Antimicrobial peptide antibiotics inhibit aerobic denitrification via affecting electron transportation and remolding carbon metabolism

Comprehensive revealing the destructive effect and inhibitory mechanism of oxytetracycline on aerobic denitrification bacteria Acinetobacter sp. AD1 based on cell state, electron behavior and intracellular environment

The wide application and low utilization rate of oxytetracycline (OTC) make it often detected in wastewater, which may cause harmful effects on microbial denitrification. Aerobic denitrification (AD) as a new microbial denitrification technology has obvious advantages. However, systematic studies on the effects of OTC on it are lacking. In this study, the effect of OTC on AD was comprehensively explored from multiple perspectives, the main results are as follows. From the perspective of bacterial performance, OTC inhibited AD bacteria growth, denitrification efficiency, and caused serious damage to cell morphological structure, results of CCK-8 confirmed that bacterial activity was significantly affected. From the perspective of electron behavior, OTC decreased electron-producing capacity of carbon metabolism, reduced activity of the electron transport system, inhibited the electron consumption of NAR and NIR to varying degrees, thus increased the risk of nitrite accumulation. From the perspective of intracellular environment, OTC broke redox balance and antioxidant mechanism, related carbon and nitrogen cycle functional genes were down-regulated, affected amino acid, organic acid and nucleotide metabolic processes. The above results provide important information for evaluating the potential risks of antibiotics on the application of AD, and provide key background and theoretical support for stabilizing the technology.

Bioremediation potential of sulfadiazine-degrading bacteria: Impacts on ryegrass growth and soil functionality

The extensive use of antibiotics, particularly sulfadiazine (SDZ), has led to significant environmental contamination and the proliferation of antibiotic resistance genes (ARGs). This study investigates the bioremediation potential of two SDZ-degrading bacterial strains, Acinetobacter sp. M9 and Enterobacter sp. H1, and their impact on ryegrass (Lolium perenne) growth and the inter-root microenvironment in SDZ-contaminated soils. A pot experiment combined with amplicon and metagenomic sequencing revealed that inoculation with M9 and H1 significantly enhanced ryegrass growth by alleviating oxidative stress, increasing chlorophyll content, and improving soil nutrient availability. The strains also promoted SDZ degradation efficiency and improved carbon and nitrogen cycling through the upregulation of key functional genes. Furthermore, microbial community analysis demonstrated increased alpha diversity, shifts in dominant taxa, and functional enrichment in pollutant degradation pathways. The dynamics of ARGs revealed a decrease in aminoglycoside, rifamycin, and streptomycin resistance genes, while sulfonamide resistance genes increased due to the residual SDZ stress. These findings highlight the potential of M9 and H1 as sustainable bioremediation agents to mitigate antibiotic contamination, improve soil health, and support plant growth in polluted environments.

Carbon source driven microbial ecological behaviors achieving efficient synchronous elimination of nitrogen and sulfamethoxazole within MABR

As carbon source shaped microbial ecosystem, the limited information on microbial ecological behaviors and ecological interrelationships between nitrogen and antibiotics metabolism under carbon source blocked the achievement of efficient synchronous nitrogen and antibiotics removal. Four typical carbon sources were selected to investigate their impact on nitrogen and sulfamethoxazole (SMX) metabolism in a membrane-aerated biofilm reactor (MABR) system. Detailed ecological insights were obtained, including degradation pathways, microbiota composition, functional genes, and microbial interactions. The microbial community's carbon source preferences related to nitrogen and SMX metabolism, as well as their interrelationships under different carbon sources, were elucidated. Specifically, sucrose, providing a "gradual-releasing" energy source, promoted the abundance of Chryseobacterium and Paenarthrobacter, which facilitated the cleavage of the S-N bond in SMX and generated more small-molecule metabolites, enhancing SMX removal. Acetate, serving as a "first aid" energy source, resulted in multiple nitrogen metabolic pathways, leading to efficient nitrogen removal. Further, ecological networks revealed that sucrose caused superior SMX removal by enhancing metabolites cross-feeding between keystone N-cycling microbes (e.g., Paracoccus, Bdellovibrio) and keystone SMX degraders (e.g., Mycobacterium, Nocardioide), while acetate induced excellent nitrogen removal as it resulted in intensive complexity and connectivity within microbial ecosystem. Structural equation models (SEMs) analysis confirmed the dominant contribution of ecological networks complexity and cross-feeding on nitrogen and SMX removal than other ecological features. Based on fundamental insights, it was demonstrated that the acetate and sucrose mixture achieved more efficient SMX and nitrogen removal.

Rational design of peptides to overcome drug resistance by metabolic regulation

Chemotherapy is widely used clinically, however, its efficacy is often compromised by the development of drug resistance, which arises from prolonged administration of drugs or other stimuli. One of the driven causes of drug resistance in tumors or bacterial infections is metabolic reprogramming, which alters mitochondrial metabolism, disrupts metabolic pathways and causes ion imbalance. Bioactive peptide materials, due to their biocompatibility, diverse bioactivities, customizable sequences, and ease of modification, have shown promise in overcoming drug resistance. This review provides an in-depth analysis of metabolic reprogramming and associated microenvironmental changes that contribute to drug resistance in common tumors and bacterial infections, suggesting potential therapeutic targets. Additionally, we explore peptide-based materials for regulating metabolism and their potential synergic effect with other therapies, highlighting the mechanisms by which these peptides reverse drug resistance. Finally, we discuss future perspectives and the clinical challenges in peptide-based treatments, aiming to offer insights for overcoming drug-resistant diseases.

Molecular ecological insights into the synergistic response mechanism of nitrogen transformation, electron flow and antibiotic resistance genes in aerobic activated sludge systems driven by sulfamethoxazole and/or trimethoprim stresses

The prevalence of antibiotics poses a serious challenge to biological nitrogen removal in wastewater. In this study, the effects of sulfamethoxazole and/or trimethoprim (15 mg/L∼30 mg/L) on treatment performance, nitrogen transformation and antibiotic resistance genes (ARGs) were investigated in aerobic activated sludge systems to elucidate the metabolic mechanism under high antibiotic stress. 15 mg/L single antibiotic stress improved total nitrogen removal performance due to the persistence of nitrifiers and enrichment of denitrifiers, with an optimum removal efficiency of 96.5 %. Up-regulation of all denitrifying genes, coupled with enhanced electron transfer of Complex II and III, contributed to the emergence of aerobic denitrification. The increased expression of antioxidant genes also alleviated intracellular pressure. Whereas combined antibiotic stress induced the significant down-regulation of denitrifying bacteria and genes (nirKS and nosZ), and suppressed the electron supply for denitrification by restraining genes related to Complex Ⅰ and energy supply by tricarboxylic acid cycle, driving the collapse of activated sludge system, with ammonia and total nitrogen removal efficiencies dropping to below 40 % and 20 %, respectively. The dominant genera in system changed from TM7a to Thiothrix and Sphaerotilus with increasing antibiotic concentration and type. Moreover, antibiotic stress promoted a slight enrichment of ARGs, especially those encoding efflux mechanisms. Cooperative relationships (> 93 %) dominated among ARGs, and Klebsiella was identified as the crucial host. ARGs regulating antibiotic efflux were more likely to be co-expressed with functional genes. These results may provide a theoretical basis for establishing promising strategies to mitigate antibiotic-caused process deterioration.

Simultaneous degradation of roxithromycin and nitrogen removal by Acinetobacter pittii TR1: Performances, pathways, and mechanisms

Pharmaceutical and aquaculture wastewater contains not only antibiotics but also high concentrations of nitrogen, but few studies have been conducted on bacteria that target this complex pollution for degradation. A novel heterotrophic nitrifying aerobic denitrifying (HN-AD) strain Acinetobacter pittii TR1 isolated from soil. When the C/N ratio was 20, the strain could degrade 50 mg/L roxithromycin (ROX) and the nitrogen removal rate was 96.06% with no accumulation of nitrite. The nitrogen metabolism pathway of strain TR1 was conjectured by NH4+-N → (NH2OH) → NO2--N → NO3--N → NO2--N → (NO → N2O → N2). Nitrogen balance analysis showed that 50.43% of the initial total nitrogen (TN) was converted to gaseous nitrogen and 45.39% was assimilated by TR1. Lower concentrations of ROX affected the activity of key enzymes, and the expression of the denitrifying genes hao, napA, nirK, norZ, and nosZ were significantly up-regulated, with the gene expression of nirK being up-regulated by 15.9-fold. Cleavage of desosamine, demethylation, and phosphorylation were the main biotransformation pathways of ROX. This work offers fresh insights into the metabolic processes of HN-AD bacteria under antibiotic stress, as well as evidence supporting strain TR1 in the treatment of wastewater with nitrogen and ROX.

Synthetic peptides bioactive against phytopathogens have lower impact on some beneficial bacteria: An assessment of peptides biosafety in agriculture

The emergence of bacterial resistance and the increasing restrictions on the use of agrochemicals are boosting the search for novel, sustainable antibiotics. Antimicrobial peptides (AMPs) arise as a new generation of antibiotics due to their effectiveness at low doses and biocompatibility. We compared the antimicrobial activity of four promising AMPs (CA-M, BP100, RW-BP100, and 3.1) against a collection of notorious phytopathogens, and quantified their impact on plant beneficial bacteria. Plant growth promoters (PGP) and biological control agents (BCA) were also included to study the feasibility of integrating AMPs with bio-based strategies to mitigate diseases impacts and promote crop production. Flow cytometry and fluorescence microscopy revealed that the AMPs' effects on the membrane integrity of both gram-negative and gram-positive strains were time- and concentration-dependent. Bacterial strains were separated into three groups of susceptibility to the AMPs. Group 1 was represented by the most sensitive, gram-negative phytopathogenic belonging to Xanthomonadales and Pseudomonadales and the gram-positive C. michiganensis subsp. michiganensis. Group 2 encompassed bacteria showing intermediate susceptibility, namely P. carotovorum subsp. carotovorum, P. cerasi, both phytopathogens, as well as the plant growth promoters P. fluorescens and P. putida. Finaly, Group 3 was represented by the bacteria with the lowest susceptibility to AMPs. It included beneficial bacteria (B. zhangzhouensis, B. subtilis, B. safensis, P. azotoformans), a phytopathogen (R. solanacearum), and a strain reported as able to act as both (P. aeruginosa). This work demonstrates that the minimum inhibitory concentrations (MICs) needed to act against the beneficial Bacillus and Pseudomonas strains were higher than those needed to produce bacteriostatic or bactericidal effects on the phytopathogens tested, hence supporting that these AMPs might be environmentally safe antibiotics with low likeliness of disrupting the beneficial microbial communities. The possibility of mixing these AMPs with BCA/PGP, in a combined biocontrol strategy, is also discussed.

External circuit loading mode regulates anode biofilm electrochemistry and pollutants removal in microbial fuel cells

This study investigated the effects of different external circuit loading mode on pollutants removal and power generation in microbial fuel cells (MFC). The results indicated that MFC exhibited distinct characteristics of higher maximum power density (Pmax) (named MFC-HP) and lower Pmax (named MFC-LP). And the capacitive properties of bioanodes may affect anodic electrochemistry. Reducing external load to align with the internal resistance increased Pmax of MFC-LP by 54.47 %, without no obvious effect on MFC-HP. However, intermittent external resistance loading (IER) mitigated the biotoxic effects of sulfamethoxazole (SMX) (a persistent organic pollutant) on chemical oxygen demand (COD) and NH4+-N removal and maintained high Pmax (424.33 mW/m2) in MFC-HP. Meanwhile, IER mode enriched electrochemically active bacteria (EAB) and environmental adaptive bacteria Advenella, which may reduce antibiotic resistance genes (ARGs) accumulation. This study suggested that the external circuit control can be effective means to regulate electrochemical characteristics and pollutants removal performance of MFC.

Heterotrophic nitrification processes driven by glucose and sodium acetate: New insights into microbial communities, functional genes and nitrogen metabolism from metagenomics and metabolomics

Heterotrophic nitrification (HN) bacteria use organic carbon sources to remove ammonia nitrogen (NH4+-N); however, the mechanisms of carbon and nitrogen metabolism are unknown. To understand this mechanism, HN functional microbial communities named MG and MA were enriched with glucose and sodium acetate, respectively. The NH4+-N removal efficiencies were 98.87 % and 98.91 %, with 88.06 % and 69.77 % nitrogen assimilation for MG and MA at 22 h and 10 h, respectively. Fungi (52.86 %) were more competitive in MG, and bacteria (99.99 %) were dominant in MA. Metagenomic and metabolomic analyses indicated that HN might be a signaling molecule (NO) in the production and detoxification processes when MG metabolizes glucose (amo, hao, and nosZ were not detected). MA metabolizes sodium acetate to produce less energy and promotes nitrogen oxidation reduction; however, genes (hao, hox, and NOS2) were not detected. These results suggest that NO and energy requirements induce microbial HN.

How denitrifiers defense ciprofloxacin: Insights from intracellular and extracellular stress response

Overuse of antibiotics has led to their existence in nitrogen-containing water. The impacts of antibiotics on bio-denitrification and the metabolic response of denitrifiers to antibiotics are unclear. We systematically analyzed the effect of ciprofloxacin (CIP) on bio-denitrification and found that 5 mg/L CIP greatly inhibited denitrification with a model denitrifier (Paracoccus denitrificans). Nitrate reduction decreased by 32.89 % and nitrous oxide emission increased by 75.53 %. The balance analysis of carbon and nitrogen metabolism during denitrification showed that CIP exposure blocked electron transfer and reduced the flow of substrate metabolism used for denitrification. Proteomics results showed that CIP exposure induced denitrifiers to use the pentose phosphate pathway more for substrate metabolism. This caused a substrate preference to generate NADPH to prevent cellular damage rather than NADH for denitrification. Notably, despite denitrifiers having antioxidant defenses, they could not completely prevent oxidative damage caused by CIP exposure. The effect of CIP exposure on denitrifiers after removal of extracellular polymeric substances (EPS) demonstrated that EPS around denitrifiers formed a barrier against CIP. Fluorescence and infrared spectroscopy revealed that the binding effect of proteins in EPS to CIP prevented damage. This study shows that denitrifiers resist antibiotic stress through different intracellular and extracellular defense strategies.

Deciphering the potential role of quorum quenching in efficient aerobic denitrification driven by a synthetic microbial community

Low efficiency is one of the main challenges for the application of aerobic denitrification technology in wastewater treatment. To improve denitrification efficiency, a synthetic microbial community (SMC) composed of denitrifiers Acinetobacter baumannii N1 (AC), Pseudomonas aeruginosa N2 (PA) and Aeromonas hydrophila (AH) were constructed. The nitrate (NO3--N) reduction efficiency of the SMC reached 97 % with little nitrite (NO2--N) accumulation, compared to the single-culture systems and co-culture systems. In the SMC, AH proved to mainly contribute to NO3--N reduction with the assistance of AC, while PA exerted NO2--N reduction. AC and AH secreted N-hexanoyl-DL-homoserine lactone (C6-HSL) to promote the electron transfer from the quinone pool to nitrate reductase. The declined N-(3-oxododecanoyl)-L-homoserine lactone (3OC12-HSL), resulting from quorum quenching (QQ) by AH, stimulated the excretion of pyocyanin, which could improve the electron transfer from complex III to downstream denitrifying enzymes for NO2--N reduction. In addition, C6-HSL mainly secreted by PA led to the up-regulation of TCA cycle-related genes and provided sufficient energy (such as NADH and ATP) for aerobic denitrification. In conclusion, members of the SMC achieved efficient denitrification through the interactions between QQ, electron transfer, and energy metabolism induced by N-acyl-homoserine lactones (AHLs). This study provided a theoretical basis for the engineering application of synthetic microbiome to remove nitrate wastewater.

Metagenomic insights into the nitrogen metabolism, antioxidant pathway, and antibiotic resistance genes of activated sludge from a sequencing batch reactor under tetracycline stress

Tetracycline is prevalent in wastewater treatment plants and poses a potential threat to biological nitrogen removal under long-term exposure. In the present study, the influence of different tetracycline concentrations on the nitrogen removal, bioactivity response, and the spread of antibiotic resistance genes (ARGs) was assessed in sequencing batch reactor (SBR). The nitrogen removal efficiency, nitrification rate, and denitrification rate and their corresponding enzymatic activities gradually decreased with an increase in tetracycline concentration from 0.5 to 15 mg/L. The remarkable toxicity induced by tetracycline led to a significant increase in the peroxidation and the response of antioxidant system, as evidenced by strengthened antioxidant enzymatic activity and abundant genes (SOD12, katG, PXDN, gpx, and apx). Tetracycline addition significantly inhibited the ammonia-oxidizing bacterium Nitrosomonas and functional genes (amoA, amoB, and amoC). The presence of tetracycline decreased the abundance of citrate synthase and genes (CS, IDH3, and acnA) and interfered with carbon source metabolism, leading to impaired bioactivity and treatment performance. In addition, the presence of tetracycline induces diversity and differences in ARGs. The results provide reliable basic data for a deeper understanding of the effects of tetracycline on the nitrogen removal performance of bioreactors and provide a theoretical basis to build a promising strategy for relieving antibiotic-caused process fluctuations.

Comprehensive metagenomic and enzyme activity analysis reveals the inhibitory effects and potential toxic mechanism of tetracycline on denitrification in groundwater

The widespread use of tetracycline (TC) inevitably leads to its increasing emission into groundwater. However, the potential risks of TC to denitrification in groundwater remain unclear. In this study, the effects of TC on denitrification in groundwater were systematically investigated at both the protein and gene levels from the electron behavior aspect for the first time. The results showed that increasing TC from 0 to 10 µg·L-1 decreased the nitrate removal rate from 0.41 to 0.26 mg·L-1·h-1 while enhancing the residual nitrite concentration from 0.52 mg·L-1 to 50.60 mg·L-1 at the end of the experiment. From a macroscopic view, 10 µg·L-1 TC significantly inhibited microbial growth and altered microbial community structure and function in groundwater, which induced the degeneration of denitrification. From the electron behavior aspect (the electron production, electron transport and electron consumption processes), 10 µg·L-1 TC decreased the concentration of electron donors (nicotinamide adenine dinucleotide, NADH), electron transport system activity, and denitrifying enzyme activities at the protein level. At the gene level, 10 µg·L-1 TC restricted the replication of genes related to carbon metabolism, the electron transport system and denitrification. Moreover, discrepant inhibitory effects of TC on individual denitrification steps, which led to the accumulation of nitrite, were observed in this study. These results provide the information that is necessary for evaluating the potential environmental risk of antibiotics on groundwater denitrification and bring more attention to their effects on geochemical nitrogen cycles.

Mechanistic insights into the response of electroactive biofilms to Cd2+ shock: bacterial viability and electron transfer behavior at the cellular and community levels

Electroactive biofilms (EABs) play a crucial role in environmental bioremediation due to their excellent extracellular electron transfer (EET) capabilities. However, Cd2+ can have toxic effects on the electrochemical performance of EABs, and the comprehensive inhibition mechanism of EABs in response to Cd2+ shock remains elusive. This study indicated that Cd2+ shock significantly reduced biomass and increased oxidative stress in EABs at the cellular level. The bacterial viability of EABs in phase III under 0.5 mM Cd2+ shock (EABCd2+-III0.5) decreased by 16.31% compared to EABCK-III. Moreover, intracellular NADH, c-Cyts, and the abundance of electroactive species were essential indicators to evaluate EET behavior of EABs. In EABCd2+-III0.5, these indicators decreased by 26.32%, 33.40%, and 20.65%, respectively. Structural equation modeling analysis established quantitative correlations between core components and electrochemical activity at cellular and community levels. The correlation analysis revealed that the growth and electron transfer functions of EABs were predictive indicators for their electrochemical performance, with standardized path coefficients of 0.407 and 0.358, respectively. These findings enhance our understanding of EABs' response to Cd2+ shock and provide insights for improving their performance in heavy metal wastewater.

How β-Cyclodextrin-Functionalized Biochar Enhanced Biodenitrification in Low C/N Conditions via Regulating Substrate Metabolism and Electron Utilization

Biodenitrification plays a vital role in the remediation of nitrogen-contaminated water. However, influent with a low C/N ratio limits the efficiency of denitrification and causes the accumulation/emission of noxious intermediates. In this study, β-cyclodextrin-functionalized biochar (BC@β-CD) was synthesized and applied to promote the denitrification performance of Paracoccus denitrificans when the C/N was only 4, accompanied by increased nitrate reduction efficiency and lower nitrite accumulation and nitrous oxide emission. Transcriptomic and enzymatic activity analyses showed BC@β-CD enhanced glucose degradation by promoting the activities of glycolysis (EMP), the pentose phosphate pathway (PPP), and the tricarboxylic acid (TCA) cycle. Notably, BC@β-CD drove a great generation of electron donors by stimulating the TCA cycle, causing a greater supply of substrate metabolism to denitrification. Meanwhile, the promotional effect of BC@β-CD on oxidative phosphorylation accelerates electron transfer and ATP synthesis. Moreover, the presence of BC@β-CD increased the intracellular iron level, causing further improved electron utilization in denitrification. BC@β-CD helped to remove metabolites and induced positive feedback on the metabolism of P. denitrificans. Collectively, these effects elevated the glucose utilization for supporting denitrification from 36.37% to 51.19%. This study reveals the great potential of BC@β-CD for enhancing denitrification under low C/N conditions and illustrates a potential application approach for β-CD in wastewater bioremediation.

Formation of typical disinfection by-products (DBPs) during chlorination and chloramination of polymyxin B sulfate

Disinfection by-products (DBPs) formed in chlorination and chloramination are proved to be cytotoxic and genotoxic and arouse increasing attention. However, previous studies of DBP precursors mainly focused on free amino acids (AAs) and few papers evaluated DBPs' formation potential of combined AAs. This study demonstrated that typical carbonaceous (C-) DBPs, trihalomethanes (THMs) and typical nitrogenous (N-) DBPs, dichloroacetonitrile (DCAN), trichloroacetonitrile (TCAN) and trichloronitromethane (TCNM) could be formed during chlorination and chloramination of polymyxin B sulfate (PBS), a common polypeptide antibiotic working against Gram-negative bacterial infections. The effects of major parameters, including disinfectant dose, contact time, solution pH, temperature, bromide concentration and chloramination mode were evaluated in batch experiments. Different kinds of DBPs exhibited different characteristics as disinfectant dose or contact time increased. Solution pH and temperature affected the formation of DBPs greatly. The formation pathways of different DBPs from chlor(am)ination of PBS were also proposed. Combined AAs, such as PBS, were proved to be important precursors of DBPs during disinfections.

Sulfamethoxazole impact on pollutant removal and microbial community of aerobic granular sludge with filamentous bacteria

In this study, sulfamethoxazole (SMX) was employed to investigate its impact on the process of aerobic granule sludge with filamentous bacteria (FAGS). FAGS has shown great tolerance ability. FAGS in a continuous flow reactor (CFR) could keep stable with 2 μg/L of SMX addition during long-term operation. The NH₄⁺, chemical oxygen demand (COD), and SMX removal efficiencies kept higher than 80%, 85%, and 80%, respectively. Both adsorption and biodegradation play important roles in SMX removal for FAGS. The extracellular polymeric substances (EPS) might play important role in SMX removal and FAGS tolerance to SMX. The EPS content increased from 157.84 mg/g VSS to 328.22 mg/g VSS with SMX addition. SMX has slightly affected on microorganism community. A high abundance of Rhodobacter, Gemmobacter, and Sphaerotilus of FAGS may positively correlate to SMX. The SMX addition has led to the increase in the abundance of the four sulfonamide resistance genes in FAGS.

Aerobic composting with sauerkraut fermentation waste water: Increasing the stability and complexity of bacterial community and changing bacterial community assembly processes

Aerobic composting renders the sauerkraut fermentation waste water harmless while adding soluble nutrients. Unravelling the bacterial community assembly processes, changes in community robustness and community cohesion and the relationship between them under composting treatment of sauerkraut fermentation waste water is an interesting topic. Sauerkraut fermentation waste water was used for composting, which increased bacterial linkages, community robustness, competitive behaviour during warming periods and cooperative behaviour during cooling periods, and the control of community assembly processes shifts from deterministic processes (variable selection) to stochastic processes (decentralised limitation). At the same time, the influence of community robustness and community cohesion on community assembly processes was increased. Community cohesion and robustness were significantly correlated with community function. These results indicate that community robustness and community cohesion are critical for the biological handling of hazardous substances.

Existence of antibiotic pollutant in agricultural soil: Exploring the correlation between microbiome and pea yield

Due to sewage irrigation, manure fertilizer application or other agricultural activities, antibiotics have been introduced into farmland as an emerging contaminant, existing with other agrochemicals. However, the potential influences of antibiotics on the efficiency of agrochemicals and crops health are still unclear. In this work, the effect of antibiotics on fertilization efficiency and pea yield was evaluated, and the mechanism was explored in view of soil microbiome. Nitrogen utilization and pea yield were decreased by antibiotics. In specific, the weight of seeds decreased 9.5 % by 5 mg/kg antibiotics and decreased 25.1 % by 50 mg/kg antibiotics. For N nutrient in pea, antibiotics resulted in 62.5 %-63.7 % decrease in amino acid content and 8.3 %-35.3 % decrease in inorganic-N content. Further research showed that antibiotics interfered with N cycle in soil, inhibiting urea decomposition and denitrification process by reducing function genes ureC, nirK and norB in soil, thus decreasing N availability. Meanwhile, antibiotics destroyed the enzyme function in N assimilation. This work evaluated the environmental risk of antibiotics from fertilization efficiency and N utilization in crop. Antibiotics could not only affect N cycle, limiting the decomposition of N fertilizer, but also affect N utilization in plants, thus affecting the yield and even the quality of leguminous crops.

Dipeptide-polysaccharides hydrogels through co-assembly

Self-assembling dipeptide hydrogels are attracting attention in food, materials, and biomedicine. However, there are still limitations such as weak hydrogel properties. Herein, we introduced two types of polysaccharides (Arabic gum and citrus pectin) into an alkyl-chain modified dipeptide (C₁₃-tryptophan-tyrosine (C₁₃-WY)) to generate co-assembled C₁₃-WY-arabic gum and C₁₃-WY-pectin hydrogels. The co-assembled hydrogels exhibited enhanced mechanical properties and stability. The G' value of C₁₃-WY-arabic gum and C₁₃-WY-pectin hydrogels was 3 and 10 times larger than that of C₁₃-WY hydrogel, respectively. The addition of Arabic gum and citrus pectin led to the co-assembly and molecular rearrangement. Moreover, co-assembled hydrogels showed more β-sheet structure and hydrogen bonds. Importantly, the self-/co-assembled hydrogels showed low cytotoxicity. We utilized these hydrogels for the encapsulation of docetaxel and they showed a high embedding rate and slow-release. Our findings provide a novel strategy for the development of stable supramolecular peptide hydrogels with good biocompatibility through simple co-assembly.

Insight into sulfamethoxazole effects on aerobic denitrification by strain Pseudomonas aeruginosa PCN-2: From simultaneous degradation performance to transcriptome analysis

It is a well-established fact that aerobic denitrifying strains are profoundly affected by antibiotics, but bacterium performing simultaneous aerobic denitrification and antibiotic degradation is hardly reported. Here, a typical aerobic denitrifying bacterium Pseudomonas aeruginosa PCN-2 was discovered to be capable of sulfamethoxazole (SMX) degradation. The results showed that nitrate removal efficiency was decreased from 100% to 88.12%, but the resistance of strain PCN-2 to SMX stress was enhanced with the increment of SMX concentration from 0 to 100 mg/L. Transcriptome analysis revealed that the down-regulation of energy metabolism pathways rather than the denitrifying functional genes was responsible for the suppressed nitrogen removal, while the up-regulation of antibiotic resistance pathways (e.g., biofilm formation, multi-drug efflux system, and quorum sensing) ensured the survival of bacterium and the carrying out of aerobic denitrification. Intriguingly, strain PCN-2 could degrade SMX during aerobic denitrification. Seven metabolites were identified by the UHPLC-MS, and three degradation pathways (which includes a new pathway that has never been reported) was proposed combined with the expressions of drug metabolic genes (e.g., cytP450, FMN, ALDH and NAT). This work provides a mechanistic understanding of the metabolic adaption of strain PCN-2 under SMX stress, which provided a broader idea for the treatment of SMX-containing wastewater.

A mechanistic review on aerobic denitrification for nitrogen removal in water treatment

The traditional biological nitrogen removal technology consists of two steps: nitrification by autotrophs in aerobic circumstances and denitrification by heterotrophs in anaerobic situations; however, this technology requires a huge area and stringent environmental conditions. Researchers reached the conclusion that the denitrification process could also be carried out in aerobic circumstances with the discovery of aerobic denitrification. The aerobic denitrification process is carried out by aerobic denitrifying bacteria (ADB), most of which are heterotrophic bacteria that can metabolize various forms of nitrogen compounds under aerobic conditions and directly convert ammonia nitrogen to N₂ for discharge from the system. Despite the fact that there is no universal agreement on the mechanism of aerobic denitrification, this article reviewed four current explanations for the denitrification mechanism of ADB, including the microenvironment theory, theory of enzyme, electron transport bottlenecks theory, and omics study, and summarized the parameters affecting the denitrification efficiency of ADB in terms of carbon source, temperature, dissolved oxygen (DO), and pH. It also discussed the current status of the application of aerobic denitrification in practical processes. Following the review, the difficulties of present aerobic denitrification technology are outlined and future research options are highlighted. This review may help to improve the design of current wastewater treatment facilities by utilizing ADB for effective nitrogen removal and provide the engineers with relevant references.

Nitrogen removal characteristics of efficient heterotrophic nitrification-aerobic denitrification bacterium and application in biological deodorization

A heterotrophic nitrifying aerobic denitrifying (HN-AD) strain HY-1 with excellent capacity, identified as Paracoccus denitrificans, was isolated from activated sludge. HY-1 was capable of removing NH₄⁺, NO₂^-, and NO₃^- with the corresponding rate of 17.33 mg-N L^-1 h^-1, 21.83 mg-N L^-1 h^-1, and 32.37 mg-N L^-1 h^-1, as well as the mixture of multiple nitrogen sources. Meanwhile, HY-1 could execute denitrification function under anaerobic conditions with a rate of 14.56 mg-N L^-1 h^-1. HY-1 required less energy investment, which exhibited average denitrification rate of 5.19 mg-N L^-1 h^-1 at carbon-nitrogen ratio was 1. After nitrification-denitrification metabolic pathway analysis, HY-1 was applied in a biological trickling filter reactor for compost deodorization. The results showed that adding of HY-1 greatly reduced the ionic concentration of NH₄⁺ and NO₃^- in the circulating liquid without impairing the deodorization effect (NH₃ removal rate＞98.07%). These findings extend the field of application of HN-AD and provide new insights for biological deodorization.

Co-culturing fungus Penicillium citrinum and strain Citrobacter freundii improved nitrate removal and carbon utilization by promoting glyceride metabolism

Exploring the interaction between denitrifying microbial species is significant for improving denitrification performance. In this study, the effects of co-culturing fungus Penicillium citrinum and strain Citrobacter freundii on denitrification were investigated. Results showed that the maximum nitrate removal and carbon utilization in co-culture were 68.0 and 14.1 mg·L^-1·d^-1, respectively. The total adenosine triphosphatase activity was increased to 9.87 U‧mg^-1 protein in co-culture, and nicotinamide adenine dinucleotide production was 1.7-2.3 times that of monoculture, attributing to increased carbon utilization. Further metabolomics and membrane permeability assay revealed that co-culture increased the metabolism of glycerides, thereby enhancing the membrane permeability of strain Citrobacter freundii and promoting the transmembrane transport of nitrate and glucose, which boosted nitrate reductase activity and nicotinamide adenine dinucleotide production in turn. In summary, co-culturing promoted carbon utilization and enhanced substrate removal efficiency through the metabolism of glycerides, which provided a strategy to enhance denitrification performance in wastewater treatment.

Overexpression of pdeR promotes biofilm formation of Paracoccus denitrificans by promoting ATP production and iron acquisition

Bacterial biofilms are ubiquitous in natural environments and play an essential role in bacteria’s environmental adaptability. Quorum sensing (QS), as the main signaling mechanism bacteria used for cell-to-cell communication, plays a key role in bacterial biofilm formation. However, little is known about the role of QS circuit in the N-transformation type strain, Paracoccus denitrificans, especially for the regulatory protein PdeR. In this study, we found the overexpression of pdeR promoted bacterial aggregation and biofilm formation. Through RNA-seq analysis, we demonstrated that PdeR is a global regulator which could regulate 656 genes expression, involved in multiple metabolic pathways. Combined with transcriptome as well as biochemical experiments, we found the overexpressed pdeR mainly promoted the intracellular degradation of amino acids and fatty acids, as well as siderophore biosynthesis and transportation, thus providing cells enough energy and iron for biofilm development. These results revealed the underlying mechanism for PdeR in biofilm formation of P. denitrificans, adding to our understanding of QS regulation in biofilm development.