A putative α-glucoside transporter gene BbAGT1 contributes to carbohydrate utilization, growth, conidiation and virulence of filamentous entomopathogenic fungus Beauveria bassiana

Carbohydrate transporters are critical players mediating nutrient uptake during saprophytic and pathogenic growth for most filamentous fungi. For entomopathogenic fungi, such as Beauveria bassiana, assimilation of α-glucosides, in particular, trehalose, the major carbohydrate constituent of the insect haemolymph, has been hypothesized to represent an important ability for infectious growth within the insect hemocoel. In this study, a B. bassiana α-glucoside transporter homolog was identified and genetically characterized via generation of a targeted gene disruption mutant. Trehalose utilization was compromised in the mutant strain. In addition, inactivation of the α-glucoside transporter resulted in decreased conidial germination, growth, and yield on various carbohydrates (α-glucosides, monosaccharides and polyols) as compared to the wild-type strain. Insect bioassays revealed decreased mean lethal mortality time using both topical and intrahemocoel injection assays, although final mortality levels were comparable in both the mutant and wild type. Gene expression profiles showed altered expression of other putative transporters in the knockout mutant as compared to the wild type. These results highlighted complex sugar utilization and responsiveness in B. bassiana and the potential role for trehalose assimilation during fungal pathogenesis of insects.