Application of the aquatic fungus Phoma sp. (DSM22425) in bioreactors for the treatment of textile dye model effluents

Background: Textile dyes are hardly removed from effluents by conventional wastewater treatment but can be degraded by a number of physicochemical processes nevertheless having specific limitations. The development of bioremediation processes may provide a viable alternative. Results: Resting cells of three aquatic fungal strains, Alternaria sp. (Tt-S1), Coniothyrium sp. (Kl-S5) and Phoma sp. (DSM22425), were evaluated for their ability to decolorize model effluents of different dye application classes. Phoma sp., who decolorized all four applied model wastewaters (MWW), was immobilized on a polyester-based fleece material originally designed for the use as cooker-hood filters, and applied in internal loop airlift and bubble column reactors in repeated batch mode under sterile and nonsterile conditions. Depending on the applied MWW and bioreactor setup, a decolorization by more than 90 % was achieved in three consecutive treatment cycles and a total operation time of 16 days. In an upscaled reactor (10 L), Phoma sp. decolorized a MWW for acid dyes by 61 %. Chemical oxygen demand of the MWW was reduced by 36 %. Conclusion: The presented results underline the potential of aquatic fungi for the development of textile dyeing effluent treatment processes

Bioremediation of emerging pollutants using fungi - Successes and challenges

Rapid economic development in many regions of the globe has contributed to intensification of the contamination in our environment. Emerging pollutants including endocrine disruptors, pharmaceuticals and personal care products are persistent and recalcitrant to microbial attack. The ligninolytic system of white-rot fungi (WRF) consisting, among others, of laccase (E.C. 1.10.3.2) and peroxidases such as Mn peroxidase (E.C. 1.11.1.13) and lignin peroxidase (E.C. 1.11.1.14) is involved in the degradation of various xenobiotic compounds such as the above emerging contaminants. We have been investigating the biocatalytic elimination of established or suspected xenoestrogens including nonylphenol (NP), bisphenol A (BPA) and triclosan (TCS) using laccases from Coriolopsis polyzona, Lentinus critinus or Ganoderma japonicum. The enzymatic treatment produces high MW metabolites of NP, BPA and TCS (from dimers up to pentamers) which are devoid of hormone-like activity. A sequence of optimization techniques has enabled the improvement of the effluent treatment process using soluble laccase. To improve the effectiveness and re-use of the enzyme, we implemented it under solid and retainable form in appropriate bioreactors. When used in a conventional packed-bed reactor or in a novel perfusion basket reactor, support-immobilized or cross-linked insolubilized laccase was able to eliminate BPA from aqueous solutions under different operational conditions. These included several consecutive treatment cycles and even continuous processing with sustained removal performance. In addition to a critical appraisal of these developments, current and emerging biotechnological applications of fungal enzymes will highlight our research results, while the remaining challenges in mycoremediation will be addressed

Cross-linking of multi-enzyme aggregates - Combi-CLEAs of two laccases with broadened pH-spectrum

The immobilization of enzymes is one of the prerequisites for their successful application in industrial processes as it often improves desired properties such as stability. Furthermore, immobilization of enzymes facilitates their retention in reactor systems as well as their reuse. Beside carrier-based immobilization approaches, the cross-linking of enzyme aggregates (CLEAs), developed by the group of R.A. Sheldon, has gained considerable attention during the last decade. CLEAs are produced by precipitating the protein(s) of interest with a suitable precipitant (e.g. ammonium sulphate, acetone or polyethylene glycol) and subsequently link the protein aggregates covalently to each other (e.g. with a bifunctional cross-linker like glutaraldehyde). This methodology is simple, does not need highly purified enzymes and results in biocatalysts of high specific activity, solely consisting of protein. Laccases are enzymes able to oxidize a high variety of pollutants like phenols, endocrine disrupting chemicals or polycyclic aromatic hydrocarbons only needing molecular oxygen as final electron acceptor. They are thus of high interest for biotechnological applications. In our group, laccase-CLEAs have been successfully produced and applied for the treatment of endocrine disruptors in adapted reactor systems. These emerging pollutants are of concern as they pass conventional wastewater treatment plants (WWTP) and enter the environment where they can modulate or disrupt the endocrine system of animals even at very low concentrations. The EU-project MINOTAURUS is aiming at the development of intensified processes for pollutant removal based on different immobilization approaches. One of the goals is the development of an enzymatic polishing step to be applied to conventionally treated wastewaters, thus providing a viable solution for the problem of endocrine disruptors. To reach this goal, several obstacles have to be overcome. Laccases usually possess an activity-optimum in the acidic pH-range against phenolic substrates, which limits their applicability in neutral or even alkaline matrices. Here, we present first results to combine laccases from Coriolpsis polyzona, with an acidic pH-optimum, and from Coprinopsis cinerea, with a neutral pH-optimum, in a single biocatalyst. The production of combined CLEAs of both laccases was optimized. The obtained combi-CLEAs showed activity over a broad pH-range implying their suitability for the treatment of wastewaters with varying pHs. These results are promising, thus next steps will include a comprehensive characterization of the developed biocatalysts and an application in a lab-scale bioreactor system for the treatment of a real WWTP-effluent. We thank M. Ruehl from the laboratory of Prof. U. Kües - Molecular Wood Biotechnology and Technical Mycology - at the University of Göttingen, Germany, for providing the C. cinerea laccase