Melanin-Like Pigment Synthesis by Soil Bacillus weihenstephanensis Isolates from Northeastern Poland

Although melanin is known for protecting living organisms from harmful physical and chemical factors, its synthesis is rarely observed among endospore-forming Bacillus cereus sensu lato. Here, for the first time, we reported that psychrotolerant Bacillus weihenstephanensis from Northeastern Poland can produce melanin-like pigment. We assessed physicochemical properties of the pigment and the mechanism of its synthesis in relation to Bacillus weihenstephanensis genotypic and phenotypic characteristics. Electron paramagnetic resonance (EPR) spectroscopy displayed a stable free radical signal of the pigment from environmental isolates which are consistent with the commercial melanin. Fourier transform infrared spectroscopy (FT-IR) and physicochemical tests indicated the phenolic character of the pigment. Several biochemical tests showed that melanin-like pigment synthesis by Bacillus weihenstephanensis was associated with laccase activity. The presence of the gene encoding laccase was confirmed by the next generation whole genome sequencing of one Bacillus weihenstephanensis strain. Biochemical (API 20E and 50CHB tests) and genetic (Multi-locus Sequence Typing, 16S rRNA sequencing, and Pulsed-Field Gel Electrophoresis) characterization of the isolates revealed their close relation to the psychrotrophic Bacillus weihenstephanensis DSMZ 11821 reference strain. The ability to synthesize melanin-like pigment by soil Bacillus weihenstephanensis isolates and their psychrotrophic character seemed to be a local adaptation to a specific niche. Detailed genetic and biochemical analyses of melanin-positive environmental Bacillus weihenstephanensis strains shed some light on the evolution and ecological adaptation of these bacteria. Moreover, our study raised new biotechnological possibilities for the use of water-soluble melanin-like pigment naturally produced by Bacillus weihenstephanensis as an alternative to commercial non-soluble pigment.