Fungal-bacterial consortia increase degradation of the phenylurea herbicide diuron in water-unsaturated systems Ellegaard-Jensen, L. 1,2 *; Knudsen, B.E. 1,2 ; Johansen, A. 3 ; Albers, C.N. 1 ; Aamand, J. 1 ; Rosendahl, S. 2 1 Department of Geochemistry, Geological Survey of Denmark and Greenland (GEUS), Øster Voldgade 10, DK-1350 Copenhagen K, Denmark 2 Department of Biology, Copenhagen University, Universitetsparken 15, DK-2100 Copenhagen Ø, Denmark 3 Department of Environmental Science, Aarhus University, Frederiksborgvej 399, DK-4000, Roskilde, Denmark * Lep@geus.dk Introduction The phenylurea herbicide diuron is found in surface- and groundwater at concentrations above the EU threshold limit of 0.1 μg l -1 (Lapworth and Gooddy, 2006; Struger et al., 2011; Torstensson, 2001), and since it has adverse effects on the environment and presumably on human health (Cox, 2003; Giacomazzi and Cochet, 2004), it is on the EU Water Framework Directive´s list of priority substances (European Parliament, 2008). In order to alleviate persistent diuron contamination in terrestrial environments, bioremediation has been suggested as a possible technology to remove diuron from soils. Consortia of selected fungi and bacteria may prove more efficient for bioremediation of pesticide polluted soils than the individual strains alone. This synergistic effect may be due to co-operative degradation where one organism transforms the compound to products which are then further transformed by the other organism (Tixier et al., 2002). In addition, fungal hyphae may function as transport vectors for bacteria thereby facilitating a more effective spreading of degrader organisms in soil (Furuno et al., 2010; Kohlmeier et al., 2005). Method We constructed several diuron-degrading consortia, combining different bacterial (Sphingomonas sp. SRS2, Variovorax sp. SRS16, and Arthrobacter globiformis D47) and fungal (Mortierella sp. LEJ702 and LEJ703) degrader strains. Several aspects of the interaction between the strains during diuron degradation were studied, including fungus- mediated bacterial transport, diuron degradation pathways, and microbial interactions affecting fungal growth. Experiments were carried out in a small column system, which we had developed, where diuron spiked sand and organisms were spatially separated by a layer of sterile glass beads. The microorganisms therefore had to cross this air-filled gap to gain asses to the diuron in the sand. Results Results showed that the three-member consortium with Variovorax sp. SRS16, A. globiformis D47 and Mortierella sp. LEJ702 achieved the fastest mineralisation of 14 C-labelled diuron measured as evolved 14 CO 2 (Figure 1). In addition, production of diuron metabolites by this consortium was minimal. Analyses of 16S rDNA suggested that the bacteria were transported more efficiently by LEJ702 than by LEJ703. Finally, it was found that the fungal growth differed for LEJ702 and LEJ703 in the three-member consortium. This study demonstrates new possibilities using efficient fungal-bacterial consortia for bioremediation of pesticide polluted soils.