Bio-economics of melanin biosynthesis using electromagnetic field resistant Streptomyces sp.-EF1 isolated from cave soil

Moving charges due to electric current create electromagnetic waves, which generate electromagnetic fields (EMFs). The low frequency EMFs are unlikely to cause adverse effects on living organisms; however, health-related incidents have prompted researchers to investigate the biochemical characteristics in microorganisms. We hypothesized that a diverse variety of microorganisms, i.e., bacteria, will respond to EMF and bio-stimulate microbial metabolic products of commercial significance. An EMF generator that produces a 10-mT-strength magnetic field was built in-house to investigate the magnetic response of microbial communities from cave soil samples. 16S rRNA sequencing was employed to identify three EMF-responsive isolates: Streptomyces sp., Arthrobacter sp., and Lysinibacillus sphaericus, designated as EF1, EF2, and EF3, respectively. Streptomyces sp.-EF1 showed a dark brown pigment identified as melanin on nutrient agar plates supplemented with 0.4 % L-tyrosine and L-DOPA. We also investigated the bio-economics of melanin biosynthesis, which revealed that waste shredded paper ($33.29 /g melanin) followed by starch ($256.03 /g melanin) were among suitable substrates for melanin biosynthesis under non-EMF condition. The most time-efficient melanin formation was achieved by starch under submerged fermentation (3.52 h/μg/mL) conditions. Shredded, laser-printer paper was noticed to be a cost-efficient process ($33.29 /g melanin) for melanin biosynthesis.