EPR spectroscopy was used to examine the properties of and free radical concentrations in atypical water-soluble melanin-like pigments from Bacillus weihenstephanensis strains. The same EPR spectral shape was observed in bacterial melanins as in eumelanin. The EPR lines were homogeneously broadened. Continuous microwave saturation of the EPR lines indicated slow spin-lattice relaxation processes in the samples. Strong dipolar interactions characterized the tested melanin samples. Higher free radical concentrations were found in bacterial melanin than in synthetic melanin. The free radical concentrations in melanin from B. weihenstephanensis increased in the following order: strain JAS 81/4 < JAS 83/3 < JAS 86/1 < JAS 39/1. (C) 2017 Elsevier B.V. All rights reserved.