title: Contrasting effects of singlet oxygen and hydrogen peroxide on bacterial community composition in a humic lake.
abstract: Light excitation of humic matter generates reactive oxygen species (ROS) in surface waters of aquatic ecosystems. Abundant ROS generated in humic matter rich lakes include singlet oxygen ((1)O2) and hydrogen peroxide (H2O2). Because these ROS differ in half-life time and toxicity, we compared their effects on microbial activity ((14)C-Leucine incorporation) and bacterial community composition (BCC) in surface waters of humic Lake Grosse Fuchskuhle (North-eastern Germany). For this purpose, experiments with water samples collected from the lake were conducted in July 2006, September 2008 and August 2009. Artificially increased (1)O2 and H2O2 concentrations inhibited microbial activity in water samples to a similar extent, but the effect of the respective ROS on BCC varied strongly. BCC analysis by 16S rRNA gene clone libraries and RT-PCR DGGE revealed ROS specific changes in relative abundance and activity of major bacterial groups and composition of dominating phylotypes. These changes were consistent in the three experiments performed in different years. The relative abundance of Polynucleobacter necessarius, Limnohabitans-related phylotypes (Betaproteobacteria), and Novosphingobium acidiphilum (Alphaproteobacteria) increased or was not affected by photo-sensitized (1)O2 exposure, but decreased after H2O2 exposure. The opposite pattern was found for Actinobacteria of the freshwater AcI-B cluster which were highly sensitive to (1)O2 but not to H2O2 exposure. Furthermore, group-specific RT-PCR DGGE analysis revealed that particle-attached P. necessarius and Limnohabitans-related phylotypes exhibit higher resistance to (1)O2 exposure compared to free-living populations. These results imply that (1)O2 acts as a factor in niche separation of closely affiliated Polynucleobacter and Limnohabitans-related phylotypes. Consequently, oxidative stress caused by photochemical ROS generation should be regarded as an environmental variable determining abundance, activity, and phylotype composition of environmentally relevant bacterial groups, in particular in illuminated and humic matter rich waters.
authors.affiliation: Institute for Microbiology and Molecular Biology, Justus-Liebig-University, Giessen, Germany; Institute for Applied Microbiology, Justus-Liebig-University, Giessen, Germany.
authors.forename: Stefanie P
authors.initials: SP
authors.lastname: Glaeser
authors.affiliation: Institute for Microbiology and Molecular Biology, Justus-Liebig-University, Giessen, Germany; Department of Cell & Molecular Biology, Uppsala University, Uppsala, Sweden.
authors.forename: Bork A
authors.initials: BA
authors.lastname: Berghoff
authors.affiliation: Institute for Microbiology and Molecular Biology, Justus-Liebig-University, Giessen, Germany.
authors.forename: Verena
authors.initials: V
authors.lastname: Stratmann
authors.affiliation: Leibniz Institute of Freshwater Ecology and Inland Fisheries, Stechlin, Germany; Institute for Biochemistry and Biology, Potsdam University, Potsdam, Germany.
authors.forename: Hans-Peter
authors.initials: HP
authors.lastname: Grossart
authors.affiliation: Institute for Microbiology and Molecular Biology, Justus-Liebig-University, Giessen, Germany.
authors.forename: Jens
authors.initials: J
authors.lastname: Glaeser
mesh_terms: D039903:Actinobacteria / Q000187:drug effects / Q000235:genetics / Q000254:growth & development; D020561:Alphaproteobacteria / Q000187:drug effects / Q000235:genetics / Q000254:growth & development; D001419:Bacteria / Q000145:classification / Q000187:drug effects / Q000235:genetics / Q000254:growth & development*; D020562:Betaproteobacteria / Q000187:drug effects / Q000235:genetics / Q000254:growth & development; D004269:DNA, Bacterial / Q000235:genetics; D058645:Denaturing Gradient Gel Electrophoresis; D017753:Ecosystem; D005618:Fresh Water / Q000737:chemistry* / Q000382:microbiology; D020563:Gammaproteobacteria / Q000187:drug effects / Q000235:genetics / Q000254:growth & development; D006812:Humic Substances / Q000032:analysis*; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D060106:Lakes; D016877:Oxidants / Q000494:pharmacology*; D010802:Phylogeny; D011157:Population Dynamics; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D026082:Singlet Oxygen / Q000494:pharmacology*; D014871:Water Microbiology
chemical_list: D004269:DNA, Bacterial; D006812:Humic Substances; D016877:Oxidants; D012336:RNA, Ribosomal, 16S; D026082:Singlet Oxygen; D006861:Hydrogen Peroxide