Dark Pigments in Entomopathogenic Fungal Microsclerotia: Preliminary Evidence of a 1,8-Dihydroxynaphthalene-melanin-like Compound in Metarhizium robertsii

ESPÍN-SÁNCHEZ, DAYSI; LAUTARO PREISEGGER; ROMINA MAZZOLENIS; MARIANELA SANTANA; MARIO CARLOS NAZARENO SAPARRAT; PEDRINI, NICOLÁS; HUARTE-BONNET, CARLA

Journal of Fungi

Multidisciplinary Digital Publishing Institute (MDPI)

Lugar: Basel; Año: 2023 vol. 9

Metarhizium robertsii microsclerotia are fungal aggregates composed of compacted, pig-mented hyphae. As they are highly tolerant to desiccation and produce infective conidia, they arepromising candidates to be formulated as bioinsecticides. Despite this potential, the nature of thepigments within these structures remains unclear. In this study, routine culture media used for thedifferentiation of M. robertsii microsclerotia were supplemented with four melanin inhibitors, andthe resulting propagules were characterized. Inhibitors of the 1,8-dihydroxynaphthalene (DHN)-melanin biosynthetic pathway such as tricyclazole and guaiacol induced significant phenotypic andmolecular modifications in the obtained M. robertsii propagules, which exhibited a more sphericalshape, reduced size, and increased susceptibility to desiccation, heat, and oxidative stress thanmicrosclerotia obtained without inhibitors. Additionally, genes encoding for a polyketide synthase(Mrpks2) and a putative 1,3,6,8-tetrahydroxynaphthalene reductase (Mrthnr), potentially involved inthe DHN-melanin biosynthetic pathway, were upregulated in fungi grown in the inhibitor-addedmedia. In conclusion, M. robertsii microsclerotia contain melanins of type DHN that might play a rolein both microsclerotia differentiation and environmental stress tolerance.