CONICET | Buscador de Institutos y Recursos Humanos

Insect pathogenic fungi are able to produce resistance structures called microsclerotia (MS), which are potential candidates for use in biological control programs. Although oxidative stress was reported to be involved in MS differentiation in some plant pathogenic fungi, there is no information available for entomopathogenic fungi.The main goal of this study was to compare the microsclerotial growth in Beauveria bassiana strain GHA and Metarhizium robertsii strain ARSEF 2575, and to characterize the expression pattern of genes involved in oxidative stress responses and peroxisomal biogenesis. Fungi were cultured in agitated (250 rpm) complete liquid medium with optimal carbon/nitrogen ratio for MS production. Daily aliquots were collected and examined by both optical and transmission electron microscopy (TEM) after staining with the peroxidase activity marker 3,3-diaminobenzidine (DAB). Samples were also used for qPCR analysis to study the expression pattern of superoxide dismutase genes (sod), catalase genes (cat), and peroxins (pex) involved in peroxisome biogenesis. DAB staining showed high peroxidase activity in MS for both strains, with lower staining in hypha close to the borders of the structure. TEM images also showed higher peroxidase activity in mitochondria and peroxisomes. Although pex genes were induced in both strains, Bbpex7 was more induced in B. bassiana, whereas Mrpex19 showed higher expression levels in M. robertsii. At least one of each oxidative stress marker family was also induced in both strains. We conclude that an oxidative stress scenario is triggered in MS producing fungi, including proliferation of peroxisome-like organelles and high peroxidase activity. More studies are need to be carried out to elucidate the relationship between MS formation, oxidative stress and peroxisomal biogenesis to better understand the similarities and differences found in microsclerotial metamorphosis of entomopathogenic fungi.