Regulation of peroxidase transcript levels in liquid cultures of the ligninolytic fungus Pleurotus eryngii

A versatile peroxidase able to oxidize Mn2+ as well as phenolic and nonphen olic aromatic compounds is produced in peptone-containing liquid cultures o f Pleurotus eryngii encoded by the gene mnpl. The regulation of its transcr ipt levels was investigated by Northern blotting of total RNA, High-peroxid ase transcripts and activity were found in cultures grown in glucose-pepton e medium, whereas only basal levels were detected in glucose-ammonium mediu m, The addition of more than 25 mu M Mn2+ to the former medium did not resu lt in detectable peroxidase transcripts or activity. Potential regulators w ere also added to isolated mycelium. In this way, it was shown that high tr anscript levels (in peroxidase-expressing mycelium) were maintained on pept one, whereas expression was not induced in short-term incubation experiment s. Similar results were obtained with Mn2+ ions. Strong induction of mnpl e xpression was caused by exogenous H2O2 or by continuous H2O2 generation dur ing redox cycling of menadione, By the use of the latter system in the pres ence of Fe3+, which catalyzes the reduction of H2O2 to hydroxyl radical, it was shown for the first time that the presence of this strong oxidant caus es a rapid increase of the transcripts of a ligninolytic peroxidase, In con clusion, peptone and Mn2+ affect the levels of transcripts of this versatil e peroxidase in culture, and reduced oxygen species induce short-term expre ssion in isolated mycelium, probably via a stress response mechanism.