Abstract
PurposeTo characterize and optimize the productivity of melanin using an extremotolerant actinobacterium, Dietzia schimae NM3, for the first time.MethodsAn extracellular brown pigment produced by D. schimae NM3 in the nutrient broth and cheese whey medium by adding L-tyrosine. The extracted melanin was analyzed by UV-visible, HPLC, and FTIR assays. The radical scavenging activity (by DPPH) and sun protection factor (SPF) of the extracted melanin were measured. The melanin cytotoxicity was assayed by MTT and chromate biosorption was measured by atomic absorption spectroscopy. Finally, melanin production by D. schimae NM3 was optimized by response surface methodology (RSM) using Box-Behnken design in the whey medium.ResultThe purified melanin showed similar peak to the standard melanin (SIGMA) at 3.5 min in HPLC, and C=O bands, NH2, CH, C-N, and aromatic groups by FTIR. The radical scavenging activity (by DPPH) and SPF of the extracted melanin were obtained 188.9% and 20.22, respectively. Using MTT assay, the melanin revealed non-toxic effect on the normal human fibroblast (HFB) cell culture. The melanin yield 790 mg l−1, and tyrosinase activity 3400 U ml−1 were obtained in the medium contained whey powder [5% (w v−1)], L-tyrosine 2.5 g l−1, CuSO4 0.013 g l−1, and pH 10.5, incubated at 32 °C for 3 days. The ANOVA results indicated significant P-value, model F-value, and probability, with insignificant lack of fit. After optimization with mono-factors, the nutrient broth came up with melanin yield as 1.2 g l−1 and tyrosinase activity as 4040 U ml−1.ConclusionThis is the first report of melanin production by D. schimae NM3 and this natural melanin showed valuable biological properties such as high antioxidant activity and radioprotection (SPF) and the biocompatibility to human cell line.
Highlights
Dietzia genus is an actinobacterium consuming many compounds, tyrosine is the sole carbon source for producing melanin pigment (Koerner et al 2009)
Melanin production and purification The nutrient broth containing 2 g l−1 L-tyrosine was inoculated by 5% (v v−1) of the D. schimae culture (108 CFU ml−1) and incubated at 35 °C with 160 rpm shaking for 4 days to observe dark melanin pigment (Wang et al 2015)
In the nutrient agar with L-tyrosine as a substrate, the dark pigmented melanin was observed after 3–4 days (Fig. S1)
Summary
Dietzia genus is an actinobacterium consuming many compounds, tyrosine is the sole carbon source for producing melanin pigment (Koerner et al 2009). Melanin pigment is a dark- or black-brown irregular negatively charged hydrophilic complex polymer It is produced by oxidative polymerization of phenolic or indolic compounds in various organisms (Plonka and Grabacka 2006). The carboxyl, phenolic, hydroxyl, and amine groups on melanin pigments provide numerous potential binding sites for interacting with other molecules (Hoa et al 2017). For this reason, melanins have some important properties including antitumor, antimicrobial, and antivenin activities. Response surface methodology (RSM) is a set of mathematical methods with several independent variables (Surwase et al 2012)
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