Diatoms - widespread nitrate respirers with overlooked impact on the marine nitrogen cycle

• Applicant: Dr. Anja Kamp
• Subject Area: Microbial Ecology and Applied Microbiology
• Term: from 2013 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 233025626

The proposed research project aims at revealing the eco physiological role and the environmental significance of nitrate storage and anaerobic nitrate respiration by diatoms, the most abundant eukaryotic phototrophs in the world's oceans. The paradigm that only prokaryotes but not eukaryotes are capable of dissimilatory nitrate reduction for energy generation is currently questioned. Nitrate respiration has already been shown to occur in marine foraminifers, a ciliate, and two fungal species. Only recently, a benthic, nitrate-storing diatom species was proven to use nitrate respiration as a mechanism to survive dark and anoxic conditions in the sediment for extended periods of time (Kamp et al. 2011, PNAS). It is unclear whether this species represents an isolated case or the tip of the iceberg. The main objectives of this research project are therefore (A) to screen for other diatoms that respire nitrate in hypoxic or anoxic marine ecosystems, (B) to identify the functional genes involved in eukaryotic nitrate respiration for use as molecular markers for cultivation-independent detection of nitrate-respiring diatoms in environmental samples, and (C) to evaluate the impact of this so far overlooked scenario on the marine nitrogen cycle, in particular in coastal sediments, during algal blooms, and when diatoms interact with prokaryotes in suspended aggregates. Eco-physiological experiments (e.g. 15N-labelling experiments, microsensor measurements) will be combined with modern molecular approaches (e.g. transcriptomics, functional-gene-based analyses) to arrive at a comprehensive understanding of anaerobic nitrate respiration by diatoms which may be the unrivaled nitrate-storing and nitrate-respiring eukaryotic photothrophs in the currently spreading anoxic and hypoxic zones of our oceans.

• DFG Programme: Research Grants