N-Control: Biological, ecological, and evolutionary controls on marine ammonia oxidation

• Applicant: Professor Dr. David Needham, Ph.D.
• Subject Area: Microbial Ecology and Applied Microbiology
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 528807633

Microorganisms dominate marine energy and biogeochemical cycles and account for about half of the primary productivity on earth. These communities turn over on the scale of days, thus the controls – biotic and abiotic -- on their biomass and activities are important to understand yet challenging to decipher since these organisms are extremely diverse and tiny. Nitrogen cycling, in particular nitrification whereby ammonia is converted to nitrite and then nitrate, is controlled by relatively few, yet diverse, lineages. The primary lineage responsible, ammonia oxidizing archaea (AOA), dominate biomass of the deep sea globally, fix 0.1-1 Pg Carbon per year, and produce nitrous oxide (N2O), a greenhouse gas ~300x more potent than carbon dioxide. Understanding the controls on these organisms and their ecosystem effects is, however, challenging to study due to the fact that their primary marine habitat is the global deep ocean. We found, through time-series observations, that AOA are also highly prevalent throughout the water column in the coastal southwest Baltic Sea during late fall and winter. Building upon this observation, this proposal, N-Control, will advance an understanding of how the underlying diversity and dynamics of AOA relate to their growth rates and ecosystem impacts, and how they are affected by environmental and biotic interactions. For work programme 1, we will perform genome sequencing of new AOA strains we have already enriched from the Baltic Sea (5), enrich and sequence additional ones. In parallel we will sequence bulk microbial communities from two Baltic Sea time-series sites, focusing on fall and winter months. The objective is to determine niche-defining gene sets and allele variability of this diverse group in the Baltic Sea, and how they relate to environmental parameters like nitrous oxide, ammonium, and temperature. For work programme 2, we will quantify field rates of ammonia oxidation, carbon fixation at one Baltic Sea time-series site, with the objective to understand the ecosystem impacts of the AOA. Additionally, for work programme 2, we will assess how parameters like temperature influence nitrous oxide production of AOA. Finally, for work programme 3, we will identify and quantify biotic controls on AOA. We will utilize full microbial community profiles and environmental data to predict co-occurrence patterns of microbes and develop a microbial community model for the organisms responsible for nitrification in the Baltic Sea. We will also test the prediction of AOA viruses from metagenomes, and quantify the impacts of protistan grazing and viral lysis on the growth rates. In conclusion, “N-Control”, will advance an understanding of the globally relevant AOA in a highly ecologically relevant, model ecosystem of the Baltic Sea which is experiencing rapid climate change and impacts from numerous other anthropogenic forces.

• DFG Programme: Research Grants