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Abstract:

Natural dissolved organic matter (DOM) is the main source of carbon, energy and nutrients for heterotrophic microbial communities. DOM quality and quantity influences enzymatic activity, growth and composition of these communities. Research on DOM affecting specific functionality such as pesticide degradation is scarce. We examined in which way degradation activity of a triple-species microbial biofilm, synergistically mineralizing the phenylurea herbicide linuron, is affected when biofilms were grown on DOM formulations of natural origin with varying biodegradability prior to being exposed to linuron. Does synergism occur for natural organic compounds in multispecies biofilms and does this ameliorate biodegradation of xenobiotics requiring synergism? The linuron degrading consortium consists of Variovorax sp. WDL1 transforming linuron to 3,4-dichloroaniline (3,4-DCA) and N,O-dimethylhydroxylamine (N,O-DMHA). WDL1 uses 3,4-DCA as C-source but inefficiently and its excretion supports growth of Comamonas testosteroni WDL7. Hyphomicrobium sulfonivorans WDL6 grows on N,O-DMHA. Metabolic fingerprints were made of each consortium member separately and combined by two and three. Apart from niche complementarity, the consortium oxidized 20% more carbon sources of those tested which were not used by strains when assessed individually. This occurred due to a synergistic cooperation between WDL1 and WDL7 making more carbon sources accessible. Furthermore, biodegradability tests of eight DOM formulations of varying aromaticity inoculated with the consortium and its individual members indicated that the consortium acquired higher biodegradation for more recalcitrant formulations compared to individually assessed strains. This suggests that also for complex, uncharacterized DOM, synergistic cooperation between the three strains exists for moderate degradable compounds in low quality DOM. Triple-species biofilm development according to the applied DOM quality and its subsequent behavior towards linuron degradation was studied. The consortium was grown on different DOM formulations and after 20 days mature biofilms were fed with linuron as sole carbon and energy source. Biofilms cultivated in continuously fed flow chambers were visualized with CLSM by strain specific fluorescent labelling. Biofilm structure and composition correlated with DOM biodegradability. DOM fed biofilms often showed close spatial proximity of WDL1 and WDL7 which coincided with immediate removal of linuron afterwards. When separate structures of individual strains were formed a long lag phase in linuron removal occurred. We conclude that synergistic interactions occur between consortium members during the metabolism of natural organic compounds and their complex mixtures. DOM fed biofilms show distinct structural and compositional changes accordingly. When strain co-localization is enhanced, the synergistic interaction for linuron degradation is enhanced.