Differences in the secretion pattern of oxidoreductases from Bjerkandera adusta induced by a phenolic olive mill extract

The secretome of the white-rot fungus Bjerkandera adusta produced in synthetic Kirk medium was compared to that supplemented with an aqueous phenol-rich extract of dry olive mill residues (ADOR). Distinct changes in the protein composition of oxidoreductases, namely diverse class-II peroxidases and aryl alcohol oxidases were found. In the ADOR-supplemented medium (ASC), 157 distinct proteins were identified by the secretome analysis, whereas only 59 of them were identified without ADOR supplementation (Kirk medium culture; KM). Proteome analysis indicated that the number of peroxidases produced in ASC was more than doubled (from 4 to 11) compared to KM. Two short manganese peroxidases (MnP1 and MnP6) and one versatile peroxidase (VP1) represented 29% of the relative abundance (NSAF) in ASC. Two of them (MnP1 and VP1) were also detected in KM at a relative abundance (NSAF) of only 3%. Further peroxidases present in ASC were one lignin peroxidase (LiP2), one generic peroxidase (GP) and three dye-decolorizing peroxidases (DyPs). The relative abundance of DyPs and aryl alcohol oxidases (AAO) were lower in ASC in comparison to KM. In addition to peptide sequence analysis, the secretion of Mn2+-oxidizing peroxidases as well as AAOs were followed by enzyme measurement. The Mn2+-oxidizing activity increased nearly 30-fold (from 10 to 281 Ul(-1)) after ADOR addition. Two enzymes responsible for that activity were successfully purified (BadVPI and BadVPII). To prove a potential involvement of these enzymes in the degradation of aromatic compounds, BadVPI was tested for its ability to degrade the recalcitrant dehydrogenated polymer (DHP, synthetic lignin). These results show that natural phenol-rich materials act as secretome-stimulating additives. Applying these substances enables us to investigate fungal degradation and detoxification processes and gives more insight into the complexity of fungal secretomes, e.g. of white-rot fungi. (C) 2014 Elsevier Inc. All rights reserved.