Laccase-catalyzed formation of cinnabarinic acid is responsible for antibacterial activity of Pycnoporus cinnabarinus.

Concentrated culture fluid of the wood-rotting basidiomycete Pycnoporus cinnabarinus showed biological activity against a variety of bacterial strains. The maximal inhibitory effect was obtained for Gram-positive bacteria of the genus Streptococcus. In general, inhibition was higher for Gram-positive than Gram-negative bacteria. P. cinnabarinus produces the phenoxazinone derivative, cinnabarinic acid. This red pigment accumulates in sporocarps as well as in liquid cultures. As shown previously, laccase secreted by the fungus oxidizes the precursor 3-hydroxyanthranilic acid to cinnabarinic acid. The present study demonstrates that this reaction is necessary for the production of antibacterial compounds by the fungus. The biological activity of concentrated P. cinnabarinus culture fluid was nearly identical with that of cinnabarinic acid, synthesized by purified laccase in vitro.