Objective
- White rot fungi are unique organisms capable of oxidising lignin, which is a heterogeneous aromatic biopolymer. These fungi possess a complex extracellular enzyme machinery composed of peroxidases, hydrogen peroxide producing oxidases, low molecular weight cofactors (Mn, organic acids, secondary metabolites). This enzyme system is responsible for the initial oxidation of lignin. Since these reactions are non-selective, many other aromatic compounds such as polycyclic aromatic hydrocarbons (PAH), dioxins, azo dyes, etc. can be oxidised by white rot fungi. Consequently, white rot fungi are being considered for applications in the clean-up of organopollutant contaminated sites and in wastewater treatment of different industries;
- The objectives of the project are to determine the crucial physiological factors for increased peroxidase production in two white rot fungal strains, Bjerkandera sp. strain B0S55 and Phanerochaete chrysosporium. The overproduction of the main two peroxidases of these trains, namely lignin peroxidase (LiP) and manganese-dependent-peroxidase (MnP) was attempted by identifying and manipulating important physiological signals responsible for their expression. This knowledge was used to sustain their continuous production by fungi immobilised in bioreactors.
- In Bjerkandera sp. strain B0S55, both LiP and MnP could be overproduced in nitrogen-sufficient liquid cultures. MnP was stimulated the most by applying 100 to 500 uM of Mn, a pH of 5.2 and supplementing the medium with organic acids (i.e. 5 mM glycolate). LiP production was greatly enhanced in the absence of Mn due to the inhibitory effect of Mn on veratryl alcohol biosynthesis, a secondary metabolite needed to stabilise LiP activity;
- In Phanerochaete chrysosporium, overproduction of LiP was observed in nitrogen-sufficient unsubmerged cultures where the mycelium is immobilised on polyurethane foam blocks. The mechanism of LiP induction was found to be related to oxygen radicals, the highest LiP production was observed under an oxygen atmosphere. Mn reduced LiP production since it stimulated Mn-dependent superoxide dismutase that reduced the exposure of the fungus to oxygen radicals. A unique enzyme was discovered that dephosphorylates LiP isozymes, creating new LiP isozymes;
- Continuous production of lighinolytic enzymes by Phanerochaete chrysosporium in bioreactors with mycelium immobilised on foam blocks or as pellets was feasible for long periods of time (more than 140 days). A key design feature required for long term operation is the use of a pulsed air reactor that prevents conglomeration of mycelium pellets and subsequent clogging of the reactor. The ideal condition for the continuous production of LiP was the use of an oxygen gas-phase instead of air. The ideal condition for MnP was the use of a medium that contained 5000 uP of Mn.
Topic(s)
Data not availableCall for proposal
Data not availableFunding Scheme
CSC - Cost-sharing contractsCoordinator
6703 HD Wageningen
Netherlands