Mentor: Annette Bollmann, Ph.D.

Ammonia oxidizers perform the first and rate-limiting step of nitrification, which is a crucial process in the global nitrogen cycle. This process is carried out by ammonia-oxidizing bacteria (AOB), ammonia-oxidizing archaea (AOA), and complete ammonia oxidizers (comammox). In the ammonia oxidizer’s native environment, the different groups of ammonia oxidizers are often competing for limiting amounts of ammonium. The comammox strain Nitrospira sp. BO4 was able to outcompete the AOA Nitrosarchaeum sp. BO1 under limiting and excess ammonium (Ghimire-Kafle et al., 2024). However, this experiment was only conducted with one pair of strains under optimal growth conditions. Therefore, we conducted two additional experiments to investigate (1) the impact of starvation as environmental stressor on the outcome of the competition between Nitrospira sp. BO4 and Nitrosarchaeum sp. BO1 and (2) the competition between additional AOA and comammox strains.

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