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1. Evaluation of anammox biocathode in microbial desalination and wastewater treatment

   https://doi.org/https://doi.org/10.1016/j.cej.2018.02.088  

   Bahareh Kokabian, Veera Gnaneswar (June 2018, Chemical engineering journal)

   This study presents the use of an autotrophic microorganism, Anammox bacteria, as a sustainable biocatalyst/biocathode in microbial desalination cells (MDCs) for energy-positive wastewater treatment. We report the first proof of concept study to prove that anammox mechanism can be beneficial in MDCs to provide simultaneous removal of carbon and nitrogen compounds from wastewater while producing bioelectricity. A series of experiments were conducted to enrich and evaluate the anammox mechanism and the process performance in continuous, fed-batch mode conditions. Coulombic efficiency of MDCs and nitrite and ammonium removal of wastewater increased in successive batch studies. A maximum power density of 0.092 Wm−3 (or a maximum current density of 0.814 A m−3) with more than 90% of ammonium removal was achieved in this system. We calculated the Nernst potential for the nitrite reduction in the anammox biocathode chamber and compared with experimental values. Sequential removal of carbon and nitrogen compounds in anode and cathode chambers respectively, was also evaluated. Further, the inhibition effect of high nitrogen concentrations and the variations in microbial community profiles, especially, anammox presence was studied at different carbon and ammonia concentrations. Experimental studies and microbial community analysis are presented in detail. 

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2. Autotrophic and mixotrophic metabolism of an anammox bacterium revealed by in vivo 13C and 2H metabolic network mapping

   https://doi.org/10.1038/s41396-020-00805-w  

   Lawson, Christopher E.; Nuijten, Guylaine H.; de Graaf, Rob M.; Jacobson, Tyler B.; Pabst, Martin; Stevenson, David. M.; Jetten, Mike S.; Noguera, Daniel R.; McMahon, Katherine D.; Amador-Noguez, Daniel; et al (October 2020, The ISME Journal)

   null (Ed.)

   Abstract Anaerobic ammonium-oxidizing (anammox) bacteria mediate a key step in the biogeochemical nitrogen cycle and have been applied worldwide for the energy-efficient removal of nitrogen from wastewater. However, outside their core energy metabolism, little is known about the metabolic networks driving anammox bacterial anabolism and use of different carbon and energy substrates beyond genome-based predictions. Here, we experimentally resolved the central carbon metabolism of the anammox bacterium Candidatus ‘Kuenenia stuttgartiensis’ using time-series 13 C and 2 H isotope tracing, metabolomics, and isotopically nonstationary metabolic flux analysis. Our findings confirm predicted metabolic pathways used for CO 2 fixation, central metabolism, and amino acid biosynthesis in K. stuttgartiensis , and reveal several instances where genomic predictions are not supported by in vivo metabolic fluxes. This includes the use of the oxidative branch of an incomplete tricarboxylic acid cycle for alpha-ketoglutarate biosynthesis, despite the genome not having an annotated citrate synthase. We also demonstrate that K. stuttgartiensis is able to directly assimilate extracellular formate via the Wood–Ljungdahl pathway instead of oxidizing it completely to CO 2 followed by reassimilation. In contrast, our data suggest that K. stuttgartiensis is not capable of using acetate as a carbon or energy source in situ and that acetate oxidation occurred via the metabolic activity of a low-abundance microorganism in the bioreactor’s side population. Together, these findings provide a foundation for understanding the carbon metabolism of anammox bacteria at a systems-level and will inform future studies aimed at elucidating factors governing their function and niche differentiation in natural and engineered ecosystems. 

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3. “ Candidatus Subterrananammoxibiaceae,” a New Anammox Bacterial Family in Globally Distributed Marine and Terrestrial Subsurfaces

   https://doi.org/10.1128/aem.00800-23  

   Zhao, Rui; Le Moine Bauer, Sven; Babbin, Andrew R. (January 2023, Applied and Environmental Microbiology)

   Spear, John R. (Ed.)

   ABSTRACT Bacteria specialized in anaerobic ammonium oxidation (anammox) are widespread in many anoxic habitats and form an important functional guild in the global nitrogen cycle by consuming bio-available nitrogen for energy rather than biomass production. Due to their slow growth rates, cultivation-independent approaches have been used to decipher their diversity across environments. However, their full diversity has not been well recognized. Here, we report a new family of putative anammox bacteria, “ Candidatus Subterrananammoxibiaceae,” existing in the globally distributed terrestrial and marine subsurface (groundwater and sediments of estuary, deep-sea, and hadal trenches). We recovered a high-quality metagenome-assembled genome of this family, tentatively named “ Candidatus Subterrananammoxibius californiae,” from a California groundwater site. The “ Ca. Subterrananammoxibius californiae” genome not only contains genes for all essential components of anammox metabolism (e.g., hydrazine synthase, hydrazine oxidoreductase, nitrite reductase, and nitrite oxidoreductase) but also has the capacity for urea hydrolysis. In an Arctic ridge sediment core where redox zonation is well resolved, “ Ca. Subterrananammoxibiaceae” is confined within the nitrate-ammonium transition zone where the anammox rate maximum occurs, providing environmental proof of the anammox activity of this new family. Phylogenetic analysis of nitrite oxidoreductase suggests that a horizontal transfer facilitated the spreading of the nitrite oxidation capacity between anammox bacteria (in the Planctomycetota phylum) and nitrite-oxidizing bacteria from Nitrospirota and Nitrospinota . By recognizing this new anammox family, we propose that all lineages within the “ Ca. Brocadiales” order have anammox capacity. IMPORTANCE Microorganisms called anammox bacteria are efficient in removing bioavailable nitrogen from many natural and human-made environments. They exist in almost every anoxic habitat where both ammonium and nitrate/nitrite are present. However, only a few anammox bacteria have been cultured in laboratory settings, and their full phylogenetic diversity has not been recognized. Here, we present a new bacterial family whose members are present across both the terrestrial and marine subsurface. By reconstructing a high-quality genome from the groundwater environment, we demonstrate that this family has all critical enzymes of anammox metabolism and, notably, also urea utilization. This bacterium family in marine sediments is also preferably present in the niche where the anammox process occurs. These findings suggest that this novel family, named “ Candidatus Subterrananammoxibiaceae,” is an overlooked group of anammox bacteria, which should have impacts on nitrogen cycling in a range of environments. 

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4. Toxicity of azoles towards the anaerobic ammonium oxidation (anammox) process

   https://doi.org/10.1002/jctb.6285  

   Lakhey, Nivrutti; Li, Guangbin; Sierra‐Alvarez, Reyes; Field, Jim_A (December 2019, Journal of Chemical Technology & Biotechnology)

   Abstract BACKGROUNDAzoles are an important class of compounds that are widely used as corrosion inhibitors in aircraft de‐icing agents, cooling towers, semiconductor manufacturing and household dishwashing detergents. They also are important moieties in pharmaceutical drugs and fungicides. Azoles are widespread emerging contaminants occurring frequently in water bodies. Azole compounds can potentially cause inhibition towards key biological processes in natural ecosystems and wastewater treatment processes. Of particular concern is the inhibition of azoles to the nitrification process (aerobic oxidation of ammonium). This study investigated the acute toxicity of azole compounds towards the anaerobic ammonia oxidation (anammox) process, which is an important environmental biotechnology gaining traction for nutrient‐nitrogen removal during wastewater treatment. In this study, using batch bioassay techniques, the anammox toxicity of eight commonly occurring azole compounds was evaluated. RESULTSThe results show that 1H‐benzotriazole and 5‐methyl‐1H‐benzotriazole had the highest inhibitory effect on the anammox process, causing 50% decrease in anammox activity (IC₅₀) at concentrations of 19.6 and 17.8 mg L⁻¹, respectively. 1H‐imidazole caused less severe toxicity with an IC₅₀of 79.4 mg L⁻¹. The other azole compounds were either nontoxic (1H‐pyrazole, 1H‐1,2,4‐triazole and 1‐methyl‐pyrazole) or at best mildly toxic (1H‐benzotriazole‐5‐carboxylic acid and 3,5‐dimethyl‐1H‐pyrazole) towards the anammox bacteria at the concentrations tested. CONCLUSIONSThis study showed that most azole compounds tested displayed mild to low or no toxicity towards the anammox bacteria. The anammox bacteria were found to be far less sensitive to azoles compared to nitrifying bacteria. © 2019 Society of Chemical Industry 

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5. Microbial nitrogen loss by coupled nitrification to denitrification and anammox in a permeable subterranean estuary at Gloucester Point, Virginia

   https://doi.org/https://doi.org/10.1016/j.marpolbul.2021.112440  

   Wu, Jiapeng; Hong, Yiguo; Wilson, Stephanie J; Song, Bongkeun (July 2021, Marine pollution bulletin)

   null (Ed.)

   The nitrogen (N) loss processes have not been well examined in subterranean estuaries (STEs) between land and sea. We utilized a 15N isotope tracer method, q-PCR, and high-throughput sequencing to reveal the activities, abundances, and community compositions of N loss communities in a STE in Gloucester Point, Virginia, US. The highest activities, abundances and diversity of denitrifiers and anammox bacteria were detected at 50–60 cm depth in the aerobic-anaerobic transition zone (AATZ) characterized by sharp redox gradients. nirS-denitrifiers and anammox bacteria were affiliated to 10 different clusters and three genera, respectively. Denitrification and anammox played equal roles with an estimated N loss of 13.15 mmol N m−3 day−1. A positive correlation between ammonia oxidizing prokaryote abundances and DO as well as NOx− suggested that nitrification produces NOx− which supports the hotspot of denitrification and anammox within the AATZ. Overall, these results highlight the roles of N loss communities in STEs 

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