Iris pseudacorus as an easily accessible source of antibacterial and cytotoxic compounds

Abstract

Iris pseudacorus is one of the most widespread iris species and possesses complex secondary metabolites. Our study showed that its rhizomes are abundant with phenolic compounds of which 80 % belong to the tannin group. Methanolic extracts from garden cultured iris rhizomes possessed antibacterial activity against human Gram positive Staphylococcus aureus and Enterococcus faecalis and Gram negative Pseudomonas aeruginosa and Klebsiella pneumoniae pathogens including clinical isolates resistant to commercially available antibiotics. Moreover the extract from rhizome, in concentration 3.125 mg dry weight/mL, containing gallocatechin (1), effectively combats S. aureus biofilm. The same rhizome extract acts against human cancer cell lines, especially against estrogen positive MCF-7 breast cancer cell line (IC₅₀ = 11.75 μg/mL). In vitro culture of excised, anatomical roots of I. pseudacorus excreted three antistaphylococcal compounds into the plant medium, detected by using TLC-overlayer bioautography. By the use of HPLC-DAD-ESIMS system 2 active compounds were identified as 5,7,4'-trihydroxy-6,3'-dimethoxy-isoflavone (7) and unknown dimethoxy-dihydroxy-isoflavone (9). I. pseudacorus as a non-edible plant might be considered to be new, easy accessible, non-wood source of biologically active polyphenolics.

Keywords: Excised root culture; Overlayer bioautography; Secondary metabolite; Tannins; Yellow flag iris.