|HILDEBRAND, AMANDA - University Of California
|FAN, ZHILIANG - University Of California
Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/26/2015
Publication Date: 4/7/2015
Publication URL: http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0123006
Citation: Hildebrand, A., Kasuga, T., Fan, Z. 2015. Production of cellobionate from cellulose using an engineered Neurospora crassa strain with laccase and redox mediator addition. PLoS One. DOI: 10.1371/journal.pone.0123006.
Interpretive Summary: Both plant pathogenic fungi and oomycetes produce phenolics-degrading enzymes called Laccases. The enzymes have been suggested to involve in pathogenicity through oxidizing lignin in plant cells. In this report, we characterized a laccase from a plant pathogen Neurospora crassa, characterized gene regulation and explored the use of laccases for the production of fermentable sugars from cellulosic material for biofuel production.
Technical Abstract: We report a novel production process for cellobionic acid from cellulose using an engineered fungal strain with the exogenous addition of laccase and a redox mediator. A previously engineered strain of Neurospora crassa (F5'ace-1'cre-1'ndvB) was shown to produce cellobionate directly from cellulose without the addition of exogenous cellulases. Specifically, N. crassa produces cellulases, which hydrolyze cellulose to cellobiose, and cellobiose dehydrogenase (CDH), which oxidizes cellobiose to cellobionate. However, the conversion of cellobiose to cellobionate is limited by the slow re-oxidation of CDH by molecular oxygen. By adding low concentrations of laccase and a redox mediator to the fermentation, CDH can be efficiently oxidized by the redox mediator, with in-situ re-oxidation of the redox mediator by laccase. The conversion of cellulose to cellobionate was optimized by evaluating pH, buffer, and laccase and redox mediator addition time on the yield of cellobionate. Mass and material balances were performed, the use of the native N. crassa laccase in such a conversion system was evaluated against the exogenous Pleurotus ostreatus laccase.