Publications (4)20.88 Total impact
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Article: Chemolithotrophic nitrate-dependent Fe(II)-oxidizing nature of actinobacterial subdivision lineage TM3.
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ABSTRACT: Anaerobic nitrate-dependent Fe(II) oxidation is widespread in various environments and is known to be performed by both heterotrophic and autotrophic microorganisms. Although Fe(II) oxidation is predominantly biological under acidic conditions, to date most of the studies on nitrate-dependent Fe(II) oxidation were from environments of circumneutral pH. The present study was conducted in Lake Grosse Fuchskuhle, a moderately acidic ecosystem receiving humic acids from an adjacent bog, with the objective of identifying, characterizing and enumerating the microorganisms responsible for this process. The incubations of sediment under chemolithotrophic nitrate-dependent Fe(II)-oxidizing conditions have shown the enrichment of TM3 group of uncultured Actinobacteria. A time-course experiment done on these Actinobacteria showed a consumption of Fe(II) and nitrate in accordance with the expected stoichiometry (1:0.2) required for nitrate-dependent Fe(II) oxidation. Quantifications done by most probable number showed the presence of 1 × 10(4) autotrophic and 1 × 10(7) heterotrophic nitrate-dependent Fe(II) oxidizers per gram fresh weight of sediment. The analysis of microbial community by 16S rRNA gene amplicon pyrosequencing showed that these actinobacterial sequences correspond to ∼0.6% of bacterial 16S rRNA gene sequences. Stable isotope probing using (13)CO2 was performed with the lake sediment and showed labeling of these Actinobacteria. This indicated that they might be important autotrophs in this environment. Although these Actinobacteria are not dominant members of the sediment microbial community, they could be of functional significance due to their contribution to the regeneration of Fe(III), which has a critical role as an electron acceptor for anaerobic microorganisms mineralizing sediment organic matter. To the best of our knowledge this is the first study to show the autotrophic nitrate-dependent Fe(II)-oxidizing nature of TM3 group of uncultured Actinobacteria.The ISME Journal 03/2013; · 7.38 Impact Factor -
Article: DNA-, rRNA- and mRNA-based stable isotope probing of aerobic methanotrophs in lake sediment.
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ABSTRACT: A stable isotope probing (SIP) approach was used to study aerobic methane-oxidizing bacteria (methanotrophs) in lake sediment. Oligotrophic Lake Stechlin was chosen because it has a permanently oxic sediment surface. 16S rRNA and the pmoA gene, which encodes a subunit of the methane monooxygenase enzyme, were analysed following the incubation of sediment with (13) CH(4) and the separation of (13) C-labelled DNA and RNA from unlabelled nucleic acids. The incubation with (13) CH(4) was performed over a 4-day time-course and the pmoA genes and transcripts became progressively labelled such that approximately 70% of the pmoA genes and 80% of the transcripts were labelled at 96 h. The labelling of pmoA mRNA was quicker than pmoA genes, demonstrating that mRNA-SIP is more sensitive than DNA-SIP; however, the general rate of pmoA transcript labelling was comparable to that of the pmoA genes, indicating that the incorporation of (13) C into ribonucleic acids of methanotrophs was a gradual process. Labelling of Betaproteobacteria was clearly seen in analyses of 16S rRNA by DNA-SIP and not by RNA-SIP, suggesting that cross-feeding of the (13) C was primarily detected by DNA-SIP. In general, we show that the combination of SIP approaches provided valuable information about the activity and growth of the methanotrophic populations and the cross-feeding of methanotroph metabolites by other microorganisms.Environmental Microbiology 01/2011; 13(5):1153-67. · 5.84 Impact Factor -
Article: Structure and topology of microbial communities in the major gut compartments of Melolontha melolontha larvae (Coleoptera: Scarabaeidae).
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ABSTRACT: Physicochemical gut conditions and the composition and topology of the intestinal microbiota in the major gut compartments of the root-feeding larva of the European cockchafer (Melolontha melolontha) were studied. Axial and radial profiles of pH, O2, H2, and redox potential were measured with microsensors. Terminal restriction fragment length polymorphism (T-RFLP) analysis of bacterial 16S rRNA genes in midgut samples of individual larvae revealed a simple but variable and probably nonspecific community structure. In contrast, the T-RFLP profiles of the hindgut samples were more diverse but highly similar, especially in the wall fraction, indicating the presence of a gut-specific community involved in digestion. While high acetate concentrations in the midgut and hindgut (34 and 15 mM) corroborated the presence of microbial fermentation in both compartments, methanogenesis was confined to the hindgut. Methanobrevibacter spp. were the only methanogens detected and were restricted to this compartment. Bacterial 16S rRNA gene clone libraries of the hindgut were dominated by clones related to the Clostridiales. Clones related to the Actinobacteria, Bacillales, Lactobacillales, and gamma-Proteobacteria were restricted to the lumen, whereas clones related to the beta- and delta-Proteobacteria were found only on the hindgut wall. Results of PCR-based analyses and fluorescence in situ hybridization of whole cells with group-specific oligonucleotide probes documented that Desulfovibrio-related bacteria comprise 10 to 15% of the bacterial community at the hindgut wall. The restriction of the sulfate-reducer-specific adenosine-5'-phosphosulfate reductase gene apsA to DNA extracts of the hindgut wall in larvae from four other populations in Europe suggested that sulfate reducers generally colonize this habitat.Applied and Environmental Microbiology 09/2005; 71(8):4556-66. · 3.83 Impact Factor -
Article: Stable-isotope probing of microorganisms thriving at thermodynamic limits: syntrophic propionate oxidation in flooded soil.
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ABSTRACT: Propionate is an important intermediate of the degradation of organic matter in many anoxic environments. In methanogenic environments, due to thermodynamic constraints, the oxidation of propionate requires syntrophic cooperation of propionate-fermenting proton-reducing bacteria and H(2)-consuming methanogens. We have identified here microorganisms that were active in syntrophic propionate oxidation in anoxic paddy soil by rRNA-based stable-isotope probing (SIP). After 7 weeks of incubation with [(13)C]propionate (<10 mM) and the oxidation of approximately 30 micromol of (13)C-labeled substrate per g dry weight of soil, we found that archaeal nucleic acids were (13)C labeled to a larger extent than those of the bacterial partners. Nevertheless, both terminal restriction fragment length polymorphism and cloning analyses revealed Syntrophobacter spp., Smithella spp., and the novel Pelotomaculum spp. to predominate in "heavy" (13)C-labeled bacterial rRNA, clearly showing that these were active in situ in syntrophic propionate oxidation. Among the Archaea, mostly Methanobacterium and Methanosarcina spp. and also members of the yet-uncultured "rice cluster I" lineage had incorporated substantial amounts of (13)C label, suggesting that these methanogens were directly involved in syntrophic associations and/or thriving on the [(13)C]acetate released by the syntrophs. With this first application of SIP in an anoxic soil environment, we were able to clearly demonstrate that even guilds of microorganisms growing under thermodynamic constraints, as well as phylogenetically diverse syntrophic associations, can be identified by using SIP. This approach holds great promise for determining the structure and function relationships of further syntrophic or other nutritional associations in natural environments and for defining metabolic functions of yet-uncultivated microorganisms.Applied and Environmental Microbiology 10/2004; 70(10):5778-86. · 3.83 Impact Factor
