Transcript and activity levels of different Pleurotus ostreatus peroxidases are differentially affected by Mn2+

The white-rot fungus Pleorotus ostreatus produces both manganese-dependent peroxidase (MnP) and versatile peroxidase (VP) in non-manganese-amended pep tone medium (PM). We studied the effect of Mn2+ supplementation on MnPs and VPs in P. ostreatus by analysing the enzymatic and transcript abundance pr ofiles of the peroxidases, as well as the lignin mineralization rate. The f ungus was grown in PM under solid-state conditions using perlite as an iner t solid support. Mn2+ amendment resulted in a 1.7-fold increase in [C-14]-l ignin mineralization relative to unamended medium. Anion-exchange chromatog raphy was used to resolve the fungal peroxidase's enzymatic activity profil e. Five peaks (P1-P5) of VP and one peak (P6) of MnP activity were detected in unamended medium. In Mn2+-amended medium, a reduction in the activity o f the VPs was observed. On the other hand, a sharp increase in the MnP acti vity level of peak P6 was detected. The P6 isoenzyme was purified and showe d manganese-dependent peroxidation of phenolic substrates. Internal sequenc e analysis of the purified enzyme revealed 100% identity with the deduced a mino acid sequence of P. ostreatus MnP3 (GenBank AB016519). The effect of M n2+ on the relative abundance of gene transcripts of three VPs and one MnP from P. ostreatus was monitored using reverse transcription-polymerase chai n reaction (RT-PCR) with oligonucleotide primer sets synthesized on the bas is of non-conserved sequences of the different peroxidases. The reduction i n VP gene transcript abundance and the increase in mnp3 transcript level we re collinear with the changes observed in the enzyme activity profiles. The se results indicate that the activity of peroxidases is regulated at the tr anscriptional level. We suggest that the expression of MnP and VP may be di fferentially regulated by the presence of Mn2+.