Aerobic methanotrophic bacterial communities in sediments of Lake Constance


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RAHALKAR, Monali, 2006. Aerobic methanotrophic bacterial communities in sediments of Lake Constance

@phdthesis{Rahalkar2006Aerob-8472, title={Aerobic methanotrophic bacterial communities in sediments of Lake Constance}, year={2006}, author={Rahalkar, Monali}, address={Konstanz}, school={Universität Konstanz} }

Rahalkar, Monali 2006 Rahalkar, Monali 2011-03-24T17:43:56Z Aerobic methanotrophic bacterial communities from sediments of Lake Constance were studied using cultivation and molecular approaches.<br /><br />Bacteria were cultivated by a gradient cultivation technique i.e. in opposing gradients of methane and oxygen. Growth of methanotrophs occurred as sharp bands where both methane and oxygen were consumed. Two types of bands were found, either close to the air exposed-end (top bands) or towards the methane exposed end (bottom bands). The methane flux was more to the bottom bands compared to the top bands while oxygen flux was almost the same to both the bands. The top bands consisted of Methylomonas sp. which were not the dominant members of the bacterial community, while the bottom band was dominated by Methylobacter sp. A sMMO containing Methylomonas sp. (strain LC 1) and a novel strain LC 2 were isolated from gradient cultures.<br /><br />Strain LC 2 was 94 % similar to Methylobacter tundripaludum, and based on its unique characters was classified as a new genus and species, Methylosoma difficile. Strain LC 2 grows on methane and methanol, GC content is 49.9%, main fatty acid is 16:1 ω7c and fixes nitrogen under micro-aerophilic conditions. This strain was further used to study the effects of high and low oxygen tension on growth as it showed accumulation of formaldehyde in the gas phase.<br /><br />Electron microscopy revealed that cells grown under low oxygen tension (LO) showed less intracytoplasmic membranes (ICM) and larger polyhydroxyalkanoates (PHA) granules compared to the cells grown under high oxygen tension (HO). LO showed higher oxygen uptake rates for toxic intermediates of methane oxidation like methanol and formaldehyde. High amounts of extracellular polymeric substances (EPS) were produced in HO cells, especially when grown in nitrogen depleted media. EPS could act as a diffusion barrier for oxygen and therefore would allow nitrogen fixation as well as protect the cells from effects like formaldehyde accumulation.<br />Clone library approach was used to study the methanotrophic communities from the littoral and profundal sediments. Clone libraries were constructed using the pmoA gene and 16S rDNA specific primers for Type I and Type II MOB using the DNA extracts from littoral and profundal sediment. A clear dominance of Type I MOB particularly Methylobacter related sequences was seen in both sediments. Although pmoA clone library from the profundal sediment showed dominance of a group of clones which were not related to cultured methanotrophs.<br /><br />A good correlation in the distribution profiles of methane and oxygen and the methanotroph numbers was observed in the littoral and profundal sediments of Lake Constance. Aerobic methane oxidation occurred in the top 1.5-2 cm of the littoral sediment, where highest copy numbers of pmoA genes (1-6 x 107 per g fresh weight sediment) were observed. In the profundal sediment, the methane and oxygen profiles indicated a zone of aerobic methane oxidation followed by a lower zone of anaerobic consumption. Highest copy numbers of pmoA genes (3.4 x 107 cells per g fresh weight)) were present in the 0.5-1.5 cm layer in the profundal sediment where peak aerobic methane oxidation took place. The consumption of methane in the anoxic zone could be attributed to either bioturbation activities or anaerobic oxidation of methane. According to a clone library approach, classical anaerobic methanotrophic archaea (ANME) were not detected in the 2-4 cm section of the profundal sediment.<br /> Aerobe methanotrophe Bakteriengemeinschaften im Sediment des Bodensees eng Aerobic methanotrophic bacterial communities in sediments of Lake Constance 2011-03-24T17:43:56Z application/pdf deposit-license

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