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Microbial key players in the oxidation of ammonium under oxygen limitation
Project leader: Prof. dr. ir. M. S. M. Jetten
Researcher(s): Dr. S. C. M. Haaijer
Starting date: 01-04-2010

Abstract
Nitrogen is one of the key nutrients in marine waters that may limit primary productivity. In this part of the programme we want to study ammonium oxidation under limiting oxygen conditions that mimic the oxygendepleted zones of the oceans. The importance of marine crenarchaea, versus bacterial ammonium oxidizers in marine nitrification will be investigated under controlled oxygen-limited conditions in the laboratory with cultures obtained through a previous joint DARWIN project. Field studies will be undertaken in the coastal and open ocean ecosystems to examine the biodiversity and relative importance of archaeal versus bacterial nitrification at low oxygen concentrations and to assess which microbes interact in the marine nitrogen cycle using state of the art techniques. The genomes of the relevant organisms have been sequenced, and are thus available to facilitate the study of the physiology and interactions on a molecular level in defined cocultures under oxygen limitation. Preliminary studies already showed that at least four groups of N-cycle microbes can co-exist under oxygen limitation. The results of this research will lead to significant new insights into the microbial roots of the global marine nitrogen cycle, and their adaptation to low oxygen concentrations.

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