Optimization of Melanin Production by Streptomyces antibioticus NRRL B-1701 Using Arthrospira (Spirulina) platensis Residues Hydrolysates as Low-Cost L-tyrosine Supplement

Abstract

Melanin is a functional pigment that is used in various products. It can be produced by Streptomyces antibioticus NRRL B-1701 when supplemented with L-tyrosine. Arthrospira (Spirulina) platensis is a cyanobacterium with high protein content, including the protein phycocyanin (PC). During PC’s extraction, biomass residues are generated, and these residues still contain various amino acids, especially L-tyrosine, which can be used as a low-cost supplement for melanin production. Thus, this study employed a hydrolysate of A. platensis biomass residue for L-tyrosine substitution. The effects of two drying methods, namely, lyophilization and dying via a hot air oven, on the proximate composition and content of L-tyrosine in the biomass residue were evaluated. The highest L-tyrosine (0.268 g L-tyrosine/100 g dried biomass) concentration was obtained from a hot-air-oven-dried biomass residue hydrolysate (HAO-DBRH). The HAO-DBRH was then used as a low-cost L-tyrosine supplement for maximizing melanin production, which was optimized by the response surface methodology (RSM) through central composite design (CCD). Using the RSM–CCD, the maximum level of melanin production achieved was 0.24 g/L, which is approximately four times higher than it was before optimization. This result suggests that A. platensis residue hydrolysate could be an economically feasible and low-cost alternative source of L-tyrosine for the production of melanin.

Streptomycetes as Microbial Cell Factories for the Biotechnological Production of Melanin

“…In general, purified melanin pigment is ground with KBr powder in an agate mortar (in a ratio of 1 or 2 mg of melanin to 200 mg of KBr), mixed, and set up in the form of a disc that is then scanned between 4000 and 400 cm −1 . The different origins of melanin, its solubility, and the procedures employed to purify it, slightly change the FT-IR signals [ 39 ] ( Table 4 ). A summary of the main FT-IR signals of the different types of melanin produced by the diverse Streptomyces strains, as found in the literature, is reported in Table 4 .…”

“…The MelC1 protein determines the effective secretion of tyrosinase in the medium, but mutants, defective in the melC1 gene and thus in the secretion of the enzyme, have also been found [ 27 ]. In the literature, several new Streptomyces strains that can produce melanin were isolated from soil samples [ 22 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 ] from different locations in Egypt, India, and Turkey, or from forest or lake environments, also eventually associated with rhizosphere or plants [ 32 , 36 , 37 , 38 , 39 ] ( Figure 3 ). Some others, instead, have been isolated from marine sediments [ 40 , 41 , 42 , 43 , 44 , 45 ] in India and China, for example, or eventually associated with marine animals like the sea cucumber Stichopus vastus [ 46 ] ( Figure 3 ).…”

“…The concentration of various medium components, including yeast extract, soluble starch, CuSO 4 , and the A. platensis hydrolysate itself, was optimized through a CCD model. The results indicated a significant effect of yeast extract and the hydrolysate supplementation on melanin production, up to a maximum of 0.24 g/L [ 39 ] ( Table 1 ). Streptomyces antibioticus NRRL B-1701 also showed an ability to use non-natural amino acids, such as N-acetyl-L-tyrosine and L-tyrosine ethyl ester, as substrates for tyrosinase activity [ 39 ].…”

“…The results indicated a significant effect of yeast extract and the hydrolysate supplementation on melanin production, up to a maximum of 0.24 g/L [ 39 ] ( Table 1 ). Streptomyces antibioticus NRRL B-1701 also showed an ability to use non-natural amino acids, such as N-acetyl-L-tyrosine and L-tyrosine ethyl ester, as substrates for tyrosinase activity [ 39 ]. Higher melanin concentrations were reached only with recombinant strains like S. kathirae , which had multiple copies of the melC gene, and it was able to produce up to 28.8 g/L of the pigment (Guo et al, 2015).…”

“…Tyrosinase genes from Streptomyces lusitanus and Streptomyces kathirae were also successfully expressed in Escherichia coli, and the recombinant strains were able to produce eumelanin when grown on L-tyrosine-supplemented medium [38]. In another example, instead, the tyrosinase genes from Streptomyces antibioticus were inserted in another recombinant E. coli JM109 strain and put under the transcriptional control of a phage T5 promoter and of two lac operators [39]. Melanin pigments with a diverse range of colors from greenish-brown to brownish-black were produced at the same time by an isolated marine actinomycete [41].…”