Optimizing production of a biopesticide protectant by black yeast

Abstract

Natural protection of the Bacillus thuringiensis-based biopesticides from inactivation by the UV component of the cosmic rays constitutes a big challenge to environmentalists, health concerned groups, and industry. Melanin pigment produced by a variety of microbes has the capabilities of protecting these types of biopesticides. A black melanin produced by a locally isolated strain of the yeast Hortaea werneckii EGYNDA08 possesses the qualities of a sun protectant agent. This UV bio-protectant increased the killing potency of a locally isolated B. thuringiensis subsp. aegypti (Bt-C18)-based biopesticide ninefold upon feeding the first instar larvae of the cotton leaf worm, Spodoptera littrolis. This black melanin was extracted, characterized, and exposed to different optimization process for the purpose of enhancing its productivity. The optimization process employed medium engineering techniques to generate a suitable cheap production medium not only at bench-scale level but also at the bioreactor level. These optimization techniques have led to increase the melanin produced by the local isolate of Hortaea werneckii EGYNDA08 up to 228 mg/l compared to 8 mg/l prior to optimization. This study concluded that black yeast melanin could be used at a wide range as a potential green alternative for the conventional chemically based sunscreens that currently used to protect biopesticides from inactivation by the cosmic rays.