Mn²⁺ Alters Peroxidase Profiles and Lignin Degradation by the White-Rot Fungus Pleurotus ostreatus Under Different Nutritional and Growth Conditions

Abstract

The white-rot fungus Pleurotus ostreatus produces two types of extracellular peroxidases: manganese-dependent peroxidase (MnP) and versatile peroxidase (VP). The effect of Mn2+ on fungal growth, peroxidase activity profiles, and lignin degradation by P. ostreatus was studied in liquid culture and under solid-state fermentation conditions on perlite, the latter resembling the natural growth conditions of this fungus. The fungus was grown in either a defined asparagine-containing basidiomycete selective medium (BSM) or in a rich peptone medium (PM). Biomass production, as determined by respiration experiments in solid-state fermentation and liquid cultures and fungal growth on Petri dishes, was higher in the PM than in the BSM. Mn2+ affected biomass production only in the PM on Petri dishes. In the nonamended PM, high levels of MnP and VP activity were detected relative to the nonamended BSM. Nevertheless, a higher rate of 14C-lignin mineralization was measured in the Mn2+-amended BSM, as determined during the course of 47 d of fermentation. Mn2+ amendment of the PM increased mineralization rate to that obtained in the Mn2+-amended BSM. The enzyme activity profiles of MnP and VP were studied in the BSM using anion-exchange chromatography. In the nonamended BSM, only minute levels of MnP and VP were detected. On Mn2+ amendment, two MnP isoenzymes (B1 and B2) appeared. Isoenzyme B2 was purified and showed 100% identity with the MnP isoenzyme purified in our previous study from PM-solid-state fermentation (P6). P6 was found to be the dominant isoenzyme in terms of activity level and gene expression compared with the VP isoenzymes. Based on these results, we concluded that Mn2+ plays a key role in lignin degradation under different nutritional and growth conditions, since it is required for the production of MnP in P. ostreatus.

Lignolytic enzymes produced by Trametes villosa ccb176 under different culture conditions

“…Mn 2+ is considered to be a mediator, inducer or substrate of MnP, but its role in the expression of ligninolytic enzymes by basidiomycetes is controversial. For many of these fungi such as P. chrysosporium and P. ostreatus the presence of this metal in the culture medium is important for the production of MnP (5,25). However, Mn 2+ was not necessary for the production of MnP by P. ostreatus or Bjerkandera sp.…”

Redundancy among Manganese Peroxidases in Pleurotus ostreatus

“…Even though there is structural resemblance among mnp genes, the marked upregulation of mnp3, combined with the enhanced capabilities to degrade lignin and recalcitrant anthropogenic compounds, observed due to amendment of Mn 2ϩ to the P. ostreatus culture, suggested a central role for MnP3 in substrate utilization by this fungus. It has therefore been the center of attention of studies concerning the ligninolytic system of P. ostreatus (7,10,15,(18)(19)(20)(21)(22)25). In a previous study Salame et al (10) showed that gene silencing targeted at mnp3 resulted in the cosilencing of the entire MnP gene family, which correlated to reduced OII decolorization capacity in Mn 2ϩ -amended GP culture (10,11).…”

“…In parallel, gene expression analysis showed that Mn 2ϩ amendment results in a drastic increase in the transcript levels of the predominantly expressed genes mnp3 and mnp9 (while transcription of mnp4 was reduced), suggesting that the two corresponding short MnPs play significant roles in these processes (10,12,13,(18)(19)(20).…”

“…Previous studies have shown that Mn 2ϩ amendment to P. ostreatus growth media enables Mn 2ϩ -mediated decolorization of the azo dye orange II (OII) and increases fungal lignin degradation capacity (10,13,(18)(19)(20)(21). In parallel, gene expression analysis showed that Mn 2ϩ amendment results in a drastic increase in the transcript levels of the predominantly expressed genes mnp3 and mnp9 (while transcription of mnp4 was reduced), suggesting that the two corresponding short MnPs play significant roles in these processes (10,12,13,(18)(19)(20).…”

“…However, direct evidence linking a specific mnp to the various enhanced lignocellulose and xenobiotic degradative activities observed under Mn 2ϩ -amended culture conditions (10,13,(18)(19)(20)(21)(22)) has yet to be provided. Here, we have studied the functionality of the predominantly expressed MnPs, focusing on characterization of ⌬mnp3 strains.…”