Ammonia- and nitrite-oxidizing prokaryotes in lakes

Nitrification is a central process in the nitrogen cycle that microbially converts ammonia via nitrite to nitrate. Traditionally, this process was thought to be catalyzed by two separate groups of bacteria, but recent advances have dramatically changed our perspective on the nitrification process and renewed the interest to study the ecology of nitrifiers in different habitats. Nitrification research is currently focused on engineered systems, and particularly waste water treatment plants are often used as model systems to study niche preferences and environmental adaptations of nitrifying microbes. Our understanding of the nitrification processes in natural ecosystems, specifically in lakes, is incomplete. This project is breaking new ground as it will investigate the spatial and seasonal niche differentiation of co-occurring nitrifying communities in four different stratified lakes. We expect not only to learn if and how niche specialization and the co-occurrence of the nitrifying communities is determined by vertical variations of limnological parameters in lakes; we envisage that the project will yield critical data to understand on how (inter)seasonal fluctuation will affect the distribution of different lineages of ammonia- and nitrite-oxidizing microorganisms. Differentiation among groups of nitrifiers and species-specific adaptations will prove crucial in understanding how community succession affects the nitrification process. Another important outcome is that data produced within the project will provide significant insights in the microscale patchiness of nitrifying communities. The project will significantly enhance our understanding if the colonization of particulate material provides significant benefits, resulting in more stable communities within particle-attached populations than established by free living representatives. Although the project has no specific applied research orientation or water management outcomes, many changes predicted to accompany global warming, such as increasing lake water temperatures and hypolimnetic hypoxia will also highly impact microbial communities and related processes. Therefore, based on a better understanding of how lake warming influences physical and chemical lake dynamics and ultimately also affects nitrifying communities, the proposed research will have implications beyond the field of basic research in microbial ecology.