Cinnabarinic Acid Accumulation by Pycnoporus cinnabarinus in Three Submerged Culture Systems and Bacterial Growth-Inhibitory Activity of the Crude Extracts

Abstract

Cinnabarinic acid (CA) is a phenoxazinone metabolite produced by Pycnoporus fungi and reported to have antibacterial activity. This study compared CA production by Pycnoporus cinnabarinus HEMIM-53 in three culture systems, Shake flasks (FSK), a Stirred-tank reactor (STR), and an airlift reactor (ALR), together with the bacterial growth-inhibitory activity (BGIA) of the crude extracts against Escherichia coli and Staphylococcus aureus. In Petri dishes, radial growth was favored at pH 5.5–7.5, with the highest mycelial density at pH 6.5 and pigmentation at pH 8.5. In submerged cultures, the systems differed markedly in glucose consumption, pH profiles, mycelial morphology, and extracellular laccase activity. Although FSK and STR showed higher laccase activity, HPLC quantification of CA and 3-hydroxyanthranilic acid (3-HAA) revealed the highest final CA concentration in the ALR, indicating that CA accumulation was not proportional to total laccase activity. ALR extracts also produced growth inhibition of both bacteria, whereas FSK extracts produced the weakest. Because the systems differed in scale, aeration, agitation and instrumentation, and the extracts differed in pH and composition, these effects cannot be attributed to the culture configuration or to CA alone. This descriptive comparison provides a basis for controlled studies with matched operating conditions, pH-adjusted and uninoculated-medium controls, and purified CA.