Multipathway of Nitrogen Metabolism Revealed by Genome-Centered Metatranscriptomics from Pyrite-Guided Mixotrophic Partial Denitrification/Anammox Installations

Magnetite-mediated shifts in denitrifying consortia in bioelectrochemical system: Insights into species selection and metabolic dynamics

Conductive materials, such as magnetite, are recognized for their ability to enhance electron transfer and stimulate microbial metabolic activities. This study aimed to elucidate the metabolic potential and species interactions of dominant microbial species within complex communities influenced by magnetite. It indicated that the optimal dosage of magnetite at 4.5 mg/cm², would significantly improve denitrification efficiency and then reduce the time for removing 50 mg/L nitrate by 24.33 %. This enhancement was attributed to the reduced charge transfer resistance and the promoted formation of extracellular polymeric substances (EPS) facilitated by magnetite. Metagenomic analysis revealed that magnetite addition mitigated the competition among truncated denitrifiers for downstream nitrogen species, diminished the contribution of bacteria with complete nitrogen metabolism pathways to denitrification, and fostered a transition towards co-denitrification through interspecies cooperation, consequently leading to decreased nitrite accumulation and increased tolerance to nitrate shock loads. Furthermore, an in-depth study on a key species, Geobacter anodireducens JN93 within the bioelectrochemical system revealed that while magnetite with varying Fe(II) and Fe(III) ratios improved denitrification performance, the metabolic potential of Geobacter sp. varied for different nitrogen metabolism pathways. Collectively, this research provides insights into the microecological effects of magnetite on denitrifying consortia by shifting interspecific interactions via enhanced electron transfer.

External redox couple enhanced anammox sludge activity at low temperature: Insight into intracellular resource synthesis

Anaerobic ammonium oxidation (anammox), an energy-efficient deamination biotechnology, faces operational challenges in low-temperature environments. Enhancing the metabolic activity of anammox bacteria (AnAOB) is pivotal for advancing its application in mainstream municipal wastewater treatment. Inspired by the metabolic adaptability of AnAOB and based on our previous findings, this work investigated the enhancement of intracellular ATP and NADH synthesis through the exogenous supply of reduced humic acid (HAred) and H2O2 redox couple, aiming to augment AnAOB activity under low-temperature conditions. Our experimental setup involved continuous dosing of 0.0067 μmol g-1 volatile suspended solid of H2O2 and 10 mg g-1 volatile suspended solid of HAred into a mainstream anammox reactor operated at 15 °C with an influent TN content of 60 mg/L. The results showed that HAred / H2O2 couple succeeded in maintaining the effluent TN at 10.72 ± 0.91 mg l-1. The specific anammox activity, ATP and NADH synthesis levels of sludge increased by 1.34, 2.33 and 6.50 folds, respectively, over the control setup devoid of the redox couple. High-throughput sequencing analysis revealed that the relative abundance of Candidatus Kuenenia after adding HAred / H2O2 couple reached 3.65 % at the end of operation, which was 5.14 folds higher than that of the control group. Further metabolomics analysis underscored an activation in the metabolism of amino acids, nucleotides, and phospholipids, which collectively enhanced the availability of ATP and NADH for the respiratory processes. These findings may provide guidance on strategy development for improving the electron transfer efficiency of AnAOB and underscore the potential of using redox couples to promote the mainstream application of anammox technology.

Sulfur-carbon loop enhanced efficient nitrogen removal mechanism from iron sulfide-mediated mixotrophic partial denitrification/anammox systems

This study successfully established Iron Sulfide-Mediated mixotrophic Partial Denitrification/Anammox system, achieving nitrogen and phosphorus removal efficiency of 97.26% and 78.12%, respectively, with COD/NO3--N of 1.00. Isotopic experiments and X-ray Photoelectron Spectroscopy analysis confirmed that iron sulfide enhanced autotrophic Partial Denitrification performance. Meanwhile, various sulfur valence states functioned as electron buffers, reinforcing nitrogen and sulfur cycles. Microbial community analysis indicated reduced heterotrophic denitrifiers (OLB8, OLB13) under lower COD/NO3--N, creating more niche space for autotrophic bacteria and other heterotrophic denitrifiers. The prediction of functional genes illustrated that iron Sulfide upregulated genes related to carbon metabolism, denitrification, anammox and sulfur oxidation-reduction, facilitating the establishment of carbon-nitrogen-sulfur cycle. Furthermore, this cycle primarily produced electrons via nicotinamide adenine dinucleotide and sulfur oxidation-reduction processes, subsequently utilized within the electron transfer chain. In summary, the Partial Denitrification/Anammox system under the influence of iron sulfide achieved effient nitrogen removal by expediting electron transfer through the carbon-nitrogen-sulfur cycle.

Interspecies cooperation-driven photogenerated electron transfer processes and efficient multi-pathway nitrogen removal in the g-C3N4-anammox consortia biohybrid system

Photocatalytic materials-microbial biohybrid systems pave the way for solar-driven wastewater nitrogen removal. In this study, interspecies cooperation in photogenerated electron transfer and efficient nitrogen removal mechanism in the g-C3N4-anammox consortia biohybrid system were first deciphered. The results indicated that the essential extracellular electron carriers (cytochrome c and flavin) for anammox genomes were provided by associated bacteria (BACT3 and CHLO2). This cooperation, regulated by the ArcAB system and electron transfer flavoprotein, made anammox bacteria the primary photogenerated electron sink. Furthermore, an efficient photogenerated electron harness was used to construct a reductive glycine pathway (rGlyP) in anammox bacteria inventively, which coexisted with the Wood-Ljungdahl pathway (WLP), constituting a dual-pathway carbon fixation model, rGlyP-WLP. Carbon fixation products efficiently contributed to the tricarboxylic acid cycle, while inhibiting electron diversion in anabolism. Photogenerated electrons were targeted channeled into nitrogen metabolism-available electron carriers, enhancing anammox and dissimilatory nitrate reduction to ammonium (DNRA) processes. Moreover, ammonia assimilation by the glycine cleavage system in rGlyP established an alternative ammonia removal route. Ultimately, multi-pathway nitrogen removal involving anammox, DNRA, and rGlyP achieved 100 % ammonia removal and 94.25 % total nitrogen removal efficiency. This study has expanded understanding of anammox metabolic diversity, enhancing its potential application in carbon-neutral wastewater treatment.

NH2-MIL-101(Fe)-mediated photo-Fenton reaction enhanced simultaneous removal of nitrogen and refractory organics in anammox process through interfacial electron transfer

In this study, H2O2 (0.1 ‰) and NH2-MIL-101(Fe)-driven (150 mg/L) photo-Fenton-coupled anammox were proposed to simultaneously improve the removal efficiency of nitrogen and humic acid. Long-term experiments showed that the total nitrogen removal efficiency was increased by the photo-Fenton reaction to 91.9 ± 1.5 % by altering the bioavailability of refractory organics. Correspondingly, the total organic carbon removal efficiency was significantly increased. Microbial community analyses indicated that Candidatus_Brocadia maintained high activity during photo-Fenton reaction and was the most abundant genus in the reactor. Dissimilatory nitrate reduction to ammonium process and denitrification process were enhanced, resulting in reduced NO3--N production. The establishment of electron transfer between microorganisms and NH2-MIL-101 (Fe) improved the charge separation efficiency of the quantum dots and increased the intracellular adenosine triphosphate content of anammox bacteria. These results indicated that photo-Fenton-anammox process promoted the removal of nitrogen and refractory organics in one reactor which had good economic value and application prospects.