A new paper published in the journal Biotechnology for Biofuels and Bioproducts by the group led by Dr. Susana Camarero at the Centro de Investigaciones Biológicas Margarita Salas (CSIC) shows the production of a set of new fungal laccases capable of operating under the extreme conditions of high temperature and pH typical of industrial wood processing into kraft pulp or fibreboard.
The pulp and paper industry faces the challenge to achieve the full exploitation of all wood components to become integrated biorefineries. During kraft pulping, the predominant process to produce chemical pulp from wood, lignin is removed, released in the black liquors, and usually incinerated to obtain energy for the mill. However, lignin possesses attractive chemical properties as a bulk polymer and constitutes a valuable source of renewable aromatic compounds. Depolymerization of kraft lignins into phenolic building blocks to replace fossil-derived chemicals constitutes a main breakthrough in valorizing these industrial lignins into sustainable products. In addition, more environmentally sound and sustainable means of production are sought in industrial wood processing.
Through enzyme engineering combining enzyme-directed evolution and rational design, Rodríguez-Escribano and co-workers have developed and produced in yeast a set of extremophilic ligninolytic oxidases (laccases) that are capable to operate at extreme conditions of pH and temperature. For the first time, fungal laccases of high-redox potential are able to oxidize lignin-derived phenols and kraft lignin at pH 10, something unbelievable for the wild-type enzymes that have strong acidic activity. Besides, the new laccases show maximum activities at 70ºC and remarkable thermal resistance.
The applicability of the new tailor-made laccases is demonstrated by their ability to depolymerize kraft lignins which are only soluble at alkaline pH. Moreover, they improve the bleachability of kraft pulps, reducing the need for chlorine dioxide compared to the industrial bleaching procedure. Additionally, they reduce the energy required to obtain fibers from wood chips in fiberboard manufacture. Their use as biocatalysts in the wood conversion sector is expected to support the development of more environmentally sound and efficient processes, and more sustainable products.
The results published in this paper were obtained in the framework of the WoodZymes project which aimed to provide extremophilic biocatalysts capable of valorizing biomass side-streams from kraft pulp production, and extremozyme-aided processes to reduce the energy and chemicals required in paper pulp and fiberboard production.
The work is the result of an international collaboration between the CIB Margarita Salas, the Sapienza Università di Roma, the Biotech SME MetGen Oy (Finland), the Centre Technique du Papier (France), and the FCBA Institut Technologique (France).
Reference: Tailor-made alkaliphilic and thermostable fungal laccases for industrial wood processing. David Rodríguez‐Escribano, Rocío Pliego‐Magán, Felipe de Salas, Pablo Aza, Patrizia Gentili, Petri Ihalainen, Thomas Levée, Valérie Meyer, Michel Petit‐Conil, Sandra Tapin‐Lingua, Michael Lecourt, Susana Camarero (2022) Biotechnology for Biofuels and Bioproducts. 15, 149. https://doi.org/10.1186/s13068-022-02247-2