title: Aerobic Toluene Degraders in the Rhizosphere of a Constructed Wetland Model Show Diurnal Polyhydroxyalkanoate Metabolism.
abstract: Constructed wetlands (CWs) are successfully applied for the treatment of waters contaminated with aromatic compounds. In these systems, plants provide oxygen and root exudates to the rhizosphere and thereby stimulate microbial degradation processes. Root exudation of oxygen and organic compounds depends on photosynthetic activity and thus may show day-night fluctuations. While diurnal changes in CW effluent composition have been observed, information on respective fluctuations of bacterial activity are scarce. We investigated microbial processes in a CW model system treating toluene-contaminated water which showed diurnal oscillations of oxygen concentrations using metaproteomics. Quantitative real-time PCR was applied to assess diurnal expression patterns of genes involved in aerobic and anaerobic toluene degradation. We observed stable aerobic toluene turnover by Burkholderiales during the day and night. Polyhydroxyalkanoate synthesis was upregulated in these bacteria during the day, suggesting that they additionally feed on organic root exudates while reutilizing the stored carbon compounds during the night via the glyoxylate cycle. Although mRNA copies encoding the anaerobic enzyme benzylsuccinate synthase (bssA) were relatively abundant and increased slightly at night, the corresponding protein could not be detected in the CW model system. Our study provides insights into diurnal patterns of microbial processes occurring in the rhizosphere of an aquatic ecosystem.
  
  
  
  Constructed wetlands are a well-established and cost-efficient option for the bioremediation of contaminated waters. While it is commonly accepted knowledge that the function of CWs is determined by the interplay of plants and microorganisms, the detailed molecular processes are considered a black box. Here, we used a well-characterized CW model system treating toluene-contaminated water to investigate the microbial processes influenced by diurnal plant root exudation. Our results indicated stable aerobic toluene degradation by members of the Burkholderiales during the day and night. Polyhydroxyalkanoate synthesis in these bacteria was higher during the day, suggesting that they additionally fed on organic root exudates and reutilized the stored carbon compounds during the night. Our study illuminates microbial processes occurring in the rhizosphere of an aquatic ecosystem.
authors.affiliation: Helmholtz Centre for Environmental Research-UFZ, Department of Molecular Systems Biology, Leipzig, Germany.|Helmholtz Centre for Environmental Research-UFZ, Department of Environmental Biotechnology, Leipzig, Germany.
authors.forename: Vanessa
authors.initials: V
authors.lastname: Lünsmann
authors.affiliation: Helmholtz Centre for Environmental Research-UFZ, Department of Environmental Biotechnology, Leipzig, Germany.
authors.forename: Uwe
authors.initials: U
authors.lastname: Kappelmeyer
authors.affiliation: Helmholtz Centre for Environmental Research-UFZ, Department of Environmental Biotechnology, Leipzig, Germany.
authors.forename: Anja
authors.initials: A
authors.lastname: Taubert
authors.affiliation: Helmholtz Centre for Environmental Research-UFZ, Department of Isotope Biogeochemistry, Leipzig, Germany.
authors.forename: Ivonne
authors.initials: I
authors.lastname: Nijenhuis
authors.affiliation: Helmholtz Centre for Environmental Research-UFZ, Department of Molecular Systems Biology, Leipzig, Germany.|University of Leipzig, Faculty of Biosciences, Pharmacy and Psychology, Institute of Biochemistry, Leipzig, Germany.|Department of Biotechnology, Chemistry and Environmental Engineering, University of Aalborg, Aalborg, Denmark.
authors.forename: Martin
authors.initials: M
authors.lastname: von Bergen
authors.affiliation: Helmholtz Centre for Environmental Research-UFZ, Department of Environmental Biotechnology, Leipzig, Germany hermann.heipieper@ufz.de.
authors.forename: Hermann J
authors.initials: HJ
authors.lastname: Heipieper
authors.affiliation: Helmholtz Centre for Environmental Research-UFZ, Department of Environmental Biotechnology, Leipzig, Germany.
authors.forename: Jochen A
authors.initials: JA
authors.lastname: Müller
authors.affiliation: Helmholtz Centre for Environmental Research-UFZ, Department of Molecular Systems Biology, Leipzig, Germany.
authors.forename: Nico
authors.initials: N
authors.lastname: Jehmlich
mesh_terms: D000332:Aerobiosis; D020562:Betaproteobacteria / Q000378:metabolism*; D001711:Biotransformation; D002940:Circadian Rhythm; D020869:Gene Expression Profiling; D053858:Metabolic Networks and Pathways / Q000235:genetics; D010944:Plants; D054813:Polyhydroxyalkanoates / Q000378:metabolism*; D060888:Real-Time Polymerase Chain Reaction; D058441:Rhizosphere; D012988:Soil Microbiology; D014050:Toluene / Q000378:metabolism*; D014873:Water Pollutants / Q000378:metabolism; D053833:Wetlands
chemical_list: D054813:Polyhydroxyalkanoates; D014873:Water Pollutants; D014050:Toluene