title: Pathways and key intermediates required for obligate aerobic ammonia-dependent chemolithotrophy in bacteria and Thaumarchaeota.
abstract: Chemolithotrophic ammonia-oxidizing bacteria and Thaumarchaeota are central players in the global nitrogen cycle. Obligate ammonia chemolithotrophy has been characterized for bacteria; however, large gaps remain in the Thaumarchaeotal pathway. Using batch growth experiments and instantaneous microrespirometry measurements of resting biomass, we show that the terrestrial Thaumarchaeon Nitrososphaera viennensis EN76(T) exhibits tight control over production and consumption of nitric oxide (NO) during ammonia catabolism, unlike the ammonia-oxidizing bacterium Nitrosospira multiformis ATCC 25196(T). In particular, pulses of hydroxylamine into a microelectrode chamber as the sole substrate for N. viennensis resulted in iterative production and consumption of NO followed by conversion of hydroxylamine to nitrite. In support of these observations, oxidation of ammonia in growing cultures of N. viennensis, but not of N. multiformis, was inhibited by the NO-scavenger PTIO. When based on the marginal nitrous oxide (N2O) levels detected in cell-free media controls, the higher levels produced by N. multiformis were explained by enzyme activity, whereas N2O in N. viennensis cultures was attributed to abiotic reactions of released N-oxide intermediates with media components. Our results are conceptualized in a pathway for ammonia-dependent chemolithotrophy in Thaumarchaea, which identifies NO as an essential intermediate in the pathway and implements known biochemistry to be executed by a proposed but still elusive copper enzyme. Taken together, this work identifies differences in ammonia-dependent chemolithotrophy between bacteria and the Thaumarchaeota, advances a central catabolic role of NO only in the Thaumarchaeotal pathway and reveals stark differences in how the two microbial cohorts contribute to N2O emissions.
authors.affiliation: Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada.
authors.forename: Jessica A
authors.initials: JA
authors.lastname: Kozlowski
authors.affiliation: Department of Ecogenomics and Systems Biology, Division Archaea Biology and Ecogenomics, University of Vienna, Wien, Austria.|Department of Biology I, Ludwig-Maximilians-University of Munich, Biocenter, Planegg-Martinsried, Germany.
authors.forename: Michaela
authors.initials: M
authors.lastname: Stieglmeier
authors.affiliation: Department of Ecogenomics and Systems Biology, Division Archaea Biology and Ecogenomics, University of Vienna, Wien, Austria.
authors.forename: Christa
authors.initials: C
authors.lastname: Schleper
authors.affiliation: Department of Biology, Queens College, The City University of New York, Flushing, NY, USA.|Institute of Marine Microbes & Ecospheres and State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen, China.
authors.forename: Martin G
authors.initials: MG
authors.lastname: Klotz
authors.affiliation: Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada.
authors.forename: Lisa Y
authors.initials: LY
authors.lastname: Stein
mesh_terms: D000641:Ammonia / Q000378:metabolism*; D001105:Archaea / Q000378:metabolism*; D001419:Bacteria / Q000378:metabolism*; D052837:Chemoautotrophic Growth; D019811:Hydroxylamine / Q000378:metabolism; D053858:Metabolic Networks and Pathways; D009573:Nitrites / Q000378:metabolism; D009609:Nitrous Oxide / Q000378:metabolism*; D010084:Oxidation-Reduction
chemical_list: D009573:Nitrites; D019811:Hydroxylamine; D000641:Ammonia; D009609:Nitrous Oxide