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Nitrogen Cycle Bacteria in Agricultural Soils
Published in Vivek Kumar, Rhizomicrobiome Dynamics in Bioremediation, 2021
Guillermo Bravo, Paulina Vega-Celedón, Constanza Macaya, Ingrid-Nicole Vasconez, Michael Seeger
Nitrification Nitrification is an essential process in the nitrogen cycle in soils, which involves the biological oxidation of ammonia via nitrite to nitrate in the presence of oxygen by bacteria and archaea (Hernández et al. 2011). Several enzymes participate in the oxidation of reduced nitrogen compounds. The transmembrane enzyme ammonia monooxygenase oxidizes ammonia to hydroxylamine. NH2OH is subsequently oxidized by hydroxylamine oxidoreductase to nitrite (Hernández et al. 2011). Due to the high solubility of nitrate in agricultural systems, nitrification may cause negative effects, generating losses in crop production, and causing water eutrophication. It has been estimated that nitrification produces worldwide losses of 37 Tg of N year–1 in soil (Mosier et al. 2004).
Fundamentals and Modeling Aspects of Bioventing
Published in Subhas K. Sikdar, Robert L. Irvine, Fundamentals and Applications, 2017
C. M. Tellez, A. Aguilar-Aguila, R. G. Arnold, R. Z. Guzman
There are five genera in this group: Nitrosomonas, Nitrosococcus, Nitrospira, Nitrosolobus, and Nitrosovibrio. The best studied species of ammonia oxidizers is Nitrosomonas europaea, an obligate chemolitho-troph that initiates nitrification by the reductant-dependent oxidation of ammonia to hydroxylamine using ammonia monooxygenase (AMO). Reductant for AMO-catalyzed reactions is provided by the further oxidation of hydroxylamine to nitrite by hydroxylamine oxidoreductase (Figure 6). There is evidence that the AMO of N. europaea can also initiate cometabolic transformation of hydrocarbons (Hyman and Wood, 1983; 1984) and haloaliphatic compounds, including TCE (Arciero et al., 1989; Vanelli et al., 1990). The situation is entirely parallel to that of the methanotrophs in that halogenated substrates are transformed by both AMO and MMO without any direct metabolic benefit. Both enzymes consume reductant in the process, which must be replenished by metabolic activities at some expense to the organisms. For this reason, a primary or energy-yielding substrate is necessary for sustained cometabolic activity.
Recent advances in membrane aerated biofilm reactors
Published in Critical Reviews in Environmental Science and Technology, 2021
Duowei Lu, Hao Bai, Fangong Kong, Steven N. Liss, Baoqiang Liao
Based on current knowledge, oxygen consumption in biofilms is reflected by the formation of NO and N2O via AOB (Ma, Piscedda, & Smets, 2017). First, hydroxylamine oxidoreductase converts hydroxylamine (NH2OH) into nitrite and releases small amounts of NO and N2O. Second, the activity of nitrifier-encoded nitrite reductase and nitric oxide reductase reduce nitrite to NO and N2O in a process known as nitrifier denitrification. Both the DO and pH values affect the growth rates of AOB and NOB. The DO limitation impact is evaluated by O2 affinity constants. The effect of pH is two fold: (1) pH − enzyme effect: pH could directly impact AOB activity by increasing the demand for maintenance energy or changing the enzyme reaction mechanism, (2) substrate-speciation effect: local pH level determined free nitrous acid (FNA)/free ammonia (FA) speciation from the total NH4+/NO2− (Ma, Piscedda, & Smets, 2017).