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Interactions between ammonia-oxidising bacteria at the oxic/anoxic interface of natural ecosystems

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Dutch title: Interacties tussen ammonia-oxiderende bacteria op het oxische/anoxische grensvlak van natuurlijke ecosystemen
Reference no: OND1274375
Period: 1999 till 2001
Status: Completed

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  • Nederlandse Organisatie voor Wetenschappelijk Onderzoek; Aard- en Levenswetenschappen (NWO/ALW), more, sponsor

Problem definition: In the Scheldt estuary, at the zone where slainity and oxygen concentrations start to increase and ammonium concentrations concomitantly decrease, a chnge in dominant chemolithotrophic ammonia-oxidising bacteria is indicated by a shift in sequences of the 16S rDNA gene amplified from natural DNA. In the more freshwater part of the estuary a sequence type dominates that is mostly related to Nitrosomonas urea, whereas in the brakish part a sequence type dominated that is not closely related to one of the isolated Nitrosomonas species. The ecophysiological characteristics of the dominant tyes of ammonia-oxidising bacteria, which apparently lead to replacement of species within the community of ammonia-oxidising bacteria are not known. Objectives: The project aims at leucidating the ecophysiological characteistics of the dominant types of ammonia-oxidising bacteria that may play a selective role in theestablishement of the bacteria within the community. The dominant bacteria will be enriched and subsequently isolated in pure culture by means of continuous cultures under the conditions prevailing in the freshwater and the brakish part of the Scheldt estuary, respectively. The physiological characteristics of the enriched bacteria with respect to ammonium oxidation and oxygen consumption will be established. In addition, the resilence of the bacteria in relation to salt, oxygen and ammonium stress will be determined. Finally, the induction os specific enzymes related to an anaerobic metabolism will be determined during a change from oxic to anoxic conditions and vice versa. The latter will be done in close collaboration with microbiologists from the Universities of Delft and Amsterdam within the framework of a NWO programme Planning 2000: At the end of 1999 experiments in continuous and batch cultures were done to determine the inlfuence of salinity and oxygen partial pressure on the composition of the ammonia oxidiser community in the river Schelde. molecular analysis related to these experiments will be done in 2000. When oxygen appears out to be the controlling factor with respect to the observed shift in the dominant ammonia-oxidising bacteria, we will further enrich and isolate the enriched bacteria. Parallel to this, the competitive abilities of the enrichments at different oxygen, salt and ammonia concentrations will be investigated together with the ammonia and oxygen consumption kinetics. When oxygen is not the controlling factor for community consumtion along the saliniy gradient of the river Schelde, we wil searhc for other systems like roots or sediments, where oxigen is the factor, which causes population shifts of ammonia-oxidising bacteria. In addition the competitive abilities and the ammonia oxigen consumption kinetics of those enrichments, which were enriched at low amonia concentrations will be determined

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