Identification of Beauveria bassiana extracellular protease as a virulence factor in pathogenicity toward the migratory grasshopper, Melanoplus sanguinipes

Beauveria bassiana extracellular protease was shown to hydrolyze protein in cuticle of the migratory grasshopper, Melanoplus sanguinipes. Protease-proficient and protease-deficient strains of B. bassiana were assessed for production of extracellular protease in liquid culture and their virulence, as measured by LT50, toward M. sanguinipes. A uv irradiation-derived protease-deficient mutant strain produced less than 10% of protease when compared to the protease-proficient strains when grown in 1% (w/v) gelatin liquid medium or 1% (w/v) ground M. sanguinipes cuticle liquid medium. The protease-proficient strains showed the lowest LT50 (5.71–6.80 days) against the migratory grasshopper, while the protease-deficient strain had the highest LT50 (11.34 days). There was a negative relationship between protease production after 2 days of growth in liquid culture by the various strains and their associated LT50. We conclude that, in this study, protease production by the B. bassiana protease-deficient strain was low enough so that it extended the time course of pathogenesis toward M. sanguinipes.