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Keywords:

  • melanin;
  • tyrosinase;
  • isolation;
  • Streptomyces kathirae ;
  • medium optimization

Abstract

Forty-five bacterial strains that produced diffusive pigments were isolated from 40 soil samples. Maximum pigment production was from a Streptomyces kathirae strain designated SC-1. The diffused pigment was characterized by UV–visual and infrared spectroscopy, MS and 1H nuclear magnetic resonance imaging, and was confirmed as melanin. This may be the first report of melanin production by S. kathirae. To enhance melanin production, the culture medium was optimized by conducting a series of batch fermentations in a defined medium, and the results were analysed statistically using a response surface method. The optimal culture medium comprised 3.3 g L−1 amylodextrine, 37 g L−1 yeast extract, 5 g L−1 NaCl, 0.1 g L−1 CaCl2 and 54.4 μM CuSO4. The pH of this medium was 6.0. Under optimal conditions, the melanin concentration was maximized at 13.7 g L−1, c. 8.6-fold higher than obtained in suboptimal medium. To our knowledge, the results provide novel data on melanin fermentation, and identify an excellent candidate for industrial-scale microbial fermentation of melanin.