMrs28 fermentation broth showed strong nematocidal activities in preliminary test. To define the active nematocidal metabolites of SMrs28, a novel compound (1), 4-oxabicyclo[3.2.2]nona-1(7), 5,8-triene, along with five known compounds (2-6), were isolated from the strain by various column chromatographic techniques and characterized on the basis of spectroscopic analysis. Results of the in vitro nematicidal tests showed that the metabolites presented different levels of activity at certain exposure conditions. Compounds (1-3) displayed LC50 values of 904.12, 451.26, 232.98 µg/ml and 1594.0, 366.62, 206.38 µg/ml against Bursaphelenchus xylophilus and Ditylenchus destructor at 72 h, respectively. This is the first report of the nematicidal activity of the compounds as constituents of Bacillus sp.. Our findings help to find potential chemical structures to develop nematicides from microbial source for the management of nematode-infected plant diseases.