Beauveria bassiana produces microsclerotia-like propagules with active peroxisome biogenesis

E.K.K. FERNANDES; C. HUARTE-BONNET; N. PEDRINI; F.R.S. DA PAIXAO

Simposio; International symposium of fungal stress 2017; 2017

Entomopathogenic fungi are able to produce several types of propagules such as aerial conidia in solid media, or blastospores, submerged conidia and microsclerotia in liquid cultures. Microsclerotia (MS) are usually melanized compact hyphal aggregates that are tolerant to dessication. As far as we known, there are no reports about the production of melanized microsclerotia by Beauveria bassiana isolates. The aim of this study was to describe microsclerotial growth in B. bassiana and to start with studies about the molecular and physiological mechanisms implicated in the production of these propagules. B. bassiana strain GHA was cultured in complete liquid medium for 4 days at 26ºC with vigorous agitation (250 rpm). Microsclerotia-like structures were separated by centrifugation and processed for microscopy observation and real time qPCR analysis. Under this culture conditions, B. bassiana was able to produce compact brownish aggregates that were able to germinate and produce viable conidia after desiccation. Optical microscope images showed similarity in form, structure and size with microsclerotia reported from other entomopathogens, and staining with 3,3-diaminobenzidine (DAB) revealed high peroxidase activity. Genes encoding for peroxisome biogenesis factors, named peroxins, showed high expression levels (up to 17-fold induction), i.e., Bbpex5, Bbpex7, Bbpex14/17 and Bbpex19 genes in 4 days cultures compared with conidia used as starting inocula. Additional studies are being carried out to elucidate the relationship between microsclerotia formation and peroxisomal biogenesis, as same as stress tolerance, cell surface alterations and virulence against insect hosts.