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Samenstelling en functioneren van ijzerreducerende gemeenschappen in twee contrasterende omgevingen, n.l. vuilstort percolaat-vervuilde aquifer en estuarium sedimenten = Composition and functioning of iron-reducing communities in two contrasting environments, i.e. a landfill leachate-polluted aquifer and estuarine sediments
Lin, B. (2006). Samenstelling en functioneren van ijzerreducerende gemeenschappen in twee contrasterende omgevingen, n.l. vuilstort percolaat-vervuilde aquifer en estuarium sedimenten = Composition and functioning of iron-reducing communities in two contrasting environments, i.e. a landfill leachate-polluted aquifer and estuarine sediments. PhD Thesis. Vrije Universiteit Amsterdam: Amsterdam. ISBN 90-9020438-5. 165 pp.

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Document type: Dissertation

Keywords
    Marine; Brackish water; Fresh water

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Abstract
    The research in this thesis is to advance the mechanistic understanding of the geochemical, environmental and ecophysiological factors control on the activity of Fe (III)-reducing microbial populations in two contrasting environments, an aquifer polluted by a neighbouring landfill, and the estuarine sediments. The combination of field-scale hydrochemical measurements and laboratory experiments [including culture-independent 16S rRNA-based denaturing gradient gel electrophoresis (DGGE) and sequence analyses, and physiological characterization) was applied. Relationships between microbial community structure and hydrochemistry (redox process and biodegradation) in a landfill leachate-polluted aquifer (Banisveld, The Netherlands) were observed. Denitrification dominates above the clean plume whereas iron reduction is beneath the clean plume. Degradation of organic contaminants occurred under iron-reducing conditions in the plume of pollution, where members of the iron-reducing family Geobacteraceae strongly contributed to microbial communities (25% of the total Bacteria count). Pollution appeared to have selected for specific species out of the pool of Geobacteraceae, which are highly abundant and diverse. The clustering of Geobacteraceae-specific DGGE profiles and the presence of an intense DGGE band corresponded to the part of the aquifer where organic matter was attenuated at relatively high rates, indicating that Geobacteraceae community structure related to biodegradation. Besides Geobacteraceae also other iron-reducers, belonging to the genera Anaeromyxobacter, Geothrix, Serratia, Rhodoferax, Clostridium and Desulfitobacterium, were found to be present. Physiological characterization of G. metallireducens in a habitat-resembling retentostat revealed it has the lowest maintenance energy demand ever reported. Such low maintenance energy requirement and the ability to readily use alternative electron acceptors provide additional explanations for the dominance of Geobacters in the subsurface. The maximum growth yield (0.05- 0.09 C-mol biomass per C-mol acetate) and iron-reducing capacity of G. metallireducens was comparable to that of Shewanella putrefaciens, with the highest initial iron reduction rate for citrate-chelated Fe (III) (i.e. 7x10-9 mmol cell-1 h-1), whilst the rates were 40 (ferrihydrite) and 1500 times (nanohematite) lower respectively. The Scheldt ecosystem has been influenced heavily by anthropogenic activities with complicated organic matter input. The potential of microbial iron reduction in freshwater Appels (Belgium) and brackish Waarde (The Netherlands), the Scheldt estuary, were investigated. In addition to acquiring the knowledge of the complex of the iron-reducing microbial population at both sites, iron-reducing Geobacter, Shewanella, Geothrix, Anaeromyxobacteria and Alkaliphilus spp. were encountered but were not dominant (<1% of the cell counts) in either site. Ralstonia and Clostridium spp. appear to be dominant iron reducers instead. The presence of diverse and abundant (4.6 x 106, 2.4 x 105 cells g-1 sediment for Appels and Waarde, respectively) iron reducers, their versatility with respect to pH and temperature, their apparent ability to use alternative electron acceptors and donors, and substantial Fe (III) bioavailability strongly indicate a considerable potential for microbial iron reduction. On the basis of results in this thesis, the issues concerning (i) the important role of Geobacters in the biodegradation of aromatic compounds under iron-reducing conditions, (ii) composition of iron-reducing communities relative to environmental settings, and (iii) iron reduction as one of the active aspects of ecosystem functioning, are discussed.

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