Synthesis and role of melanin for tolerating in vitro rumen digestion in Duddingtonia flagrans, a nematode-trapping fungus

Deivid França Freitas,Olney Vieira-Da-Motta,Luciana Da Silva Mathias,Roberto Weider De Assis Franco,Raphael Dos Santos Gomes,Ricardo Augusto Mendonça Vieira,Letícia Oliveira Da Rocha,Fabio Lopes Olivares,Clóvis De Paula Santos

doi:10.1080/21501203.2019.1631896

Deivid França Freitas, Olney Vieira-Da-Motta + Show 7 more

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https://doi.org/10.1080/21501203.2019.1631896

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Journal: Mycology	Publication Date: Jun 20, 2019
Citations: 7	License type: open-access

Affiliation: State University of Norte Fluminense

Abstract

ABSTRACTWe describe the synthesis and a function of melanin in Duddingtonia flagrans, a nematode-trapping fungus. We tested various culture media treated with L-DOPA, glucose and tricyclazole on fungal growth and melanin distribution using infrared spectroscopy (IS), electron paramagnetic resonance (EPR) and transmission electron microscopy (TEM). In vitro rumen digestion was used to test the environmental stress and then to evaluate the capacity of this fungus to trap nematode larvae. The growth and melanization of the fungus after 21 days of incubation at 30°C were best in Sabouraud dextrose medium. IS indicated the presence of melanin in D. flagrans, with similar bands for commercial melanin used as a control, and assigned the values obtained by EPR (g of 2.0051 ± 0.0001) to the production of melanin by the fungus. TEM indicated that melanin was produced in melanosomes but was not totally inhibited by tricyclazole. Within the limits of experimental error, the predatory activity of fungus treated with tricyclazole was drastically affected after 27 h of in vitro anaerobic stress with rumen inoculum. The deposition of melanin particles on the fungal cell wall contributed to the maintenance of D. flagrans predatory abilities after in vitro anaerobic ruminal stress.

Highlights

Melanins are amorphous substances formed by the polymerization of phenolic and indolic compounds and are found in all biological systems, indicating an early evolutionary origin (Butler et al 2009; Solano 2014)
We analyzed the influence of culture medium on pigmentation in D. flagrans supplemented with 1 mM L-DOPA, using glucose as a carbon source at concentrations of 2–20% (w/v)
D. flagrans pigmentation was higher at glucose concentrations similar to the commercially available Sabouraud culture media, which was added to the medium at 2% and intensified to maximal staining at concentrations of 2–8%

Summary

Introduction

Melanins are amorphous substances formed by the polymerization of phenolic and indolic compounds and are found in all biological systems, indicating an early evolutionary origin (Butler et al 2009; Solano 2014). Melanin in the cell walls of fungi can increase survival by protecting against ultraviolet radiation (Allam and El-Zaher 2014), traumatic damage (Eisenman and Casadevall 2012) and extreme temperatures and pressures in, for example, polar regions or deserts (Rosa et al 2010). Melanin pigments are very common in the Fungi kingdom (Solano 2014), melanogenesis is restricted to certain stages of mycelial development and sporulation or to defensive reactions against damage by environmental stressors. They are abundant and can be associated with cell walls or subcellular organelles (Franzen et al 2008). Melaninproducing organisms can usually synthesize it by two main pathways, either from an endogenous substrate involving 1,8-dihydroxynaphthalene (DHN) and the action of polyketide synthase, or alternatively by an exogenous pathway with the addition of L-3,4-dihydroxyphenylalanine (L-DOPA)

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