Department of Plant Pathology and Microbiology, The Hebrew University of Jerusalem, The Robert H. Smith Faculty of Agriculture, Food & Environment, Rehovot
The use of white rot fungi such as Pleurotus ostreatusand their lignin-modifying enzymes has become an effective treatment for the degradation of wide range of natural and xenobiotic aromatic compounds.Themanganese peroxidasegene family (mnps) is a main part of the ligninolytic system ofP. ostreatus.This genefamily is comprised of nine members,mnp1-9,encoding short manganese peroxidases (short-MnPs) or versatile short-MnPs (VPs).We show that unlike in Mn2+amended glucose-peptone (GP) medium, where redundancy amongmnpswas reported, in Mn2+-deficient GPmnp4(encoding VP4) has a key and non-redundant function.The abundance ofmnpstranscripts at time points corresponding to the tropophase (active growth), early idiophase and idiophaseindicatethatmnp4is thepredominantly expressedmnpgene and thatitsrelative predominanceisdependent on culture age.In this medium,thedecolorizationof the azo dye Orange IIoccurs only during the idiophase and a Δmnp4strainshowed a drastic reduction in this decolorization.Threedegradation metabolites wereidentifiedby LC-MS indicating both asymmetric and symmetric enzymatic cleavage of the azo bond.In addition,the culture filtrate of Δmnp4showed negligible values ofoxidation capability of four typical VP substrates: Mn2+,2,6-dimethoxyphenol,Phenol red and Reactive black 5, compared to the PC9 (wild type). We concluded thatunder Mn2+-deficient GP culture, VP4 is the main active ligninolytic enzyme able to oxidizeMn2+as well as high and low redox potential aromatic substrate, including dyes. Furthermore, other VPs/MnPs do not compensate for the lack of VP4 activity.
