Natural Melanin Produced by the Endophytic Bacillus subtilis 4NP-BL Associated with the Halophyte Salicornia brachiata

Abstract

Natural melanin with many interesting properties has potential applications in cosmetics, drug delivery, semiconductors, etc. However, conventional production methods are not efficient, resulting in its high cost (350−650 USD g −1 ), which has been a bottleneck for its efficient commercial utilization. To explore a faster extraction method with a higher yield, a melanin-producing endophytic bacterium was isolated from the halophyte Salicornia brachiata and further identified as Bacillus subtilis 4NP-BL by phylogenetic analysis of 16S rRNA gene sequences. The maximum melanin yield of up to 1.5 g dry wt L −1 of production media was obtained through central composite design (CCD). The isolated melanin belonged to the eumelanin class with an irregular structure on the basis of elemental analysis, UV−vis, Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), electron paramagnetic resonance (EPR), and NMR studies. Furthermore, purified melanin displayed antioxidant activity and antimicrobial activity against pathogens Xanthomonas campestris and Alteromonas macleodii. Thus, this study further suggests a probable role of endophytes that produce melanin in aiding host plant protection from environmental stress and other pathogens.

Whey Protein Concentrate/Isolate Biofunctional Films Modified with Melanin from Watermelon (Citrullus lanatus) Seeds

“…The molecular structure of melanins includes multiple different reactive functional groups (−OH, −NH, and −COOH) [21]. They can be obtained and have been characterized by a variety of natural sources, including animals, plants, bacteria, and fungi [10,11,33,34]. Importantly, melanins are multifunctional and biologically-active, natural macromolecules and can be characterized as antioxidant, radioprotective, thermo-regulative, chemoprotective, antitumor, antiviral, antimicrobial, immunostimulating and/or anti-inflammatory [10,32,[34][35][36].…”

“…Importantly, melanins, like biopolymers, are obtained from renewable resources and are non-toxic; these two features make their use "greener" than many existing commercial additives [35]. Importantly, large-scale production of melanins by microorganisms digesting food waste, as well as by sustainable extraction from natural plant-residues (e.g., watermelon seeds) have been demonstrated [10,11,34]. In fact, melanin from watermelon seeds has been shown to have antioxidant and UV-barrier properties [10].…”

A Facile Alternative Sustainable Process for the Extraction and Purification of Microbial Melanin

“…10 The ratio of A650/A500 helps to calculate the amount of eumelanin in the total melanin. 23 The ratio A650/A500 was calculated to be 0.35 and indicated that extracted melanin was belonging to eumelanin class whereas, a ratio below 0.15 is observed for pheomelanin.…”

“…The effect of the medium components on melanin production was quantified by measuring the absorbance of the respective culture supernatants at 400 nm. 23…”

“…Various studies have reported that the yield of microbial melanin is significantly influenced by the nutrient components and culture conditions. [10][11][12]23,30 Melanin production was reported to be greatly influenced by tyrosine as nitrogen source in case of S. lusitanus DMZ-3. 30 In addition, yeast and beef extract were used as nitrogen sources for melanin production.…”