Characterization of melanin produced by a wild-type strain of Bacillus thuringiensis

Abstract

Bt L-7601 is a UV resistant wild-type strain, which belongs to Bacillus thuringiensis subsp. dendrolimus serotype H4a4b. It was isolated from nature, and produced a dark brown pigment during the exponential phase of growth. Bt L-7601 had the ability to produce pigment in a general nutrition-abundant medium, which had no L-tyrosine. The pigment was identified as melanin based on chemical testing, its light absorbance, and FT-IR analysis. Bt L-7601 has a strong resistance to UV light. After 30 min irradiation its survival rate was 17 times higher than that of the strain B. thuringiensis subsp. colmeri 15A3, which had no pigment. Results of the bioassays of residual insecticidal activity of Bt formulation with and without pigment produced by Bt L-7601 against larvae of Helicoverpa armigera and Spodoptera exigua after exposure to UV irradiation showed that the pigment is an excellent UV protective agent for the insecticidal proteins.

Biocatalytic formation of synthetic melanin: The role of vanadium haloperoxidases, L-DOPA and iodide

“…However, a broad band at 3000 cm − 1 may be assigned to the -OH stretching, the bands in the region 1600-1650 cm − 1 may be due to aromatic C C and COO stretches and the the phenolic COH and indolic NH bends are visible at 1380-1400 cm − 1 . These spectra are also in good agreement to melanin spectra obtained by other authors [25,27,28].…”

“…In order to compare UV-vis absorption spectra of the black lyophilized product and commercially available melanin, solutions were prepared as described in the experimental section [27]. After cooling to room temperature, the solutions were spectrophotometrically scanned from 200 to 600 nm.…”

Melanins: Skin Pigments and Much More—Types, Structural Models, Biological Functions, and Formation Routes

“…Similarly to Streptomyces, other species such as Marinomonas mediterranea [131,132] and Bacillus thuringiensis [133,134] contain active tyrosinases and they become heavily pigmented in the presence of L-tyrosine. All these bacterial melanins contain nitrogen, and their structure is similar to animal eumelanin.…”

Secondary metabolites of soil Bacillus spp.

“…It was shown that melanin is an excellent photoprotective agent and because of this photoprotection of the mosquitocidal activity of B. thuringiensis israelensis, using melanin, has been studied. Several research groups have obtained B. thuringiensis mutants producing melanin from B. thuringiensis (Espinasse et al 2002;Saxena et al 2002) but there are wildtype strains of B. thuringiensis that produces melanin as a secondary metabolite (Che et al 2004). Despite the appearance of melanin together with b-exotoxin I during growth, regulation of the production of pigment is probably independent of that of b-exotoxin I.…”