Research Line 1
- Determining nitrous oxide and methane emission from the nitrogen removal stage of a municipal wastewater treatment plant (wwtp), and its metagenome sequencing
Nitrogen removal at the studied wwtp (Seehausen, Germany) consists of two steps. Nitrate reduction to dinitrogen gas occurs in the anaerobic chamber. Then wasterwater is led into the aerobic chamber where ammonium oxidation to nitrate occurs. The highest nitrous oxide (N2O) emission was measured in the aerobic nitrification zone suggesting that in this wwtp, aerobic ammonia-oxidizing bacteria were responsible for N2O production (project 1.1). The highest methane concentration was measured in the anaerobic denitrification zone (project 1.1). The metagenome of the wwtp revealed a diversity of microorganisms that could carry out the complete or different parts of the denitrification process, whereas the diversity of ammonia- and nitrite-oxidizing bacteria were lower (project 1.2 & 1.3). These results are not published yet.
Research Line 2
- Detailed description of nitrite and nitrate dependent anaerobic methane-oxidizing microorganisms (project 2.1)
Growth rate, doubling time, methane and nitrite affinities of the nitrite-dependent methane-oxidizing bacterium M. lanthanidiphila was determined and published in Applied and Environmental Microbiology. The complexes involved in nitrite-dependent methane oxidation were identified in M. lanthanidiphila, including the putative nitric oxide dismutase enzyme and published in BBA-Bioenergetics. The physiology of nitrate-dependent methane-oxidizing archaea M. nitroreducens was determined and revealed that they reduce nitrate to ammonium via nitrite and do not produce the greenhouse gas (GHG) N2O. Surprisingly, we showed that this biomass coupled the anaerobic oxidation of methane to the reduction of Fe3+ and Mn4+. This unprecedented discovery furthered our understanding of anaerobic methane-oxidizing pathways. This was published in PNAS and gathered press attention, and was even included in popular German quiz show (Wer Weiß Denn Sowas) as a question.
Investigation of cocultures of anammox and nitrite- and nitrate-dependent anaerobic methane-oxidizing microorganisms (project 2.2)
The growth of anammox bacteria on nitric oxide and ammonium, a new growth mode, was discovered. Under these conditions anammox bacteria did not produce N2O. This was published in Nature Communications and attracted press interest in the project. A new nitrite reductase, unrelated to known nitrite reductases was discovered in anammox bacteria and published in JBC. Proteins related to this new nitrite reductase was also detected in databases indicating it is prevalent in natural and engineered ecosystems. The structure of nitrite oxidoreductase from anammox bacteria was revealed and characterized, which was published in Nature Microbiology and attracted press attention.
Stable cocultures of anammox and nitrite & nitrate dependent anaerobic methane-oxidizing microorganisms were achieved, and the results were published in Applied Microbiology and Biotechnology. The coculture could effectively remove ammonium and methane simultaneously as proposed.
Investigation into the effect of oxygen on the cocultures of anammox and nitrite- & nitrate-dependent anaerobic methane-oxidizing microorganisms (project 2.3)
Cocultures of anammox and nitrite & nitrate dependent anaerobic methane-oxidizing microorganisms were subjected to oxygen and growth of aerobic methane and ammonia oxidizers were achieved under O2 limitation. This reactor contained aerobic and anaerobic methane and ammonium oxidizers, and functioned under conditions relevant for wastewater treatment providing the proof of concept for the wastewater treatment plant suggested in the grant proposal. Physiological and molecular analyses showed that the combination of N-damo and anammox activity under the continuous supply of limiting oxygen concentrations is feasible and can be implemented for the removal of methane and ammonium from wastewater. These results were published in Applied and Environmental Microbiology. A new protein (mHAO) capable of oxidation of hydroxylamine to NO, active up to at least 80 °C was purified from an aerobic methane oxidizer This novel protein mHAO enables methanotrophs to cope with high ammonia concentrations, leading to reduced methane emissions. However, this activity simultaneously contributes to ammonia loss and nitrite production, and potentially leads to N2O emissions. This was published in PNAS and attracted press attention.
The GREENT team also contributed an invited review to Current Opinion in Biotechnology covering the state-of-the-art and the future of ammonium and GHG removal from wastewater, covering all aspects of the GREENT project.
