Pathogenicity and characterization of a novel Bacillus cereus sensu lato isolate toxic to the Mediterranean fruit fly Ceratitis capitata Wied.

• A new Bacillus cereus s.l. isolate is toxic to Ceratitis capitata larvae.
• Spores of B. cereus s.l. (109/g of diet) cause sub-lethal effects on the Medfly.
• The insecticidal action is partly associated to an extra-spore fraction.
• The extra-spore proteome contains putative virulence factors.

The lethal and sub-lethal effects of sporulated cultures of a novel Bacillus cereus sensu lato strain lacking detectable cry genes and identified through morphological and genetic analyses, have been studied on the Mediterranean fruit fly Ceratitis capitata. The lethal effects on young larvae were concentration dependent, with a median lethal concentration (LC50) of 4.48 × 108 spores/g of diet. Sporulated cultures of this strain significantly extended development time and reduced immature survival, and the size of emerging fly adults. Besides spores, the toxicity has been associated to the insoluble extra-spore fraction characterized through a proteomic approach. The profile of the extra-spore protein fraction (ES) showed major protein bands within the 35–65 kDa range. The results of mass spectrometry analysis highlighted the presence of putative virulence factors, including members of protein families previously associated to the insecticidal action of other microbial entomopathogens. These proteins include metalloproteases, peptidases and other enzymes.

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