Enhanced Streptomyces roseochromogenes melanin production by using the marine renewable source Posidonia oceanica egagropili

Since the possibility to biotechnologically produce melanin by Streptomycetes using plant biomass has been so far poorly investigated, Posidonia oceanica egagropili, a marine waste accumulating along the Mediterranean Sea coasts, was explored as a renewable source to enhance extracellular melanin production by Streptomyces roseochromogenes ATCC 13400. Therefore, different amounts of egagropili powder were added to a culture medium containing glucose, malt extract, and yeast extract, and their effect on the melanin biosynthesis was evaluated. A 2.5 g center dot L-1 supplementation in 120-h shake flask growths at 26 degrees C, at pH 6.0 and 250 rpm, was found to enhance the melanin production up to 3.94 +/- 0.12 g center dot L-1, a value 7.4-fold higher than the control. Moreover, 2-L batches allowed to reach a concentration of 9.20 +/- 0.12 g center dot L-1 in 96 h with a productivity of 0.098 g center dot L-1 center dot h(-1). Further studies also demonstrated that the melanin production enhancement was due to the synergistic effect of both the lignin carbohydrate complex and the holocellulose components of the egagropili. Finally, the pigment was purified from the broth supernatant by acidic precipitation and reversed-phase chromatography, characterized by UV absorbance and one- and two-dimensional NMR, and also tested for its chemical, antioxidant, and photo-protective properties.

Automated summary

This study explored the potential of using Posidonia oceanica egagropili, a marine waste, as a renewable source to enhance extracellular melanin production in Streptomyces roseochromogenes ATCC 13400. It was found that adding egagropili powder to the culture medium significantly increased melanin biosynthesis, and further investigation revealed that this enhancement was due to the synergistic effect of lignin carbohydrate complex and holocellulose components in egagropili.