Aspergillus niger as a cell factory for the production of pyomelanin, a molecule with UV-C radiation shielding activity

Kurzfassung

Melanins are complex pigments with numerous biological functions that have potential applications in space exploration and biomedicine due to their radioprotective properties. Aspergillus niger is, a fungus with naturally high radiation resistance, is well established as a biotechnologically harnessed cell factory, and is an eligible candidate for melanin production. Within this study, we demonstrate that A. niger can produce a radioprotective fungal pyomelanin (PyoFun) via L-tyrosine inducible overproduction in a recombinant ΔhmgA mutant strain (OS4.3). PyoFun as well as a synthetic pyomelanin (PyoSyn) control were extracted and purified for further characterisation and radiation shielding capacities. The production sequence for pyomelanin from OS4.3 has not yet been optimized for a large upscaled production but the average PyoFun yield extracted from a 200 mL culture of OS4.3 has shown an excellent bioconversion rate from L-tyrosine as a precursor. The characterization was succesfully performed using three spectroscopic methods (UV-Vis, FTIR and RAMAN spectroscopy) as well as physiochemical tests. Furthermore, its strong antioxidant properties were assessed with DPPHassays. Additionally, the study evaluated the protective effect of PyoFun and PyoSyn against nonionizing radiation (monochromatic UV-C) and displayed a significant protective effect against the radiation induced stress for UV-C dosages in the range of space surroundings (1038 J/m²). Here, PyoFun also demonstrated superior protection compared to the synthetically produced control pyomelanin (PyoSyn). These findings suggest that PyoFun has significant potential as a biological shield against harmful radiation, particularly for the research field of in - situ resource utilisation (ISRU) for future space exploration settings, since the generated pyomelanin is synthesized extracellularly and there is no need for cell lysis for pigment purification. Although the pigments have only been assessed in dissolved form so far, further research is necessary to test them in a dried form, similar to how melanin pigments are found in nature. However, the findings of this study show that pyomelanin could be a valuable biological derived agent for shielding human tissue and coat materials against harmful radiation, highlighting the significance of further exploration in this area, since in all human space travel endeavours harmful radiation protection is an ongoing and crucial element of research.