The structural complexity of pyomelanin impacts UV shielding in Pseudomonas species with different lifestyles

Abstract

Pyomelanin, a polymeric pigment in Pseudomonas, arises mainly from alterations in tyrosine degradation. The chemical structure of pyomelanin remains elusive due to its heterogeneous nature. Here, we report strain-specific differences in pyomelanin structural features across Pseudomonas using PAO1 and PA14 reference strains carrying mutations in hmgA (a gene involved in pyomelanin synthesis), a melanogenic P. aeruginosa clinical isolate (PAM), and amelanogenic P. extremaustralis (PexM). UV spectra showed dual peaks forPAO1 and PA14 mutants and single peaks for PAM and PexM. FTIRphenol : alcohol ratio changes and complex NMR spectra indicated non-linearpolymers. UVC radiation survival increased with pyomelanin addition, correlatingwith pigment absorption attenuation. P. extremaustralis UVC survivalvaried with melanin source, with PAO1 pyomelanin being the most protective.These findings delineate structure-based pyomelanin subgroups, having distinctphysiological effects.