Valorisation of deinking sludge as a substrate for lignocellulolytic enzymes production by Pleurotus ostreatus

Authors: VODOVNIK, MAŠA - University Of Ljubljana; VRABEC, KATJA - University Of Ljubljana; HELLWIG, PATRICK - Otto von Guericke University; BENNDORF, DIRK - Otto von Guericke University; SEZUN, MIJA - Pulp And Paper Institute; GREGORI, ANDREJ - Mycomedica Doo; GOTTUMUKKALA, LALITHA - University Of Limerick; Anderson, Robin; REICHL, UDO - Otto von Guericke University

Submitted to: Journal of Cleaner Production
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/14/2018
Publication Date: 6/18/2018
Citation: Vodovnik, M., Vrabec, K., Hellwig, P., Benndorf, D., Sezun, M., Gregori, A., Gottumukkala, L.D., Anderson, R.C., Reichl, U. 2018. Valorisation of deinking sludge as a substrate for lignocellulolytic enzymes production by Pleurotus ostreatus. Journal of Cleaner Production. 197(1):253-263. https://doi.org/10.1016/j.jclepro.2018.06.163.
DOI: https://doi.org/10.1016/j.jclepro.2018.06.163

Interpretive Summary: The disposal of waste sludges produced in large amounts in the pulp and paper industry imposes significant environmental and economical problems on society. One strategy to address these issues is to redirect their use for the microbial production of biotechnologically relevant enzymes. In the present study, sludge produced from the deinking of recycled paper was assessed as a substrate for low-cost production of high value enzymes by 30 selected fungal strains. Based on the results of growth and activity screenings, one fungal strain named Pleurotus ostreatus PLAB was chosen as the most promising candidate, and its enzyme profile was further studied by quantitative enzyme assays and other chemical characterization methods. While P. ostreatus enzymes are active against cellulose and xylan, both important fiber components, when reacted with deinking sludge in similar fashion to enzymes from the other fungal strains, we found that P. ostreatus produced an enzyme that was significantly better at degrading another fiber component known as laccase. We further observed that this latter enzyme appears to be produced in response to a number of different components. These findings indicate that deinking sludge may be a good substrate for the low-cost fungal production of certain enzymes with broad biotechnological applications, including bioremediation in the paper and bioenergy industries thereby yielding beneficial, value-added products from otherwise wasteful materials.

Technical Abstract: Disposal of waste sludges produced in large amounts in the pulp and paper industry imposes significant environmental and economical problems on society. One strategy to address these issues involves revalorization of paper mill sludges by applying these as substrates for microbial production of biotechnologically relevant enzymes. In the following work, deinking sludge was assessed as a substrate for low-cost production of lignocellulolytic enzymes by 30 selected fungal strains. Based on the results of growth and activity screenings, Pleurotus ostreatus PLAB was chosen as the most promising candidate and its secretome was further studied by quantitative enzyme assays and mass spectrometry. While cellulase and xylanase activities detected in P. ostreatus extracts reacted with deinking sludge were similar to activities of cultures grown on other lignocellulosic substrates, average laccase activity was significantly higher (46 000 U/kg DIS). Mass spectrometry identification of the most prominent proteins in the secretome of the target strain confirmed that significant amounts of the enzymes involved in lignin degradation (laccases, manganese peroxidase, and bilirubin oxidase) were produced with this substrate despite the low lignin content in the deinking sludge, thus indicating the presence of other inducible compounds. The findings of this study suggest that deinking sludge may represent a good substrate for low-cost fungal production of certain enzymes with broad biotechnological applications, including bioremediation in the paper and bioenergy industries.