Thermal and mass spectroscopic characterization of a sulphur-containing bacterial melanin from Bacillus subtilis

Among technologies for melanin commercial-scale production, microbial synthesis is an attractive option. In this study, a melanin producer, wild strain Bacillus subtilis, was isolated from the soil, and pigment from this bacterium was purified and characterised using different techniques. The use of tandem pyrolysis/gas chromatography/mass spectrometry allowed us to classify the pigment as a sulphur-containing bacterial melanin. Thermogravimetric and differential thermal analyses indicated that melanin might contain two fractions of water, a strongly bound fraction and a weakly-bound fraction. Scanning electron microscopy showed an amorphous structure without differential characteristics, and electronic conductivity measurements at normal atmospheric conditions and humidities suggest that melanin may be an insulator. However, more work is underway to clarify this point.