N2O recovery from wastewater and flue gas via microbial denitrification: Processes and mechanisms.

Nitrous oxide (N2O) is increasingly regarded as a significant greenhouse gas implicated in global warming and the depletion of the ozone layer, yet it is also recognized as a valuable resource. This paper comprehensively reviews innovative microbial denitrification techniques for recovering N2O from nitrogenous wastewater and flue gas. Critical analysis is carried out on cutting-edge processes such as the coupled aerobic-anoxic nitrous decomposition operation (CANDO) process, semi-artificial photosynthesis, and the selective utilization of microbial strains, as well as flue gas absorption coupled with heterotrophic/autotrophic denitrification. These processes are highlighted for their potential to facilitate denitrification and enhance the recovery rate of N2O. The review integrates feasible methods for process control and optimization, and presents the underlying mechanisms for N2O recovery through denitrification, primarily achieved by suppressing nitrous oxide reductase (Nos) activity and intensifying competition for electron donors. The paper concludes by recognizing the shortcomings in existing technologies and proposing future research directions, with an emphasis on prioritizing the collection and utilization of N2O while considering environmental sustainability and economic feasibility. Through this review, we aim to inspire interest in the recovery and utilization of N2O, as well as the development and application of related technologies.

Disinfectant polyhexamethylene guanidine triggered simultaneous efflux pump antibiotic- and metal-resistance genes propagation during sludge anaerobic digestion.

The environmental transmission of antibiotic resistance genes (ARGs) and metal resistance genes (MRGs) exerted devastating threats to global public health, and their interactions with other emerging contaminants (ECs) have raised increasing concern. This study investigated that the abundances of ARGs and MRGs with the predominant type of efflux pump were simultaneously increased (8.4-59.1%) by disinfectant polyhexamethylene guanidine (PHMG) during waste activated sludge (WAS) anaerobic digestion. The aggregation of the same microorganisms (i.e., Hymenobacter and Comamonas) and different host bacteria (i.e., Azoarcus and Thauera) were occurred upon exposure to PHMG, thereby increasing the co-selection and propagation of MRGs and ARGs by vertical gene transfer. Moreover, PHMG enhanced the process of horizontal gene transfer (HGT), facilitating their co-transmission by the same mobile genetic elements (20.2-223.7%). Additionally, PHMG up-regulated the expression of critical genes (i.e., glnB, trpG and gspM) associated with the HGT of ARGs and MRGs (i.e., two-component regulatory system and quorum sensing) and exocytosis system (i.e., bacterial secretion system). Structural equation model analysis further verified that the key driver for the simultaneous enrichment of ARGs and MRGs under PHMG stress was microbial community structure. The study gives new insights into the aggravated environmental risks and mechanisms of ECs in sludge digestion system, providing guidance for subsequent regulation and control of ECs.

A plant NLR receptor employs ABA central regulator PP2C-SnRK2 to activate antiviral immunity.

Defence against pathogens relies on intracellular nucleotide-binding, leucine-rich repeat immune receptors (NLRs) in plants. Hormone signaling including abscisic acid (ABA) pathways are activated by NLRs and play pivotal roles in defence against different pathogens. However, little is known about how hormone signaling pathways are activated by plant immune receptors. Here, we report that a plant NLR Sw-5b mimics the behavior of the ABA receptor and directly employs the ABA central regulator PP2C-SnRK2 complex to activate an ABA-dependent defence against viral pathogens. PP2C4 interacts with and constitutively inhibits SnRK2.3/2.4. Behaving in a similar manner as the ABA receptor, pathogen effector ligand recognition triggers the conformational change of Sw-5b NLR that enables binding to PP2C4 via the NB domain. This receptor-PP2C4 binding interferes with the interaction between PP2C4 and SnRK2.3/2.4, thereby releasing SnRK2.3/2.4 from PP2C4 inhibition to activate an ABA-specific antiviral immunity. These findings provide important insights into the activation of hormone signaling pathways by plant immune receptors.

EV-COMM: A database of interspecies and intercellular interactions mediated by extracellular vesicles.

Intra- and inter-organismal interactions play a crucial role in the maintenance and function of individuals, as well as communities. Extracellular vesicles (EVs) have been identified as effective mediators for the communication both within and between species. They can carry and transport molecular cargoes to transmit biological messages. Several databases (ExoBCD, ExoCarta, EVpedia, EV-TRACK, Vesiclepedia) complied the cargoes information including DNA, RNA, protein, lipid and metabolite associated with EVs. Databases that refer to the complete records on both donor and recipient information are warranted to facilitate the understanding of the interaction across cells and species. In this study, we developed a database that compiled the records equipped with a structured process of EV-mediated interaction. The sources of donor and recipient were classified by cell type, tissues/organs and species, thus providing an extended knowledge of cell-cell, species-species interaction. The isolation and identification methods were presented for assessing the quality of EVs. Information on functional cargoes was included, where microRNA was linked to a prediction server to broaden its potential effects. Physiological and pathological context was marked to show the environment where EVs functioned. At present, a total of 1481 data records in our database, including 971 cell-cell interactions belonging to more than 40 different tissues/organs, and 510 cross-species records. The database provides a web interface to browse, search, visualize and download the interaction records. Users can search for interactions by selecting the context of interest or specific cells/species types, as well as functional cargoes. To the best of our knowledge, the database is the first comprehensive database focusing on interactions between donor and recipient cells or species mediated by EVs, serving as a convenient tool to explore and validate interactions. The Database, shorten as EV-COMM (EV mediated communication) is freely available at http://sdc.iue.ac.cn/evs/list/ and will be continuously updated.

Efficient nitrate and Cr(VI) removal by denitrifier: The mechanism of S. oneidensis MR-1 promoting electron production, transportation and consumption.

When Cr(VI) and nitrate coexist, the efficiency of both bio-denitrification and Cr(VI) bio-reduction is poor because chromate hinders bacterial normal functions (i.e., electron production, transportation and consumption). Moreover, under anaerobic condition, the method about efficient nitrate and Cr(VI) removal remained unclear. In this paper, the addition of Shewanella oneidensis MR-1 to promote the electron production, transportation and consumption of denitrifier and cause an increase in the removal of nitrate and Cr(VI). The efficiency of nitrate and Cr(VI) removal accomplished by P. denitrificans as a used model denitrifier increased respectively from 51.3% to 96.1% and 34.3% to 99.8% after S. oneidensis MR-1 addition. The mechanism investigations revealed that P. denitrificans provided S. oneidensis MR-1 with lactate, which was utilized to secreted riboflavin and phenazine by S. oneidensis MR-1. The riboflavin served as coenzymes of cellular reductants (i.e., thioredoxin and glutathione) in P. denitrificans, which created favorable intracellular microenvironment conditions for electron generation. Meanwhile, phenazine promoted biofilm formation, which increased the adsorption of Cr(VI) on the cell surface and accelerated the Cr(VI) reduction by membrane bound chromate reductases thereby reducing damage to other enzymes respectively. Overall, this strategy reduced the negative effect of chromate, thus improved the generation, transportation, and consumption of electrons. SYNOPSIS: The presence of S. oneidensis MR-1 facilitated nitrate and Cr(VI) removal by P. denitrificans through decreasing the negative effect of chromate due to the metabolites' secretion.

Antibiotics and antibiotic-associated diarrhea: a real-world disproportionality study of the FDA adverse event reporting system from 2004 to 2022.

BACKGROUND: Our study aimed to assess the risk signals of antibiotic-associated diarrhea (AAD) caused by various antibiotics using real-world data and provide references for safe clinical applications. METHODS: We analyzed data extracted from the FDA Adverse Event Reporting System (FAERS) database, covering the period from the first quarter of 2004 to the third quarter of 2022. We computed the reporting odds ratio (ROR) for each antibiotic or antibiotic class to compare the signal difference. Furthermore, we also examined the differences in the onset times and outcomes of AAD caused by various antibiotics. RESULTS: A total of 5,397 reports met the inclusion requirements. Almost all antibiotics, except tobramycin and minocycline (ROR 0.98; 95%CI: 0.64-1.51 and 0.42; 95%CI: 0.16-1.11, respectively), showed a significant correlation with AAD. The analysis of the correlation between different classes of antibiotics and AAD revealed that lincomycins (ROR 29.19; 95%CI: 27.06-31.50), third-generation cephalosporins (ROR 15.96; 95%CI: 14.58-17.47), and first/second generation cephalosporins (ROR 15.29; 95%CI: 13.74-17.01) ranked the top three. The ROR values for antibiotics from the same class of antibiotics also varied greatly, with the ROR values for third-generation cephalosporins ranging from 9.97 to 58.59. There were also differences in ROR values between ß-lactamase inhibitors and their corresponding ß-lactamase drugs, such as amoxicillin-clavulanate (ROR = 13.31; 95%CI: 12.09-14.65) and amoxicillin (ROR = 6.50; 95%CI: 5.69-7.44). 91.35% of antibiotics have an onset time of less than four weeks. CONCLUSIONS: There is a significant correlation between almost all antibiotics and AAD, particularly lincomycins and ß-lactam antibiotics, as well as a different correlation within the same class. These findings offer valuable evidence for selecting antibiotics appropriately.

High-order time lacunarity feature-aided multiple hypotheses tracking for underwater active small targets in high-clutter harbor environment.

Active tracking of underwater small targets is a great challenge with kinematic information alone. This is because the active sonar often encounters multipath propagation and the induced clutter can even mask target echoes. Recently, high-order time lacunarity (HOT-Lac) has shown its ability in effectively highlighting "blob" targets from high clutter harbor environments. Hence, this paper proposes a HOT-Lac aided track scoring mechanism to solve the ambiguity of data association within the framework of Multiple Hypotheses Tracking (MHT). Specifically, the trajectory consistency of potential targets is captured by a momentum accumulation of the HOT Lac feature, which can inherit the historical information for the whole track. Meanwhile, due to the separability of the distribution of target and clutter in the HOT-Lac feature space, the probabilities of the target hypothesis and null hypothesis are modeled by the online computation of the HOT-Lac feature. Finally, the cumulative likelihood ratio based on HOT-Lac is integrated into MHT to score the potential tracks. Experiments in several real-world harbor scenarios demonstrate that the proposed HOT-Lac feature-aided tracker can suppress false tracks accurately and quickly.

Metabolite Cross-Feeding Promoting NADH Production and Electron Transfer during Efficient SMX Biodegradation by a Denitrifier and S. oneidensis MR-1 in the Presence of Nitrate.

Antibiotics often coexist with other pollutants (e.g., nitrate) in an aquatic environment, and their simultaneous biological removal has attracted widespread interest. We have found that sulfamethoxazole (SMX) and nitrate can be efficiently removed by the coculture of a model denitrifier (Paracoccus denitrificans, Pd) and Shewanella oneidensis MR-1 (So), and SMX degradation is affected by NADH production and electron transfer. In this paper, the mechanism of a coculture promoting NADH production and electron transfer was investigated by proteomic analysis and intermediate experiments. The results showed that glutamine and lactate produced by Pd were captured by So to synthesize thiamine and heme, and the released thiamine was taken up by Pd as a cofactor of pyruvate and ketoglutarate dehydrogenase, which were related to NADH generation. Additionally, Pd acquired heme, which facilitated electron transfer as heme, was the important composition of complex III and cytochrome c and the iron source of iron sulfur clusters, the key component of complex I in the electron transfer chain. Further investigation revealed that lactate and glutamine generated by Pd prompted So chemotactic moving toward Pd, which helped the two bacteria effectively obtain their required substances. Obviously, metabolite cross-feeding promoted NADH production and electron transfer, resulting in efficient SMX biodegradation by Pd and So in the presence of nitrate. Its feasibility was finally verified by the coculture of an activated sludge denitrifier and So.

Papillary thyroid carcinoma with desmoid-type fibromatosis: the clinicopathological features with characteristic imaging and molecular correlation requiring comprehensive treatment.

The pathogenesis and treatment of papillary thyroid cancer with desmoid-type fibromatosis (PTC-DTF), a rare subtype of papillary thyroid carcinoma characterized by a mixed epithelial-mesenchymal structure, are still ill-defined. Previous reports on PTC-DTF have had limited follow-up and recurrence has been rarely reported. To better understand this condition, we conducted a thorough analysis of five cases of PTC-DTF from our institute, including clinical and pathological examinations, imaging, immunohistochemistry, and molecular analysis. We also reviewed relevant literature. The mean age of the patients was 51.8 years, with three women and two men included in the group. Ultrasound often showed a hypoechogenic and well-defined nodule in the thyroid gland, except for one individual who had distant lung metastases detected by PET-CT. The nodules ranged in width from 0.5 to 5.0 cm and were excised in each case. Following surgery, 131I therapy was used in two cases. The overall number of PTC-DTF cases has risen from the previously reported 55 to 60, with females being the most commonly affected and ranging in age from 19 to 82. Most masses underwent a thyroidectomy, and approximately half of the patients had lymph node metastases. Histologically, PTC-DTFs were composed of a predominant stromal component (65%-90%) and an intervening epithelial component. These spindle cells were arranged in parallel with abundant cytoplasm and vacuole-like nucleus but there wasn't evident atypia. The carcinoma cells were positively stained for CK and TTF-1 by immunohistochemistry, whereas mesenchymal cells were positive for SMA and displayed nuclear immunoreactivity for ß-catenin. BRAF, NRAS, and CTNNB1 mutations were identified in the epithelial and mesenchymal components through molecular testing, respectively. Perhaps because the mesenchyme harbors aberrant nuclear ß-catenin expression, PTC-DTF is more aggressive and prone to invasion and distant recurrence, as shown by our case 2, which is the first case to be reported thus far. PTC-DTF is typically treated with surgery, but clinicians may occasionally consider more holistic treatment plans that involve radioactive iodine and endocrine therapy.

Surfactant aggravated the antibiotic's stress on antibiotic resistance genes proliferation by altering antibiotic solubilization and microbial traits in sludge anaerobic fermentation.

The excessive application of antibiotics and surfactants resulted in their massive accumulation in waste activated sludge (WAS), but the co-occurrent impacts of antibiotics and surfactants on the antibiotic resistant genes (ARGs) fates have seldom reported. This work mainly revealed the roles and critical mechanisms of sodium dodecyl benzene sulfonate (SDBS) on the sulfadiazine (SDZ) stressing for ARGs distribution during WAS anaerobic fermentation. High-throughput qPCR and metagenomic analysis revealed that SDBS aggravated the SDZ selective pressure, and accelerated the proliferation of ARGs. The total abundance of ARGs was increased from 8.81 × 1010 in SDZ to 1.17 × 1011 copies/g TSS in the SDBS/SDZ co-occurrence system. Specifically, the absolute abundances of ermF (MLSB), mefA (MLSB), tetM-01 (tetracycline), tetX (tetracycline), sul2 (sulfonamide) and strB (aminoglycoside) were risen from 4.60 × 108-7.44 × 109 copies/g TSS in the SDZ reactor to 1.02 × 109-4.63 × 1010 copies/g TSS in SDBS/SDZ reactor. SDBS was contributed to the SDZ solubilization and simultaneously effective in disintegrating extracellular polymeric substances and improving cell membrane permeability, which would facilitate the SDZ transport and its interactions with ARGs hosts. Consequently, the microbial community structure was evidently altered, and the typical ARGs hosts (i.e., Saccharimonadales and Ahniella) were greatly enriched. Also, the cell signal transduction systems (i.e., glnL, glrK and pilG), oxidative stress response (i.e., frmA and recA) and bacterial secretion systems (i.e., VirB4), which were related with ARGs propagation, were all provoked in the co-occurred SDBS/SDZ reactor compared with that of sole SDZ. PLS-PM analysis suggested that the bacterial community was the predominant factor that determined the ARGs fates, followed by mobile genetic elements and metabolic pathway. This work demonstrated the interactive effects of surfactants and antibiotics on the ARGs fates in WAS fermentation systems and gave insightful implications on the ecological risks of different exogenous pollutants.

Long-term exposure to zinc oxide nanoparticles improves PAOs function in enhanced biological phosphorus removal.

As the most widely applied process for biological phosphorus removal, enhanced biological phosphorus removal (EBPR) relies on phosphorus accumulating organisms (PAOs) and glycogen accumulating organisms (GAOs), whose function is crucial for the removal of phosphorus. In this study, the effect of zinc oxide nanoparticles (ZnO NPs, 0-50 mg/L) on EBPR performance was investigated in both long-term reactors and batch experiments. It was found that the performance of biological phosphorus removal was recovered from 0% (day 0) to >99% (day 70) after long-term exposure of ZnO NPs (50 mg/L). Further studies revealed that ZnO NPs treatment caused no significant effects on the morphology and settleability of activated sludge, but enhanced the release and uptake of phosphorus as well as the transformations of polyhydroxyalkanoates and glycogen in activated sludge, which suggested that PAOs were re-activated during long-term exposure to ZnO NPs. Fluorescence in-situ hybridization (FISH) analysis showed that the relative abundance of PAOs was increased after long-term exposure. Meanwhile, the enzymatic activities of PPX and PPK were also enhanced. These results indicated that compared with short-term exposure, long-term exposure to ZnO NPs favours PAOs function and thus led to the recovery of biological phosphorus removal.

Contamination, sources and health risks of potentially toxic elements in the coastal multimedia environment of South China.

Coastal ecosystems are vulnerable to the accumulation of potentially toxic elements (PTEs), which pose a threat to marine ecosystems and human health. In this study, the concentrations of eight PTEs in a typical area of South China were analysed, and their distributions, seasonal variations, pollution degrees, potential health risks and sources in seawater, sediment and organisms were evaluated. The comprehensive pollution index (CPI), pollution load index (PLI), potential ecological risk index (PERI) and target hazard quotient (THQ) were applied to assess seawater, sediment and organism quality, respectively. The annual mean concentrations of Zn, Hg, Cr and As in the bottom seawater were higher than those in the surface water while those of Pb, Mn and Cu were higher in the surface seawater. The mean content of Hg was higher than the corresponding background value of that in China Shelf Sea sediment. Marine organisms have a high enrichment capacity for Cu, Zn, Cr, Hg, As and Mn in seawater. Based on CPI, the seawater was generally not polluted by PTEs. The PLI and PERI results demonstrated that Hg was the main contamination element in surface sediment. The total target hazard quotient (TTHQ) analysis illustrated that long-term consumption of some fish by children poses a noncarcinogenic health risk, while that risk to adults is negligible. Natural sources, agricultural activity sources, coal burning and industrial emission sources were the main sources of the PTEs in surface sediments according to positive matrix factorization (PMF) model.

Diverse functional genes harboured in extracellular vesicles from environmental and human microbiota.

Exchange of mobile functional genes within microbiota benefits the microbial community. However, the status of the mobile gene pool in environment is still largely unclear, impeding the understanding on the process of gene transfer in natural microbial communities. The release of extracellular vesicles (EVs) by diverse organisms has been proposed to be a vital way in the complex networks of interactions between microbes and their habitats. In this study, we hypothesized that microbial EVs encapsulating functional DNA are widely distributed in the environmental matrix. The prevalence, source and DNA cargoes of EVs in three types of typical microbial habitats were studied. High abundance of EVs comparable to the bacterial concentration was found in human faeces, wastewater and soil. Metagenomic analysis showed the diverse and differential taxonomy of EVs-associated DNA compared to source microbiome. An array of efficient EVs producing species was identified. A wide variety of mobile genes including glycoside hydrolase family 25 were enriched. Antibiotic resistance genes co-localizing with mobile genetic elements were abundant in the EVs. This study provides novel insights into the prevalent EVs as a reservoir for the mobile functional genes in the natural environment.

Reductive Stress Boosts the Horizontal Transfer of Plasmid-Borne Antibiotic Resistance Genes: The Neglected Side of the Intracellular Redox Spectrum.

The dissemination of plasmid-borne antibiotic resistance genes (ARGs) among bacteria is becoming a global challenge to the "One Health" concept. During conjugation, the donor/recipient usually encounter diverse stresses induced by the surrounding environment. Previous studies mainly focused on the effects of oxidative stress on plasmid conjugation, but ignored the potential contribution of reductive stress (RS), the other side of the intracellular redox spectrum. Herein, we demonstrated for the first time that RS induced by dithiothreitol could significantly boost the horizontal transfer of plasmid RP4 from Escherichia coli K12 to different recipients (E. coli HB101, Salmonella Typhimurium, and Pseudomonas putida KT2440). Phenotypic and genotypic tests confirmed that RS upregulated genes encoding the transfer apparatus of plasmid RP4, which was attributed to the promoted consumption of intracellular glutamine in the donor rather than the widely reported SOS response. Moreover, RS was verified to benefit ATP supply by activating glycolysis (e.g., GAPDH) and the respiratory chain (e.g., appBC), triggering the deficiency of intracellular free Mg2+ by promoting its binding, and reducing membrane permeability by stimulating cardiolipin biosynthesis, all of which were beneficial to the functioning of transfer apparatus. Overall, our findings uncovered the neglected risks of RS in ARG spreading and updated the regulatory mechanism of plasmid conjugation.

Motion compensation using joint-sub-band phase unwrapping for synthetic aperture sonar.

Displaced phase center antenna (DPCA) micro-navigation has been widely applied in the motion compensation of synthetic aperture sonars (SASs). Estimating the time delay is the most important step for DPCA-based motion compensation. However, at present, the existing methods of estimating the time delay in motion compensation are not sufficiently accurate, which limits the improvement of imaging quality of SASs. This paper proposes a time delay estimation method using joint-sub-band phase unwrapping, which achieves much higher estimation accuracy than the reference method. The experimental results demonstrate that the proposed method dramatically improves the SAS imaging quality, compared to the reference method.

[Mechanism of the inhibitory effects of thalidomide on expressions of VEGF and bFGF].

Objective: To investigate the inhibitory effects of thalidomide on the expressions of VEGF and bFGF in human lung adenocarcinoma A549 cells and human hepatocellular carcinomas HepG2 cells mediated by cereblon (CRBN). Methods: shRNA technology was used to construct the A549 cell line (A549CRBN) and HepG2 cell line (HepG2CRBN) with stable knockdown of CRBN, which was verified by real-time PCR and Western blot. A549 cells were divided into negative control group (A549luciferase) and CRBN down-regulation group (A549CRBN); HepG2 cells were divided into negative control group (HepG2luciferase) and CRBN down-regulation group (HepG2CRBN). The above cells were seeded into 6-well plates at 3×105 cells/well, and cultured in a 37℃, 5% CO2 incubator for 24 h. Then, 1 ml medium containing 100 µmol/L thalidomide (thalidomide group) and 1 ml medium containing 1‰ DMSO (control group) were added respectively, and the culture was continued for 24 hours before subsequent experiments. Each group was designed with three replicate wells. The effect of thalidomide on the activity of A549 cell line was detected by MTS assay. Real-time PCR was performed to detect mRNA expression levels of VEGF, bFGF and c-jun. ELISA assay was performed to detect protein expressions of VEGF and bFGF. Results: Compared with the control group, thalidomide at the concentrations of 1, 10, 50 and 100 µmol/L had no significant effects on the proliferation of A549 and HepG2 cells (P＞0.05). VEGF and bFGF levels in the A549CRBN or HepG2luciferase groups were significantly lower than those in the A549CRBN or HepG2CRBN groups (P＜0.05). Compared with the control group of the A549luciferase or HepG2luciferase, thalidomide inhibited the expressions of VEGF and bFGF in A549luciferase and HepG2luciferase cells (P＜ 0.05), but did not inhibit the expressions of VEGF and bFGF in A549CRBN and HepG2CRBN cells. Compared with the control group of the HepG2luciferase, thalidomide inhibited c-Jun expression in HepG2luciferase cells (P＜0.01), but did not significantly inhibit c-Jun expression in HepG2CRBN cells. Conclusion: The inhibitory effects of thalidomide on VEGF and bFGF expressions may be mediated by CRBN in A549 and HepG2 cells, and c-Jun may be one of the key transcription factors responsible for this inhibition.

Recent advances in biological removal of nitroaromatics from wastewater.

Various nitroaromatic compounds (NACs) released into the environment cause potential threats to humans and animals. Biological treatment is valued for cost-effectiveness, environmental friendliness, and availability when treating wastewater containing NACs. Considering the significance and wide use of NACs, this review focuses on recent advances in biological treatment systems for NACs removal from wastewater. Meanwhile, factors affecting biodegradation and methods to enhance removal efficiency of NACs are discussed. The selection of biological treatment system needs to consider NACs loading and cost, and its performance is affected by configuration and operation strategy. Generally, sequential anaerobic-aerobic biological treatment systems perform better in mineralizing NACs and removing co-pollutants. Future research on mechanism exploration of NACs biotransformation and performance optimization will facilitate the large-scale application of biological treatment systems.

Amino Acid Configuration Affects Volatile Fatty Acid Production during Proteinaceous Waste Valorization: Chemotaxis, Quorum Sensing, and Metabolism.

During proteinaceous waste valorization to produce volatile fatty acids (VFAs), protein needs to be hydrolyzed to amino acids (AAs), but the effects of the configuration of AAs on their biotransformation and VFA production have not been investigated. In this study, more residual d-AAs than their corresponding l-AAs were observed after VFAs were produced from kitchen waste in a pilot-scale bioreactor. For all AAs investigated, the VFA production from d-AAs was lower than that from corresponding l-AAs. The metagenomics and metaproteomics analyses revealed that the l-AA fermentation system exhibited greater bacterial chemotaxis and quorum sensing (QS) than d-AAs, which benefited the establishment of functional microorganisms (such as Clostridium, Sedimentibacter, and Peptoclostridium) and expression of functional proteins (e.g., substrate transportation cofactors, l-AA dehydrogenase, and acidogenic proteins). In addition, d-AAs need to be racemized to l-AAs before being metabolized, and the difference of VFA production between d-AAs and l-AAs decreased with the increase of racemization activity. The findings of the AA configuration affecting bacterial chemotaxis and QS, which altered microorganism communities and functional protein expression, provided a new insight into the reasons for higher l-AA metabolism than d-AAs and more d-AAs left during VFA production from proteinaceous wastes.

Nitric Oxide: A Neglected Driver for the Conjugative Transfer of Antibiotic Resistance Genes among Wastewater Microbiota.

The dissemination of plasmid-borne antibiotic resistance genes (ARGs) in wastewater is becoming an urgent concern. Previous studies mainly focused on the effects of coexisting contaminants on plasmid conjugation, but ignored the potential contribution of some byproducts inevitably released from wastewater treatment processes. Herein, we demonstrate for the first time that nitric oxide (NO), an intermediate of the wastewater nitrogen cycle, can significantly boost the conjugative transfer of plasmid RP4 from Escherichia coli K12 to different recipients (E. coli HB101, Salmonella typhimurium, and wastewater microbiota). Phenotypic and genotypic tests confirmed that NO-induced promotion was not attributed to the SOS response, a well-recognized driver for horizontal gene transfer. Instead, NO exposure increased the outer membrane permeability of both the donor and recipient by inhibiting the expression of key genes involved in lipopolysaccharide biosynthesis (such as waaJ), thereby lowering the membrane barrier for conjugation. On the other hand, NO exposure not only resulted in the accumulation of intracellular tryptophan but also triggered the deficiency of intracellular methionine, both of which were validated to play key roles in regulating the global regulatory genes (korA, korB, and trbA) of plasmid RP4, activating its encoding transfer apparatus (represented by trfAp and trbBp). Overall, our findings highlighted the risks of NO in spreading ARGs among wastewater microbiota and updated the regulation mechanism of plasmid conjugation.

Hydrogen-oxidizing bacteria and their applications in resource recovery and pollutant removal.

Hydrogen oxidizing bacteria (HOB), a type of chemoautotroph, are a group of bacteria from different genera that share the ability to oxidize H2 and fix CO2 to provide energy and synthesize cellular material. Recently, HOB have received growing attention due to their potential for CO2 capture and waste recovery. This review provides a comprehensive overview of the biological characteristics of HOB and their application in resource recovery and pollutant removal. Firstly, the enzymes, genes and corresponding regulation systems responsible for the key metabolic processes of HOB are discussed in detail. Then, the enrichment and cultivation methods including the coupled water splitting-biosynthetic system cultivation, mixed cultivation and two-stage cultivation strategies for HOB are summarized, which is the critical prerequisite for their application. On the basis, recent advances of HOB application in the recovery of high-value products and the removal of pollutants are presented. Finally, the key points for future investigation are proposed that more attention should be paid to the main limitations in the large-scale industrial application of HOB, including the mass transfer rate of the gases, the safety of the production processes and products, and the commercial value of the products.