Abstract
Putative iron-reductase (IR) genes from Serpula lacrymans with similarity to the conserved iron-binding domains of cellobiose dehydrogenase (CDH) enzymes have been identified. These genes were cloned and expressed to functionally characterize their activity and role in the decomposition of lignocellulose. The results show that IR1 and IR2 recombinant enzymes have the ability to depolymerize both lignin and cellulose, are capable of the reduction of ferric iron to the ferrous form, and are capable of the degradation of nitrated lignin. Expression of these genes during wheat straw solid-state fermentation was shown to correlate with the release of compounds associated with lignin decomposition. The results suggest that both IR enzymes mediate a non-enzymatic depolymerisation of lignocellulose and highlight the potential of chelator-mediated Fenton systems in the industrial pre-treatment of biomass.
Highlights
Biorefineries capable of the production of renewable chemicals from a range of suitable biomass feedstocks have been proposed as the basis for a biobased economy [1, 2]
Cloning of iron reductase from the brown rot fungus Serpula lacrymans. To clone both genes (IR1 and IR2), primers were designed for the full length coding sequence (CDS), and the genes amplified from cDNA prepared from total RNA extracted from 41 days culture of Serpula lacrymans grown on wheat straw (Table 2)
While the data demonstrate that the potential of both IR proteins facilitates reactions that depolymerize the polymers found in lignocellulose, full elucidation of their role requires further study
Summary
Biorefineries capable of the production of renewable chemicals from a range of suitable biomass feedstocks have been proposed as the basis for a biobased economy [1, 2]. 2,3 dihydroxybenzoic acid (DHBA) was reported as the chelating agent [12] released by the brown rot fungi Gloeophyllum trabeum [19] which is able to promote sustained iron reduction and generate reactive oxygen species (ROS). This suggests that the CMF reaction could become a self-sustaining process; it is unclear how the process is initiated. Recombinant S. lacrymans IR1 and IR2 proteins were produced using gateway plasmids cloned in E. coli The function of these proteins was tested for their iron reduction capabilities and the ability to release sugars and phenolic compounds through a putative chelator-mediated Fenton attack on lignocellulose. The results help to explain the particular ability of this brown rot fungus to degrade lignocellulose, and their potential as tools for the pretreatment of biomass
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