An extracellular protease from Brevibacillus laterosporus G4 without parasporal crystals can serve as a pathogenic factor in infection of nematodes.

Brevibacillus laterosporus is an aerobic spore-forming bacterium with the ability to produce canoe-shaped lamellar parasporal inclusions adjacent to spores. An isolate named G4 was identified as a B. laterosporus which does not produce parasporal crystals and shows significant toxic activity toward nematodes. Crude extracellular protein extract from culture supernatant of B. laterosporus G4 killed the nematodes within 12 h and finally destroyed the targets within 24 h, which suggested possible proteinaceous pathogeny. A homogeneous extracellular protease with nematicidal activities, purified by chromatography, confirmed the hypothesis that it might serve as a pathogenic factor during infection of the G4 strain. Characterization of the purified protease revealed a molecular mass of 30 kDa and optimum activity at pH 10 and 50 degrees C. The protease hydrolyzed relatively broad substrates including collagen and the cuticle of nematodes, and histopathological observations demonstrated the resulting destroyed nematode cuticle upon treatment by purified protease. Our present study reveals that extracellular protease, but not previously reported parasporal crystals, can be employed in infection against invertebrates by the B. laterosporus G4 strain.