Impact of insect midgut-like environment on conidia of entomopathogenic fungus Beauveria bassiana.

The conidia of a transgenic strain(Bb2860G6) that steadily expresses green fluorescence protein were suspended in the solutions of 0.5% enzymes similar to those present in different insect midguts and then incubated at 25 ℃ or 35 ℃ for 4 h,followed by examining the fluorescence intensity of conidia(i.e.,cell permeability) through flow cytometry and the structural changes of conidial wall under scanning electron microscope.The structural changes of conidial wall treated by different enzymes were associated with variation of the conidial fluorescence intensity.As a result,the fluorescence intensity of the treated conidia was significantly enhanced by treatments with proteinase K,pronase E,cellulase,trypsin and α-amylase respectively,but reduced by laminarinase,glucosidase and snailase.A mixture of 0.5% proteinase K with 0.5% cellulase or 0.5% trypsin with 0.5% cellulase decreased the fluorescence intensity more than a single enzyme,and the decreases varied significantly at pH 5-11,which occur in the midgut environments of different insects.Conspicuous changes of the conidial wall were also observed after 4 h treatment with the digestive enzymes.The results imply that insect midgut environment may affect the wall structure and activity of B.bassiana conidia.