Water-soluble Cordyceps melanin: a photoprotector that enhances the survival of Beauveria bassiana and Metarhizium acridum conidia under UV-B radiation

TL;DR

This study shows that water-soluble melanin from Cordyceps fungi protects other fungi from UV-B radiation, making them more viable for biological control.

Contribution

The novel use of water-soluble melanin as a photoprotector for entomopathogenic fungi is introduced.

Findings

Hydrophilic melanin increased conidia survival under UV-B by up to 34.9%.

Melanin did not affect virulence or thermotolerance of the fungi.

Cordyceps javanica conidia can serve as a melanin source even after losing viability.

Abstract

Melanin is a pigmentated polymer with antioxidant capacity, and it also plays a role as a quality factor in those fungi that can synthetize it. However, this pigment is soluble only in alkaline solutions, limiting its application. This work used ultrasonication of fungal melanin, extracted from nonviable Cordyceps javanica CHE-CNRCB 307 conidia, and obtained hydrophilic melanin. Suspensions of freshly harvested conidia from Beauveria bassiana CHE-CNRCB 614 or Metarhizium acridum CHE-CNRCB 213 were prepared with a hydrophilic melanin solution at 0.1 mg/mL. These conidia formulations were more resistant to UV-B radiation, up to 34.9%, 26.2%, and 23.3% higher than those without hydrophilic melanin at doses of 10, 14, and 18 kJ/m², respectively, without affecting the virulence or thermotolerance parameters. Based on these results, hydrophilic melanin served as a compatible photoprotector in conidia suspensions from two widely entomopathogenic fungi used in biological control. In addition, the hydrophilic melanin source can be Cordyceps javanica conidia, which keeps melanin beyond the loss of viability, with high added value.

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