Stability of microbial functionality in anammox sludge adaptation to various salt concentrations and different salt-adding steps

Analysis of the regulation mechanism for salt-tolerant anammox process: process performance and metabolic insights

In this study, the start-up and microbial domestication of a salt-tolerant functional anammox system was investigated by gradually increasing the salinity level in a stabilized anammox system in the laboratory. After 44 days of stable operation, the salt-tolerant system was successfully activated, at which time the salinity of the influent water was 3 g/L, and the maximum removal efficiency of ammonia nitrogen and nitrite nitrogen in the system reached 94.18% and 96.66%, respectively, and then the ammonia nitrogen and nitrite nitrogen removal efficiency were stabilized at 88.17% and 96.48% after the enrichment domestication for 89 days. The system was operated in the salinity of 10 g/L, with the concentration of each nitrogen compound measured at the same time. The ammonia nitrogen removal efficiency decreased to 59.93% at a salinity of 10 g/L, which had a significant impact on the system. High-throughput sequencing revealed that the system was enriched with a large number of Chloroflexi, the relative abundance of which increased from 19.46% to 52.33%, and the genus of AnAOB was transformed from Candidatus Brocadia to Candidatus Kuenenia, Candidatus Kuenenia, with a percentage of 4.78%. The system successfully achieved the simultaneous removal of ammonia nitrogen and nitrite nitrogen under salinity stress, which to a certain extent indicated that AnAOB could achieve the initiation and enrichment domestication under salinity conditions, and could provide a basis for the efficient and low-consumption treatment of high salinity nitrogen-containing wastewater.HighlightsAnammox reaction can be successfully initiated under low salinity conditionsSalinity of 10 g/L has a severe shock effect on the anammox systemAfter salinity enrichment and domestication, the abundance of norank_f__norank__o___SBR1031 and Candidatus Kuenenia in the anammox reaction reached 26.7% and 4.78%, respectively.

Interspecific competition and adaptation of anammox bacteria at different salinities: Experimental validation of the Monod growth model with salinity inhibition

Ecological niche segregation of anaerobic ammonium oxidizing (anammox) bacteria under saline environments remains unresolved despite its ecological and practical importance. In this study, niche segregation by salinity for Ca. Brocadia sinica, Ca. Jettenia caeni, Ca. Kuenenia stuttgartiensis and Ca. Scalindua sp. was systematically studied. The inhibitory effect of salinity on specific anammox activity (SAA) was measured experimentally and model-fitted to obtain the salinity-dependent maximum specific growth rates (µmax). The resulting µmax were incorporated into a Monod growth model with nitrite as the limiting substrate to predict which anammox bacterial species would dominate at a given salinity. The model predictions revealed that there were threshold salinity ranges where specific growth rates were comparable and the determining factor for the dominant species was the availability of nitrite. Ca. B sinica, Ca. J. caeni, and Ca. K. stuttgartiensis could compete at 0 - 0.5% salinity, while Ca. K. stuttgartiensis and Ca. Scalindua sp. could coexist at around 2% salinity. The model prediction was validated by conducting interspecific competition experiments among the four anammox species in nitrite-limiting membrane bioreactors (MBRs) under different salinity concentrations. The interspecific competition experiments showed that Ca. K. stuttgartiensis with relatively high affinity for nitrite was dominant at a wide range of salinities from 0.25 to 1.75%. Outside this salinity range, Ca. B. sinica was dominant at salinity 0 %, and Ca. Scalindua sp. outcompeted exclusively the other species due to its high salinity tolerance at salinities above 2.0%. These experimental results are in good agreement with the model predictions, demonstrating the validity of the Monod model in accounting for salinity inhibition and reflecting the salinity-dependent distributions of anammox bacteria reported in a variety of engineered and natural saline environments.

Chemomixoautotrophy and stress adaptation of anammox bacteria: A review

Anaerobic ammonium oxidizing (anammox) bacteria, which were first discovered nearly three decades ago, are crucial for treating ammonium-containing wastewater. Studies have reported on the biochemical nitrogen conversion process and the physiological, phylogenic, and ecological features of anammox bacteria. For a long time, anammox bacteria were assumed to have a lithoautotrophic lifestyle. However, recent studies have suggested the functional versatility of anammox bacteria. Genome-based analysis and experiments with enrichment cultures have demonstrated the association of the metabolic activities of anammox bacteria with different stress conditions, revealing the importance of utilizing specific organic substances, including organoautotrophy, for growth and adaptation to stress conditions. Our understanding regarding the utilization and metabolism of organic substances and their associations with anammox reactions in anammox bacteria is growing but still incomplete. In this review, we summarize the effect of the utilization of organic substances by anammox bacteria under environmental stress conditions, emphasizing their potential organoautotrophic activity and metabolic flexibility. Although most anammox bacteria may utilize specific organic substances, Ca. Brocadia exhibited the highest level of mixoautotrophic activity. The environmental factors that substantially affect the organoautotrophic activities of anammox bacteria were also examined. This review provides a new perspective on the organoautotrophic capacity of anammox bacteria.

Enhancing microbial salt tolerance through low-voltage stimulation for improved p-chloronitrobenzene (p-CNB) removal in high-salinity wastewater

As an important raw material for the synthesis of chemical and pharmaceutical, hazardous carcinogen p-chloronitrobenzene (p-CNB) has been widely found in high-salinity wastewater which need to be treated carefully. Due to the high-salinity shock on microorganisms, conventional microbial treatment technologies usually show poor effluent quality. This study initially investigated the p-CNB removal performance of microorganisms stimulated by 1.2 V low-voltage in high-salinity wastewater under facultative anaerobic conditions and further revealed the enhanced mechanisms. The results showed that the p-CNB removal kinetic parameter kp-CNB in the electrostimulating microorganism reactor (EMR) increased by 104.37 % to 155.30 % compared to the microorganism reactor (MR) as the control group under the varying salinities (0-45 g/L NaCl). The secretion of extracellular polymeric substances (EPS) in halotolerant microorganisms mainly enhanced by 1.2 V voltage stimulation ranging from 0 g/L NaCl to 30 g/L NaCl. Protein concentration ratio of EMR to MR in loosely bound EPS achieved maximum value of 1.77 at the salinity of 15 g/L NaCl, and the same ratio in tightly bound EPS also peaked at 1.39 under the salinity of 30 g/L NaCl. At the salinity of 45 g/L NaCl, 1.2 V voltage stimulation mainly enhanced salt-in strategy of halotolerant microorganisms, and the intracellular Na+ and K+ concentration ratio of EMR to MR reached maximum and minimum values of 0.65 and 1.92, respectively. Furthermore, the results of microbial metagenomic and metatranscriptomic analysis showed the halotolerant microorganisms Pseudomonas_A and Nitratireductor with p-CNB removal ability were enriched significantly under 1.2 V voltage stimulation. And the gene expression of p-CNB removal, salt-in strategy and betaine transporter were enhanced under voltage stimulation at varying salinities. Our investigation provided a new solution which combined with 1.2 V voltage stimulation and halotolerant microorganisms for the treatment of high-salinity wastewater.

Long-term adaptation of two anammox granules with different ratios of Candidatus Brocadia and Candidatus Jettenia under increasing salinity and their application to treat saline wastewater

Nitrogen removal in saline wastewater is a challenge of the anaerobic ammonium oxidation (anammox) process, which is dominated by freshwater anammox bacteria (FAB). Candidatus Brocadia and Candidatus Jettenia, the most widely used FABs, have been separately applied and evaluated for their ability to treat saline wastewater. To understand the effect of salinity on nitrogen removal capability when they present together in an anammox granule, we compared two anammox granules: GRN1 was evenly dominated by Ca. Brocadia (42 %) and Ca. Jettenia (43 %), while GRN2 was dominated with mostly Ca. Brocadia (90 %) and a small amount of Ca. Jettenia (1 %). Each granule was inoculated into a continuous column reactor to treat artificial wastewater containing 150 mg NH₄⁺-N/L and 150 mg NO₂^--N/L under increasing saline conditions for 250 days. GRN1 showed superior and more stable nitrogen removal than GRN2 under saline conditions of up to 15 g NaCl/L. Under high-saline conditions, both the granules' sizes decreased (larger GRN1 than GRN2 in initial). The mass percent of Na salt increased (more in GRN2) and mineral contents decreased more in GRN1. High-throughput sequencing for microbial community analysis showed that Planctomycetes in GRN1 (85 %) and GRN2 (92 %) decreased to 14 % and 12 %, respectively. The ratio of Ca. Brocadia and Ca. Jettenia in GRN1 changed to 37 % and 63 %, respectively, whereas the ratio in GRN2 (99 % and 1 %, respectively) did not change. Both salt-adapted granules were applied to the two-stage partial nitritation and anammox (PN/A) process to treat high strength ammonium (400 mg/L) wastewater under high saline condition (15 g NaCl/L). The PN/A process containing GRN1 showed more stable nitrogen removal performance during approximately 100 days of operation. These results suggest that the anammox granules evenly dominated by two FABs, Ca. Brocadia and Ca. Jettenia, would be advantageous to treat high-strength NH₄⁺ wastewater under high-saline conditions.

Metagenomic analysis and nitrogen removal performance evaluation of activated sludge from a sequencing batch reactor under different salinities

The effect of salinity on the nitrogen removal performance and microbial community of activated sludge was investigated in a sequencing batch reactor. The NH₄⁺-N removal efficiency was over 95% at 0-4% salinity, indicating that the nitrification performance of activated sludge was slightly affected by lower salinity. The obvious nitrite accumulation was observed with the increment of the salinity to 5%, followed by a notable decline in the nitrogen removal performance at 6% salinity. The salinity inhibited the microbial activity, and the specific rate of nitrification and denitrification was decreased by the increasing salinity obviously. Additionally, the lower activity of superoxide dismutase and peroxidase and higher reactive oxygen species content in activated sludge might account for the deteriorative nitrogen removal performance at 6% salinity. Metagenomics analysis revealed that the genes encoding the ABC-type quaternary amine transporter in the ABC transporter pathway were abundant in the activated sludge at 2% and 4% salinity, and the higher salinity of 6% led to the loss of the genes encoding the p-type Na⁺ transporter in the ABC transporter pathway. These results indicated that the salinity could weaken the ABC transporter pathway for the balance of osmotic pressure in activated sludge. The microbial activity and nitrogen removal performance of activated sludge were decreased due to the unbalanced osmotic pressure at higher salinity.

Response of denitrifying anaerobic methane oxidation enrichment to salinity stress: Process and microbiology

Denitrifying anaerobic methane oxidation (DAMO) is a novel biological process which could decrease nitrogen pollution and methane emission simultaneously in wastewater treatment. Salinity as a key environmental factor has important effects on microbial community and activity, however, it remains unclear for DAMO microorganisms. In this study, response of the enrichment of DAMO archaea and bacteria to different salinity was investigated from the aspect of process and microbiology. The results showed that the increasing salinity from 0.14% to 25% evidently deteriorated DAMO process, with the average removal rate of nitrate and methane decreased from 1.91 mg N/(L·d) to 0.07 mg N/(L·d) and 3.22 μmol/d to 0.59 μmol/d, respectively. The observed IC₅₀ value of salinity on the DAMO culture was 1.73%. Further microbial analyses at the gene level suggested that the relative abundance of DAMO archaea in the enrichment decreased to 46%, 39%, 38% and 33% of the initial value. However, DAMO bacteria suffered less impact with the relative abundance maintaining over 75% of the initial value (except 1% salinity). In functional genes of DAMO bacteria, pmoA, decreased gradually from 100% to 86%, 43%, 15% and 2%, while mcrA (DAMO archaea) maintained at 67%-97%. This difference probably indicated DAMO bacteria appeared functional inhibition prior to community inhibition, which was opposite for the DAMO archaea. Results above-mentioned concluded that, though the process of nitrate-dependent anaerobic methane oxidation was driven by the couple of DAMO archaea and bacteria, they individually featured different response to high salinity stress. These findings could be helpful for the application of DAMO-based process in high salinity wastewater treatment, and also the understanding to DAMO microorganisms.

Glutamate Enhances Osmoadaptation of Anammox Bacteria under High Salinity: Genomic Analysis and Experimental Evidence

An osmoprotectant that alleviates the bacterial osmotic stress can improve the bioreactor treatment of saline wastewater. However, proposed candidates are expensive, and osmoprotectants of anammox bacteria and their ecophysiological roles are not fully understood. In this study, a comparative analysis of 34 high-quality public metagenome-assembled genomes from anammox bacteria revealed two distinct groups of osmoadaptation. Candidatus Scalindua and Kuenenia share a close phylogenomic relation and osmoadaptation gene profile and have pathways for glutamate transport and metabolisms for enhanced osmoadaptation. The batch assay results demonstrated that the reduced Ca. Kuenenia activity in saline conditions was substantially alleviated with the addition and subsequent synergistic effects of potassium and glutamate. The operational test of two reactors demonstrated that the reduced anammox performance under brine conditions rapidly recovered by 35.7-43.1% as a result of glutamate treatment. The Ca. Kuenenia 16S rRNA and hydrazine gene expressions were upregulated significantly (p < 0.05), and the abundance increased by approximately 19.9%, with a decrease in dominant heterotrophs. These data demonstrated the effectiveness of glutamate in alleviating the osmotic stress of Ca. Kuenenia. This study provides genomic insight into group-specific osmoadaptation of anammox bacteria and can facilitate the precision management of anammox reactors under high salinity.

Osmotic stress tolerance and transcriptome analysis of Gluconobacter oxydans to extra-high titers of glucose

Gluconobacter oxydans has been widely acknowledged as an ideal strain for industrial bio-oxidations with fantastic yield and productivity. Even 600 g/L xylose can be catalyzed efficiently in a sealed and compressed oxygen-supplying bioreactor. Therefore, the present study seeks to explore the osmotic stress tolerance against extra-high titer of representative lignocellulosic sugars like glucose. Gluconobacter oxydans can well adapted and fermented with initial 600 g/L glucose, exhibiting the highest bio-tolerance in prokaryotic strains and the comparability to the eukaryotic strain of Saccharomyces cerevisiae. 1,432 differentially expressed genes corresponding to osmotic pressure are detected through transcriptome analysis, involving several genes related to the probable compatible solutes (trehalose and arginine). Gluconobacter oxydans obtains more energy by enhancing the substrate-level phosphorylation, resulting in the increased glucose consumption rate after fermentation adaption phase. This study will provide insights into further investigation of biological tolerance and response to extra-high titers of glucose of G. oxydans.

Combined machine learning and biomolecular analysis for stability assessment of anaerobic ammonium oxidation under salt stress

In this study, the stability of the total nitrogen removal efficiency (TNRE) was modeled using an artificial neural network (ANN)-based binary classification model for the anaerobic ammonium oxidation (AMX) process under saline conditions. The TNRE was stabilized to 80.2 ± 11.4% at the final phase under the salinity of 1.0 ± 0.02%. The results of terminal restriction fragment length polymorphism (T-RFLP) analysis showed the predominance of Candidatus Jettenia genus. Real-time quantitative PCR analysis revealed the average abundance of Ca. Jettenia and Kuenenia spp. increased in 3.2 ± 5.4 × 10⁸ and 2.0 ± 2.2 × 10⁵ copies/mL, respectively. The prediction accuracy using operational parameters with data augmentation was 88.2%. However, integration with T-RFLP and real-time qPCR signals improved the prediction accuracy by 97.1%. This study revealed the feasible application of machine learning and biomolecular signals to the stability prediction of the AMX process under increased salinity.

Can anammox process be adopted for treating wastewater with high salinity exposure risk?

Anammox was a promising technology for nitrogen removal, and has been applied for treating many kinds of nitrogenous wastewaters. Considering the risk in high salinity of the municipal sewage in coastal city, the feasibility of Anammox process for treating low ammonia wastewater (around 50 mg L^-1) with increasing salinity was investigated in this study. The results showed that the salinity in low concentrations (1-5 g L^-1) had slight impact on the nitrogen removal and activity of Anammox bacteria but significantly improved its growth. The moderate salinity (10-40 g L^-1) decreased the specific Anammox activity (SAA) to 8.11 from the initial 13.15 mg N g^-1 SS h^-1, but increased the abundance to 52.3% from 30.1% (Candidatus Kuenenia). High salinity (50-60 g L^-1) performed severe inhibition on activity and abundance both, with the SAA decreased to 0 and abundance to 11.9%. The self-recovery performance was unsatisfactory when salinity was unavailable. A quadratic curve between the SAA and salinity concentration was fitted, and the IC₅₀ was calculated as 42.1 g L^-1 (NaCl). Anammox process could be directly adopted for treating low ammonia sewage with low salinity, whereas activity enhancement or adaption improvement should be pre-presented for treating sewage with moderate or high salinity.

Low strength wastewater anammox start-up by stepwise decrement in influent nitrogen: Biofilm formation mechanism and mathematical modelling

The application of mainstream anammox process is hampered by its overlong start-up and instability under disturbance. A lab-scale mainstream anammox moving bed biofilm reactor (MBBR) was successfully started in 120 days with stepwise decrement in influent nitrogen concentration from sidestream to mainstream condition. The initial colonization by Candidatus Jettenia and filamentous fermenter Anaerolineaceae were potentially mediated by hydrophobic interaction and type IV pilus. Ca. Kuenenia with higher substrate affinity outcompeted Ca. Jettenia, and the predominant fermenters shifted to fermentative Ignavibacteriaceae in the mature biofilm. A novel mainstream anammox biofilm development (MABD) model was constructed to describe biofilm growth, population dynamics, and nitrogen removal performance. The simulation results suggested that higher inocula biomass (460-690 mgVSS·L^-1), relative abundance of low-affinity AnAOB in the inocula (e.g., Ca. Jettenia, 1.3-2%), and the early-stage solids retention time (45-68 days) were desired to form thicker biofilm and improve effluent quality during 120-day mainstream anammox MBBR start-up. The mechanistic insights into biofilm formation and predictive power of the newly developed MABD model are of importance to the design and operation of mainstream anammox processes towards more biofilm biomass and higher nitrogen removal efficiency.

Topography effect on Aspergillus flavus occurrence and aflatoxin B1 contamination associated with peanut

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Topography is a major factor affecting the enrichment of Aspergillus flavus and aflatoxin contamination.

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Aflatoxin contamination can damage the diversity and function of microorganisms on peanut.

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The population structure and function of microbiome were more abundant in the aflatoxin low contamination area.

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The soil physicochemical factors can regulate the structure and function of microorganisms of peanut pods.

Aflatoxin B₁ is a strong carcinogenic and toxic fungal toxin produced by Aspergillus flavus and other Aspergillus species, and can seriously threaten the health of consumers and the safety and quality of agricultural products. Aspergillus in agricultural products are closely related to topography and symbiotic microbes. It is not fully clear that how topography affects the assembly process of A. flavus and symbiotic fungi on plant. In this study, we analyzed the structure and assembly process of fungi on the peanut. We also performed the metatranscriptome analysis, identified the functional genes and metabolic pathways enriched in both A. flavus and its symbiotic fungi. In our experiment, terrain and soil properties could significantly affect the gene expression of microbiome, A. flavus abundance and infection ability to peanuts. Meanwhile, the Permanova correlation analysis revealed that differentially expressed genes were strongly correlated with the soil physicochemical factors. Furthermore, metabolomic analysis identified the main metabolites associated with A. flavus and aflatoxin B₁, the results proved that the terrain significantly affected the microorganisms associated with peanut pods to produce a variety of metabolites. In conclusion, our results indicate that topography can significantly influence the assembly process of A. flavus and microorganisms, the activation of functional genes and metabolic pathways, the enrichment of aflatoxin-producing fungi.

Adaptation, restoration and collapse of anammox process to La(III) stress: Performance, microbial community, metabolic function and network analysis

During the mining of rare earth mineral, the use of lanthanum-containing fertilizers, and the disposal of lanthanum-containing electronic products, the content of lanthanum (La(III)) in typical ammonia wastewater with low carbon to nitrogen ratio is increasing day by day. Here, effects of La(III) on anammox process in performance, microbial community structure, metabolic function, and microbial co-occurrence network were investigated. The results shown that the nitrogen removal efficiency was declines briefly and then gradually recovers after low dosage (1-5 mg/L) La(III) treatment and the decrease to low level (24.25 ± 1.74%) under high La(III) dosage (10 mg/L). La(III) in the range of 1-5 mg/L significantly promoted the relative abundance of Anammoxoglobus (0.024% to 9.762%). The blocking of key metabolic pathways was confirmed to cause the breakdown of anammox by PICRUSt. Furthermore, network analysis revealed that lack of cooperation bacteria limits the activity of Anammoxoglobus.

Biostimulation of a marine anammox bacteria-dominated bioprocess by Co(II) to treat nitrogen-rich, saline wastewater

The biostimulation of a marine anammox bacteria (MAB)-dominated bioprocess with Co(II) was studied in a sequencing batch reactor (SBR) treating nitrogen-rich saline wastewater at 15 °C. The low Co(II) load of 0.0015 kgCo²⁺_added/(m^3.d) had little effect on the removal of nitrogen. The nitrite removal rate (NRR), ammonia removal rate (ARR), and specific anammox activity (SAA) reached 0.73 kg/(m³·d), 0.59 kg/(m³·d), and 0.23 kg/(kg·d), respectively, under the Co(II) load of 0.009 kgCo²⁺_added/(m^3.d). However, the loadings of Co(II) at 0.024-0.03 kgCo²⁺_added/(m^3.d) negatively affected the activity of MAB. Besides, the values of ΔNO₂^--N/ΔNH₄⁺-N (1.15-1.29) were lower than the theoretical ratio values (around 1.32) likely because of the marine commamox process. The removal of nitrogen from nitrogen-rich saline wastewater was achieved by the synergy between Candidatus Scalindua (27.11%) and Candidatus Kuenenia (9.55%). The nitrogen removal with Co(II) addition could be well described by a modified Logistic model.