Bacillus velezensis M3-1 strain isolated from the sediment of Myriophyllum aquatium constructed wetlands was found to efficiently convert NO3--N to NO2--N, and the requirements for carbon source addition were not very rigorous. This work demonstrates, for the first time, the feasibility of using the synergy of anammox and Bacillus velezensis M3-1 microorganisms for nitrogen removal. In this study, the possibility of M3-1 that converted NO3--N produced by anammox to NO2--N was verified in an anaerobic reactor. The NO3--N reduction ability of M3-1 and denitrifying bacteria in coupling system was investigated under different C/N conditions, and it was found that M3-1 used carbon sources preferentially over denitrifying bacteria. By adjusting the ratio of NH4+-N to NO2--N, it was found that the NO2--N converted from NO3--N by M3-1 participated in the original anammox.The nitrogen removal efficacy (NRE) of the coupled system was increased by 12.1%, compared to the control group anammox system at C/N = 2:1. Functional gene indicated that it might be a nitrate reducing bacterium.This study shows that the nitrate reduction rate achieved by the Bacillus velezensis M3-1 can be high enough for removing nitrate produced by anammox process, which would enable improve nitrogen removal from wastewater.

Partial nitrification (PN) is crucial for anaerobic ammonium oxidation (ANAMMOX), but faces challenges such as high energy demands and process control. Recent research has highlighted additives like magnetite as potential alternatives to conventional electron acceptors (O₂ and NO₂-) for enhancing ammonium (NH4+) oxidation with lower energy consumption. This study investigated the effect of adding 50 mg/L of magnetite to ANAMMOX reactors, resulting in improved nitrogen (N) removal efficiency. The magnetite-added ANAMMOX (M-ANA) reactor yielded N removal efficiencies of 71 %, 66 %, and 57 % for NH4+:NO2- molar ratios of 1:1.3, 1:0.8, and 1:0.5, respectively. The M-ANA reactor operated under a 0.5 mol lower NO2- concentration achieved similar performance to the control ANAMMOX (C-ANA) reactor operated with a theoretical amount of NO2-. Moreover, the M-ANA reactor showed the potential to remove NH4+ by 56 % without any NO2- supplementation. Metagenomic analysis showed that the addition of magnetite significantly improved the relative abundance of microorganisms involved in the FEAMMOX reaction, such as Fimbriimonas ginsengisoli and Pseudomonas stutzeri. It also facilitated positive mutualism between ANAMMOX and FEAMMOX reactions. In addition, M-ANA granules exhibited a dense and compact structure compared with C-ANA, and the presence of magnetite facilitated the formation of resilient granules. Notably, the useful protein (Heme C) concentration and specific microbial activity in the M-ANA reactor were 1.3 and 2.2 times higher than those in the C-ANA reactor. Overall, the results demonstrate that an appropriate amount of magnetite can enhance the N removal efficiency while reducing the energy input requirements and associated carbon emissions. These findings can guide the future development of carbon- and energy-neutral N removal processes.

Sulfamethoxazole (SMX) is frequently detected in wastewater where anammox applications are promising. While it has been demonstrated that anammox consortia can adapt to SMX stress, the underlying community adaptation strategy has not yet been fully addressed. Therefore, in this study, we initially ascertained anammox consortia\'s ability to co-metabolize SMX in batch tests. Then, a 200-day domestication process of anammox consortia under SMX stress was carried out with community variations and transcriptional activities monitored by metagenomic and metatranscriptomic sequencing techniques. Despite the initial drop to 41.88 %, the nitrogen removal efficiency of the anammox consortia rebounded to 84.64 % post-domestication under 5 mg/L SMX. Meanwhile, a 4.85-fold accumulation of antibiotic resistance genes (ARGs) under SMX stress was observed as compared to the control group. Interestingly, the anammox consortia may unlock the SMX-inhibited folate synthesis pathway through a novel interspecies cooperation triangle among Nitrospira (NAA), Desulfobacillus denitrificans (DSS1), and the core anammox population Candidatus Brocadia sinica (AMX1), in which the modified dihydropteroate synthase (encoded by sul1) of NAA reconnected the symbiotic cooperation between AMX1 and DSS1. Overall, this study provides a new model for the adaptation strategies of anammox consortia to SMX stress.

The Mariana Trench (MT) is the deepest part of the ocean on Earth. Previous studies have described the microbial community structures and functional potential in the seawater and surface sediment of MT. Still, the metabolic features and adaptation strategies of the microorganisms involved in nitrogen cycling processes are poorly understood. In this study, comparative metagenomic approaches were used to study microbial nitrogen cycling in three MT habitats, including hadal seawater [9,600-10,500 m below sea level (mbsl)], surface sediments [0-46 cm below seafloor (cmbsf) at a water depth between 7,143 and 8,638 mbsl], and deep sediments (200-306 cmbsf at a water depth of 8,300 mbsl). We identified five new nitrite-oxidizing bacteria (NOB) lineages that had adapted to the oligotrophic MT slope sediment, via their CO2 fixation capability through the reductive tricarboxylic acid (rTCA) or Calvin-Benson-Bassham (CBB) cycle; an anammox bacterium might perform aerobic respiration and utilize sedimentary carbohydrates for energy generation because it contains genes encoding type A cytochrome c oxidase and complete glycolysis pathway. In seawater, abundant alkane-oxidizing Ketobacter species can fix inert N2 released from other denitrifying and/or anammox bacteria. This study further expands our understanding of microbial life in the largely unexplored deepest part of the ocean.
OBJECTIVE: The metabolic features and adaptation strategies of the nitrogen cycling microorganisms in the deepest part of the ocean are largely unknown. This study revealed that anammox bacteria might perform aerobic respiration in response to nutrient limitation or O2 fluctuations in the Mariana Trench sediments. Meanwhile, an abundant alkane-oxidizing Ketobacter species could fix N2 in hadal seawater. This study provides new insights into the roles of hadal microorganisms in global nitrogen biogeochemical cycles. It substantially expands our understanding of the microbial life in the largely unexplored deepest part of the ocean.

Anaerobic biological treatment technology, especially denitrification and anaerobic ammonia oxidation (anammox) technology as mainstream process, played dominant role in the field of biological wastewater treatment. However, the above process was prone to sludge floating during high load operation and thereby affecting the efficient and stable operation of the system. Excessive production of extracellular polymeric substance (EPS) was considered to be the main reason for anaerobic granular sludge flotation, but the summaries in this area were not comprehensive enough. In this review, the potential mechanisms of denitrification and anammox sludge floatation were discussed from the perspective of granular sludge structural characteristics, nutrient transfer, and microbial flora change respectively, and the corresponding control strategies were also summarized. Finally, this paper indicated that future research on sludge flotation should focus on reducing the negative effects of EPS in sludge particles.

The widespread use of surfactants raise challenges to biological wastewater treatment. Anaerobic ammonium oxidation (anammox) process has the potential to treat wastewater containing anionic surfactants, but the response of anammox consortia at the molecular level under long-term exposure is unclear. Using high-throughput sequencing and gene quantification, combined with molecular docking, the effect of sodium dodecyl sulfonate (SDS) on anammox consortia were investigated. Levels of reactive oxygen species (ROS) might be lower than the threshold of oxidative damage, while the increase of lactate dehydrogenase (LDH) represented the cell membrane damage. Decreased abundance of functional genes (hdh, hzsA and nirS) indicated the decrease of the anammox bacterial abundance. Trace amounts of N-acyl homoserine lactone (AHL, C6-HSL, C8-HSL and C12-HSL) contained in influent could induce endogenous quorum sensing (QS), which could regulate the correlation between functional bacteria to optimize the microbial community and strengthen the resistance of anammox consortia to SDS. In addition, the proliferation of disinfectant resistance genes might increase the environmental pathogenicity of sewage discharge. This work highlights the potential response mechanism of anammox consortium to surfactants and provides a universal microbial-friendly bioenhancement strategy based on QS.

This study constructed an integrated algae/partial nitrification/anammox biofilm system and operated it for 240 days. The total nitrogen removal efficiency exceeded 90 %. The structure, compositions, and function of this symbiotic biofilm, which played a pivotal role in the system, were analyzed in detail. Microscope photos and fluorescence in situ hybridization both showed that bacteria and algae were well integrated. The dissolved oxygen gradient further confirmed that different functional microorganisms grew at varying depths within biofilm. Algae formed an oxygen-producing zone (0-0.48 mm), followed by ammonia oxidizing bacteria (AOB) consuming oxygen to form an oxygen-consuming zone (0.48-0.86 mm), and anaerobic ammonia oxidizing bacteria (AnAOB) removed nitrogen in anaerobic zone (>0.86 mm). Chlorella, Nitrosomonas and Candidatus_Kuenenia were identified as the dominant algae, AOB and AnAOB, with relative abundances of 11.80 %, 19.77 % and 3.07 %, respectively. This layered biofilm benefitted providing a suitable environment for various microorganisms to survive within a complex biofilm.

The DEnitrifying AMmonium OXidation (DEAMOX) has been proven to be a promising process treating contaminated surface water containing ammonia and nitrate, while the enrichment of the slow-growing anammox bacteria (AnAOB) remains a challenge. In this study, a novel polyurethane-adhesion vermiculite/tourmaline (VTP) modified carrier was developed to achieve effective enrichment of AnAOB. The results demonstrated that the VTP-1 (vermiculite: tourmaline = 1:1) system exhibited the greatest performance with the total nitrogen removal efficiency reaching 87.6% and anammox contributing 63% to nitrogen removal. Scanning electron microscope analysis revealed the superior biofilm structure of the VTP-1 carrier, providing attachment for AnAOB. The addition of VTP-1 promoted the secretion of EPS (extracellular polymeric substances) by microorganisms, which increased to 85.34 mg/g VSS, contributing to the aggregation of anammox cells. The favorable substrate microenvironment created by NH4+ adsorption and NO2- supply via partial denitrification process facilitated the growth of AnAOB. The relative abundance of Candidatus Brocadia and Thauera increased from 0.04% to 0.3%-1.03% and 2.06% in the VTP-1 system, respectively. This study sheds new light on the anammox biofilm formation and provides a valid approach to initiate the DEAMOX process for low nitrogen polluted water treatment.

A novel coupling process to replace the traditional multi-stage anammox process-sulfur autotrophic denitrification (SAD) coupled anaerobic ammonium oxidation (anammox) system was designed, which solved problems of nitrate produced in anammox process and low nitrate conversion rate caused by nitrite accumulation in SAD process. Different filter structures (SAD filter and anammox granular sludge) were investigated to further explore the excellent performance of the novel integrated reactor. The results of sequential batch experiments indicated that nitrite accumulation occurred during SAD, which inhibited the conversion of nitrate to dinitrogen gas. When SAD filter and anammox granular sludge were added to packed bed reactor simultaneously, the nitrate removal rate increased by 37.21% and effluent nitrite concentration decreased by 100% compared to that achieved using SAD. The stratified filter structure solved groove flow. Different proportion influence of SAD filter and anammox granular sludge on the stratified filter structure was evaluated. More suitable ratio of SAD filter to anammox granular sludge was 2:1. Proteobacteria (57.26%), Bacteroidetes (20.12%) and Chloroflexi (9.95%) were the main phyla. The dominant genera of denitrification functional bacteria were Thiobacillus (39.80%), Chlorobaculum (3.99%), norank_f_PHOs-HE36 (2.90%) and Ignavibacterium (2.64%). The dominant genus of anammox bacterium was Candidatus_Kuenenia (3.05%).

Denitrification and anaerobic ammonium oxidation (anammox) are key processes for nitrogen removal in aquaculture, reducing the accumulated nitrogen nutrients to nitrogen gas or nitrous oxide gas. Complete removal of nitrogen from aquaculture systems is an important measure to solve environmental pollution. In order to evaluate the nitrogen removal potential of marine aquaculture ponds, this study investigated the denitrification and anammox rates, the flux of nitrous oxide (N2O) at the water-air interface, the sediment microbial community structure, and the gene expression associated with the nitrogen removal process in integrated multi-trophic aquaculture (IMTA) ponds (Apostistius japonicus-Penaeus japonicus-Ulva) with different culture periods. The results showed that the denitrification and anammox rates in sediments increased with the increase of cultivation periods and depth, and there was no significant difference in nitrous oxide gas flux at the water-air interface between different cultivation periods (p > 0.05). At the genus and phylum levels, the abundance of microorganisms related to nitrogen removal reactions in sediments changed significantly with the increase of cultivation period and depth, and was most significantly affected by the concentration of particulate organic nitrogen (PON) in sediments. The expression of denitrification gene (narG, nirS, nosZ) in surface sediments was significantly higher than that in deep sediments (p < 0.05), and was negatively correlated with denitrification rate. All samples had a certain anammox capacity, but no known anammox bacteria were found in the microbial diversity detection, and the expression of gene (hzsB) related to the anammox process was extremely low, which may indicate the existence of an unknown anammox bacterium. The data of this study showed that the IMTA culture pond had a certain potential for nitrogen removal, and whether it could make a contribution to reducing the pollution of culture wastewater still needed additional practice and evaluation, and also provided a theoretical basis for the nitrogen removal research of coastal mariculture ponds.