Regulation of Peroxidase Transcript Levels in Liquid Cultures of the Ligninolytic Fungus Pleurotus eryngii

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American Society for Microbiology

RESUMO

A versatile peroxidase able to oxidize Mn2+ as well as phenolic and nonphenolic aromatic compounds is produced in peptone-containing liquid cultures of Pleurotus eryngii encoded by the gene mnpl. The regulation of its transcript levels was investigated by Northern blotting of total RNA. High-peroxidase transcripts and activity were found in cultures grown in glucose-peptone medium, whereas only basal levels were detected in glucose-ammonium medium. The addition of more than 25 μM Mn2+ to the former medium did not result in detectable peroxidase transcripts or activity. Potential regulators were also added to isolated mycelium. In this way, it was shown that high transcript levels (in peroxidase-expressing mycelium) were maintained on peptone, whereas expression was not induced in short-term incubation experiments. Similar results were obtained with Mn2+ ions. Strong induction of mnpl expression was caused by exogenous H2O2 or by continuous H2O2 generation during redox cycling of menadione. By the use of the latter system in the presence 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 causes a rapid increase of the transcripts of a ligninolytic peroxidase. In conclusion, peptone and Mn2+ affect the levels of transcripts of this versatile peroxidase in culture, and reduced oxygen species induce short-term expression in isolated mycelium, probably via a stress response mechanism.

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