title: Cuticle-degrading proteases and toxins as virulence markers of Beauveria bassiana (Balsamo) Vuillemin.
abstract: Beauveria bassiana is one of the most known entomopathogenic fungal species and its entomopathogenic mechanism involves several bioactive metabolites, mainly cuticle-degrading enzymes and toxic molecules, which are predicted to play a key role as virulence factors. In this study six Beauveria bassiana strains (B 13/I03, B 13/I11, B 13/I49, B 13/I57, B 13/I63, and B 13/I64) were assayed against Tenebrio molitor larvae. Enzymatic activity of total proteases and specifically Pr 1 and Pr 2, as well as the production of toxic compounds were investigated in each fungal strain. Toxins were detected both in vitro-in medium filtrates and mycelia-and in vivo-in Tenebrio molitor larvae infected by the fungal strains tested. B 13/I11 and B 13/I63 strains showed the most significant entomopathogenic activity against Tenebrio molitor larvae (cumulative mortality rate 100 and 97%, respectively; average survival time 5.85 and 6.74 days, respectively). A widely variable and fungal strain-dependent enzymatic activity of total proteases, Pr 1 and Pr 2 was found. Beauvericin, beauvericin A and bassianolide resulted the most prevalent toxins detected in the substrates analyzed. It has been found that an increase of beauvericin content in vivo resulted significantly correlated to a decrease of Tenebrio molitor larvae average survival time in entomopathogenic bioassay (inverse correlation). The involvement of beauvericin in B. bassiana entomopathogenic process is confirmed; in vitro analysis of cuticle degrading proteases activity and toxins production in relation to the methods adopted resulted insufficient for a rapid screening to determine the virulence of B. bassiana strains against Tenebrio molitor larvae.
authors.affiliation: Research Centre for Agrobiology and Pedology, CREA, Florence, Italy. annarita.cito@isza.it.
authors.forename: Annarita
authors.initials: A
authors.lastname: Cito
authors.affiliation: Research Centre for Agrobiology and Pedology, CREA, Florence, Italy.
authors.forename: Gian Paolo
authors.initials: GP
authors.lastname: Barzanti
authors.affiliation: Research Centre for Agrobiology and Pedology, CREA, Florence, Italy.
authors.forename: Agostino
authors.initials: A
authors.lastname: Strangi
authors.affiliation: Research Centre for Agrobiology and Pedology, CREA, Florence, Italy.
authors.forename: Valeria
authors.initials: V
authors.lastname: Francardi
authors.affiliation: Dipartimento di Biotecnologie, Chimica e Farmacia, Università degli Studi di Siena, Siena, Italy.
authors.forename: Assunta
authors.initials: A
authors.lastname: Zanfini
authors.affiliation: Dipartimento di Biotecnologie, Chimica e Farmacia, Università degli Studi di Siena, Siena, Italy.
authors.forename: Elena
authors.initials: E
authors.lastname: Dreassi
mesh_terms: D000818:Animals; D052982:Beauveria / Q000472:pathogenicity*; D061046:Biological Control Agents; D047630:Depsipeptides / Q000378:metabolism*; D019476:Insect Proteins / Q000378:metabolism*; D007313:Insecta / Q000382:microbiology*; D007814:Larva / Q000382:microbiology; D010447:Peptide Hydrolases / Q000378:metabolism*; D010456:Peptides, Cyclic / Q000378:metabolism*; D010572:Pest Control, Biological; D013712:Tenebrio / Q000382:microbiology*; D037521:Virulence Factors / Q000378:metabolism
chemical_list: D061046:Biological Control Agents; D047630:Depsipeptides; D019476:Insect Proteins; D010456:Peptides, Cyclic; D037521:Virulence Factors; C047663:cuticle proteins, insects; C004456:beauvericin; C035050:bassianolide; D010447:Peptide Hydrolases
keywords: Beauveria bassiana; Beauvericin; Entomopathogenicity; Subtilisin-type Pr 1; Trypsin-like protease Pr 2