Chitosan increases conidiation in fungal pathogens of invertebrates

Antifungal activity of chitosan on plant pathogenic fungi has been widely studied, but little is known about the effect of chitosan on fungal biocontrol agents. In this work, we characterize the increase of conidiation induced by chitosan in fungal pathogens of invertebrates (FPI). Chitosan increased conidiation of FPI, including Beauveria bassiana, widely used as mycoinsecticide, and did not affect conidia viability or pathogenicity. Increased conidiation induced by chitosan is shown to be concentration dependent and is not associated to growth inhibition as observed for the mycoparasitic fungus Trichoderma harzianum. Real-time reverse transcription polymerase chain reaction was used to study transcript levels of two genes involved in conidiation in B. bassiana, the regulatory G protein signaling gene Bbrgs1 and the hydrophobin gene hyd1, at different chitosan concentrations. Higher levels of Bbrgs1 and hyd1 transcripts were detected on chitosan-amended media. No correlation with chitosan concentration was observed for expression of Bbrgs1 unlike hyd1. Bbrgs1 deletion mutant Bbrgs1 showed that chitosan-induced conidiation is independent of Bbrgs1, suggesting an alternative mechanism controlling conidiation in B. bassiana. Our data supports that sporulation increases by chitosan, with spores retaining their viability and pathogenicity, which makes chitosan a suitable compound to increase conidia production in fungi with applications in fungal biotechnology.