Melanin biosynthesis by Frankia strain CeI5

Abstract

Many Frankia strains are pigmented and presumed to produce melanin. However, melanin biosynthesis has yet to be rigorously characterized in Frankia. This study was initiated to determine whether or not Frankia strain CeI5 produced melanin and to identify the biochemical pathway of pigment production. Frankia strain CeI5 first produced a dark pigment in mycelial and other tissue and then in the liquid culture medium when grown in a defined medium containing l-tyrosine. The pigment resisted solvents, lightened when subjected to the action of oxidants, as well as reductants, and produced a flocculent brown precipitate with FeCl(3). Spectroscopic characteristics of the extracted pigment were those of melanin. When subjected to gradual dilution, the absorbance decreased unevenly, occurring in the near red range first, then in the visible range, and lastly in the UV range. This observation might resolve the question of why quite different descriptions of melanin UV-visible light absorption spectra exist in the literature. The tyrosinase cofactor copper greatly enhanced melanin biosynthesis at 5.3 x 10(-6) M, while 1 x 10(-8) M 3,4-dihydroxy-l-phenylalanine hastened pigmentation. The copper-chelating agent KCN and the tyrosinase inhibitor tropolone decreased melanin production at the same concentration of 1 x 10(-5) M. This evidence suggests that Frankia strain CeI5 produces melanin via the Raper and Mason pathway.

Characterization of water-soluble dark-brown pigment from Antarctic bacterium, Lysobacter oligotrophicus

“…1B). These characteristics of absorption were consistent with the UVevisible absorption spectra of the melanins from fungi and bacteria (17,33,34). To confirm the paramagnetic properties and presence of free radicals of melanin, EPR analyses were performed (35).…”

Production and Cytotoxicity of Extracellular Insoluble and Droplets of Soluble Melanin byStreptomyces lusitanusDMZ-3

“…The other chemical reactions of both the pigments were also similar. In all, blackish brown color and total chemical reactions confirm [1, 56] pigments 1 and 2 as insoluble and soluble melanin, respectively.…”

Isolation of Mutants of the Nitrogen-Fixing Actinomycete <i>Frankia</i>

“…5). The brown pigment could be melanin because a Frankia strain is reported to produce the compound (23). As shiro1 and shiro2 shared two identical mutations in Francci3_2727 and Francci3_2745 (Table S2), these mutations are potentially responsible for the aberrant phenotype.…”