Enhancement of antibiotic resistance dissemination by artificial sweetener acesulfame potassium: Insights from cell membrane, enzyme, energy supply and transcriptomics

The resistance change and stress response mechanisms of chlorine-resistant bacteria under microplastic stress in drinking water distribution system

The presence of both chlorine-resistant bacteria (CRB) and microplastics (MPs) in drinking water distribution systems (DWDS) poses a threat to water quality and human health. However, the risk of CRB bio evolution under the stress of MPs remains unclear. In this study, polypropylene (PP) and polyethylene (PE) were selected to study the adsorption and desorption behavior of sulfamethoxazole (SMX), and it was clear that MPs had the risk of carrying pollutants into DWDS and releasing them. The results of the antibiotic susceptibility test and disinfection experiment confirmed that MPs could enhance the resistance of CRB to antibiotics and disinfectants. Bacteria epigenetic resistance mechanisms were approached from multiple perspectives, including physiological and biochemical characteristics, as well as molecular regulatory networks. When MPs enter DWDS, CRB could attach to the surface of MPs and directly interact with both MPs and the antibiotics they release. This attachment process promoted changes in the composition and content of extracellular polymers (EPS) within cells, enhanced surface hydrophobicity, stimulated oxidative stress function, and notably elevated the relative abundance of certain antibiotic resistance genes (ARGs). This study elucidates the mechanism by which MPs alter the intrinsic properties of CRB, providing valuable insights into the effective avoidance of biological risks to water quality during CRB evolution.

Acesulfame and other artificial sweeteners in a wastewater treatment plant in Alberta, Canada: Occurrence, degradation, and emission

Acesulfame (ACE), sucralose (SUC), cyclamate (CYC), and saccharin (SAC) are widely used artificial sweeteners that undergo negligible metabolism in the human body, and thus ubiquitously exist in wastewater treatment plants (WWTPs). Due to their persistence in WWTPs, ACE and SUC are found in natural waters globally. Wastewater samples were collected from the primary influent, primary effluent, secondary effluent, and final effluent of a WWTP in Alberta, Canada between August 2022 and February 2023, and the artificial sweeteners concentrations were measured by LC-MS/MS. Using wastewater-based epidemiology, the daily per capita consumption of ACE in the studied wastewater treatment plant catchment was estimated to be the highest in the world. Similar to other studies, the removal efficiency in WWTP was high for SAC and CYC, but low or even negative for SUC. However, ACE removal remained surprisingly high (>96%), even in the cold Canadian winter months. This result may indicate a further adaptation of microorganisms capable of biodegrading ACE in WWTP. The estimated per capita discharge into the environment of ACE, CYC, and SAC is low in Alberta due to the prevalent utilization of secondary treatment throughout the province, but is 17.4-18.8 times higher in Canada, since only 70.3% of total discharged wastewater in Canada undergoes secondary treatment.

Acesulfame degradation by thermally activated persulfate: Kinetics, transformation products and estimated toxicity

The existence of the artificial sweetener acesulfame (ACE) in quantities of significance can negatively impact water quality, and its consumption has been associated with deleterious health effects. The present investigation explores the efficacy of heat-activated sodium persulfate (SPS) for eliminating ACE. The complete degradation of 0.50 mg L-1 of ACE was achieved within 45 min under a reaction temperature of 50 °C and 100 mg L-1 of SPS. The impact of thermal decomposition on ACE at a temperature of 60 °C was negligible. This study considers several factors, such as the SPS and ACE loading, the reaction temperature, the initial pH, and the water matrix of the reactor. The results indicate that the method's efficiency is positively correlated with higher initial concentrations of SPS, whereas it is inversely associated with the initial concentration of ACE. Furthermore, higher reaction temperatures and acidic initial pH levels promote the degradation of acesulfame. At the same time, certain constituents of the water matrix, such as humic acid, chlorides, and bicarbonates, can hinder the degradation process. Additionally, the data from LC-QToF-MS analysis of the samples were used to investigate transformation through suspect and non-target screening approaches. Overall, ACE's eight transformation products (TPs) were detected, and a potential ACE decomposition pathway was proposed. The concentration of TPs followed a volcano curve, decreasing in long treatment times. The ecotoxicity of ACE and its identified TPs was predicted using the ECOSAR software. The majority of TPs exhibited not harmful values.

Overcoming biological barriers by virus-like drug particles for drug delivery

Virus-like particles (VLPs) have natural structural antigens similar to those found in viruses, making them valuable in vaccine immunization. Furthermore, VLPs have demonstrated significant potential in drug delivery, and emerged as promising vectors for transporting chemical drug, genetic drug, peptide/protein, and even nanoparticle drug. With virus-like permeability and strong retention, they can effectively target specific organs, tissues or cells, facilitating efficient intracellular drug release. Further modifications allow VLPs to transfer across various physiological barriers, thus acting the purpose of efficient drug delivery and accurate therapy. This article provides an overview of VLPs, covering their structural classifications, deliverable drugs, potential physiological barriers in drug delivery, strategies for overcoming these barriers, and future prospects.

Artificial Sweetener Enhances the Spread of Antibiotic Resistance Genes During Anaerobic Digestion

Artificial sweeteners have been frequently detected in the feedstocks of anaerobic digestion. As these sweeteners can lead to the shift of anaerobic microbiota in the gut similar to that caused by antibiotics, we hypothesize that they may have an antibiotic-like impact on antibiotic resistance genes (ARGs) in anaerobic digestion. However, current understanding on this topic is scarce. This investigation aimed to examine the potential impact of acesulfame, a typical artificial sweetener, on ARGs in anaerobic digestion by using metagenomics sequencing and qPCR. It was found that acesulfame increased the number of detected ARG classes and the abundance of ARGs during anaerobic digestion. The abundance of typical mobile genetic elements (MGEs) and the number of potential hosts of ARGs also increased under acesulfame exposure, suggesting the enhanced potential of horizontal gene transfer of ARGs, which was further confirmed by the correlation analysis between absolute abundances of the targeted ARGs and MGEs. The increased horizontal dissemination of ARGs may be associated with the SOS response induced by the increased ROS production, and the increased cellular membrane permeability. These findings indicate that artificial sweeteners may accelerate ARG spread through digestate disposal, thus corresponding strategies should be considered to prevent potential risks in practice.

Effect of resistance difference on distribution of antibiotics in bacterial cell and conjugative gene transfer risks during electrochemical flow through reaction

The occurrences and spread of antibiotic resistance (AR) mediated by horizontal gene transfer (HGT) of antibiotic resistance genes (ARGs) in aquatic environment have been aggravated because of the abuse of antibiotics. While the pressure of different antibiotics is known to induce the spread of AR in bacteria, whether distribution of different antibiotics in cell structure could affect HGT risks is not clear. Here, a significant difference between the distribution of tetracycline hydrochloride (Tet) and sulfamethoxazole (Sul) in cell structure during electrochemical flow through reaction (EFTR) process was firstly reported. Meanwhile, EFTR treatment possessed excellent disinfection performance and consequently controlled the HGT risks. The intracellular Tet (iTet) was discharged through efflux pumps to increase the content of extracellular Tet (eTet) due to the resistance of donor E. coli DH5α under the selective pressure of Tet, declining the damage of donor and plasmid RP4. The HGT frequency was 8.18-fold increase compared with that by EFTR treatment alone. While the secretion of intracellular Sul (iSul) was inhibited by blocking the formation of efflux pumps to inactivate the donor under the Sul pressure, and the total content of iSul and adsorbed Sul (aSul) to be 1.36-fold higher than that of eSul. Therefore, the reactive oxygen species (ROS) generation and cell membrane permeability were improved to release ARGs, and •OH attacked plasmid RP4 in the EFTR process, inhibiting the HGT risks. This study advances the awareness of the interaction between distribution of different antibiotics in cell structure and the HGT risks in the EFTR process.

Augmented dissemination of antibiotic resistance elicited by non-antibiotic factors

The emergence and rapid spread of antibiotic resistance seriously compromise the clinical efficacy of current antibiotic therapies, representing a serious public health threat worldwide. Generally, drug-susceptible bacteria can acquire antibiotic resistance through genetic mutation or gene transfer, among which horizontal gene transfer (HGT) plays a dominant role. It is widely acknowledged that the sub-inhibitory concentrations of antibiotics are the key drivers in promoting the transmission of antibiotic resistance. However, accumulating evidence in recent years has shown that in addition to antibiotics, non-antibiotics can also accelerate the horizontal transfer of antibiotic resistance genes (ARGs). Nevertheless, the roles and potential mechanisms of non-antibiotic factors in the transmission of ARGs remain largely underestimated. In this review, we depict the four pathways of HGT and their differences, including conjugation, transformation, transduction and vesiduction. We summarize non-antibiotic factors accounting for the enhanced horizontal transfer of ARGs and their underlying molecular mechanisms. Finally, we discuss the limitations and implications of current studies.

Deciphering the dynamics of metal and antibiotic resistome profiles under different metal(loid) contamination levels

Metal(loid) contaminations pose considerable threats to ecological security and public health, yet little is known about the dynamics of metal resistance genes (MRGs) and antibiotic resistance genes (ARGs) under different metal(loid) contamination levels. Here, we provided a systematic investigation of MRGs and ARGs in three zones (Zones I, II, and III) with different metal(loid) contamination levels across an abandoned sewage reservoir. More diverse MRGs and ARGs were detected from the high-contaminated Zone I and the moderate-contaminated Zone II, while the abundant MGEs (mobile genetic elements) potentially enhanced the horizontal gene transfer potential and the resistome diversity in Zone I. Particularly, resistome hosts represented by Thiobacillus, Ramlibacter, and Dyella were prevalent in Zone II, promoting the vertical gene transfer of MRGs and ARGs. The highest health risk of ARGs was predicted for Zone I (about 7.58% and 0.48% of ARGs classified into Rank I and Rank II, respectively), followed by Zone II (2.11% and 0%) and Zone III (0% and 0%). However, the ARGs co-occurring with MRGs might exhibit low proportions and low health risks (all were Rank IV) in the three zones. Overall, these findings uncovered the dynamic responses of resistomes and their hosts to different metal(loid) contamination levels, contributing to formulating accurate management and bioremediation countermeasures for various metal(loid) contaminated environments.

Hormetic Effect of Pyroligneous Acids on Conjugative Transfer of Plasmid-mediated Multi-antibiotic Resistance Genes within Bacterial Genus

Spread of antibiotic resistance genes (ARGs) by conjugation poses great challenges to public health. Application of pyroligneous acids (PA) as soil amendments has been evidenced as a practical strategy to remediate pollution of ARGs in soils. However, little is known about PA effects on horizontal gene transfer (HGT) of ARGs by conjugation. This study investigated the effects of a woody waste-derived PA prepared at 450°C and its three distillation components (F1, F2, and F3) at different temperatures (98, 130, and 220°C) on conjugative transfer of plasmid RP4 within Escherichia coli. PA at relatively high amount (40-100 μL) in a 30-mL mating system inhibited conjugation by 74-85%, following an order of PA > F3 ≈ F2 ≈ F1, proving the hypothesis that PA amendments may mitigate soil ARG pollution by inhibiting HGT. The bacteriostasis caused by antibacterial components of PA, including acids, phenols, and alcohols, as well as its acidity (pH 2.81) contributed to the inhibited conjugation. However, a relatively low amount (10-20 μL) of PA in the same mating system enhanced ARG transfer by 26-47%, following an order of PA > F3 ≈ F2 > F1. The opposite effect at low amount is mainly attributed to the increased intracellular reactive oxygen species production, enhanced cell membrane permeability, increased extracellular polymeric substance contents, and reduced cell surface charge. Our findings highlight the hormesis (low-amount promotion and high-amount inhibition) of PA amendments on ARG conjugation and provide evidence for selecting an appropriate amount of PA amendment to control the dissemination of soil ARGs. Moreover, the promoted conjugation also triggers questions regarding the potential risks of soil amendments (e.g., PA) in the spread of ARGs via HGT.

Effects and mechanisms of plant growth regulators on horizontal transfer of antibiotic resistance genes through plasmid-mediated conjugation

A vast number of bacteria occur in both soil and plants, with some of them harboring antibiotic resistance genes (ARGs). When bacteria congregate on the interface of soil particles or on plant root surfaces, these ARGs can be transferred between bacteria via conjugation, leading to the formation of antibiotic-resistant pathogens that threaten human health. Plant growth regulators (PGRs) are widely used in agricultural production, promoting plant growth and increasing crop yields. However, until now, little information has been known about the effects of PGRs on the horizontal gene transfer (HGT) of ARGs. In this study, with Escherichia coli DH5α (carrying RP4 plasmid with Tet^R, Amp^R, Kan^R) as the donor and E. coli HB101 as the recipient, a series of diparental conjugation experiments were conducted to investigate the effects of indoleacetic acid (IAA), ethel (ETH) and gibberellin (GA₃) on HGT of ARGs via plasmid-mediated conjugation. Furthermore, the mechanisms involved were also clarified. The results showed that all three PGRs affected the ARG transfer frequency by inducing the intracellular reactive oxygen species (ROS) formation, changing the cell membrane permeability, and regulating the gene transcription of traA, traL, trfAp, trbBp, kilA, and korA in plasmid RP4. In detail, 50-100 mg⋅L^-1 IAA, 20-50 mg⋅L^-1 ETH and 1500-2500 mg⋅L^-1 GA₃ all significantly promoted the ARG conjugation. This study indicated that widespread use of PGRs in agricultural production could affect the HGT of ARGs via plasmid-mediated conjugation, and the application of reasonable concentrations of PGRs could reduce the ARG transmission in both soil environments and plants.

Protein fractionation and shotgun proteomics analysis of enriched bacterial cultures shed new light on the enzymatically catalyzed degradation of acesulfame

The removal of organic micropollutants in municipal wastewater treatment is an extensively studied field of research, but the underlying enzymatic processes have only been elucidated to a small extent so far. In order to shed more light on the enzymatic degradation of the artificial sweetener acesulfame (ACE) in this context, we enriched two bacterial taxa which were not yet described to be involved in the degradation of ACE, an unknown Chelatococcus species and Ensifer adhaerens, by incubating activated sludge in chemically defined media containing ACE as sole carbon source. Cell-free lysates were extracted, spiked with ACE and analyzed via target LC-MS/MS, demonstrating for the first time enzymatically catalyzed ACE degradation outside of living cells. Fractionation of the lysate via two-dimensional fast protein liquid chromatography (FPLC) succeeded in a partial separation of the enzymes catalyzing the initial transformation reaction of ACE from those catalyzing the further transformation pathway. Thereby, an accumulation of the intermediate transformation product acetoacetamide-n-sulfonic acid (ANSA) in the ACE-degrading fractions was achieved, providing first quantitative evidence that the cleavage of the sulfuric ester moiety of ACE is the initial transformation step. The metaproteome of the enrichments was analyzed in the FPLC fractions and in the unfractionated lysate, using shotgun proteomics via UHPLC-HRMS/MS and label-free quantification. The comparison of protein abundances in the FPLC fractions to the corresponding ACE degradation rates revealed a metallo-β-lactamase fold metallo-hydrolase as most probable candidate for the enzyme catalyzing the initial transformation from ACE to ANSA. This enzyme was by far the most abundant of all detected proteins and amounted to a relative protein abundance of 91% in the most active fraction after the second fractionation step. Moreover, the analysis of the unfractionated lysate resulted in a list of further proteins possibly involved in the transformation of ACE, most striking a highly abundant amidase likely catalyzing the further transformation of ANSA, and an ABC transporter substrate-binding protein that may be involved in the uptake of ACE into the cell.

Different acesulfame potassium fate and antibiotic resistance propagation pattern in nitrifying and denitrifying sludge systems

Acesulfame potassium (ACE-K) is a widely utilized sugar substitute with increasing demand, which is frequently detected in various environmental matrix due to recalcitrance. However, a general consensus on the contribution of nitrifying and denitrifying process to ACE-K removal is lacking. Therefore, ACE-K removal, its effects on antibiotic resistant genes (ARGs) propagation and microbial community in nitrifying sequencing batch reactor (N-SBR) and denitrifying sequencing batch reactor (D-SBR) inoculated with the identical activated sludge were investigated. In this study, ACE-K can be eliminated in N-SBR with satisfying removal efficiency (96.76 ± 8.33 %) after 13 d acclimation, while it remained persistent (average ACE-K removal efficiency of 2.24 ± 1.86 %) in D-SBR during 84 d exposure. Moreover, ACE-K hardly affected the performances of these two types of reactors and had little impact on nitrifying and denitrifying functional genes. However, initial contact with ACE-K would increase ARGs abundance, network analysis showed functional bacteria in each reactor were possible ARGs hosts. Potential ACE-K degrading genera Chelatococcus, Bosea and Aquamicrobium were found in both reactors. LefSe analysis showed that Phyllobacteriaceae containing Aquamicrobium genus was a differentially enriched family in N-SBR. This research might provide a perspective for better understanding factor affecting ACE-K fate in wastewater treatment process and its ecological risks.

Unraveling the impact and mechanism of antipyretic paracetamol on intergenera conjugative plasmid transfer

Antimicrobial resistance has been considered as a great threat to biosecurity and human health. And the transmission of antibiotic resistance genes (ARGs) by conjugated plasmid is a key factor in the prevalence of antimicrobial resistance. Paracetamol (PRC), one of nonopioid analgesics, is an extensively used antipyretic and mild analgesic worldwide available for numerous prescriptions. It was unclear whether PRC could promote the spread of ARGs. Here, it was demonstrated that PRC promoted intergenera conjugative plasmid transfer in an established conjugation model. Both donor and recipient strains treated by PRC emerged the variations of reactive oxygen species (ROS), SOS response and cell membrane permeability. Correspondingly, transcriptome analysis revealed that the gene expression involved in cell membrane permeability and SOS response was up-regulated significantly after PRC exposure. More directly, PRC also increased the expressions of conjugation related genes of trbG and trbP in donor. This study proved for the first time that PRC could enhance the intergenera conjugative plasmid transfer. Collectively, these findings manifested the potential threat associated with the existence of non-antibiotic substance PRC, which could provide an important insight into antimicrobial resistance spread.

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.

Effects of trace PFOA on microbial community and metabolisms: Microbial selectivity, regulations and risks

Perfluorooctanoic acid (PFOA), a "forever chemical", is continuously discharged and mitigated in the environment despite its production and use being severely restricted globally. Due to the transformation, attachment, and adsorption of PFOA in aquatic environments, PFOA accumulates in the porous media of sediments, soils, and vadose regions. However, the impact of trace PFOA in the porous media on interstitial water and water safety is not clear. In this work, we simulated a porous media layer using a sand column and explored the effects of µg-level PFOA migration on microbial community alternation, microbial function regulation, and the generation and spread of microbial risks. After 60 days of PFOA stimulation, Proteobacteria became the dominant phylum with an abundance of 91.8%, since it carried 71% of the antibiotic resistance genes (ARGs). Meanwhile, the halogen-related Dechloromonas abundance increased from 0.4% to 10.6%. In addition, PFOA significantly stimulated protein (more than 1288%) and polysaccharides (more than 4417%) production by up-regulating amino acid metabolism (p< 0.001) and membrane transport (p < 0.001) to accelerate the microbial aggregation. More importantly, the rapidly forming biofilm immobilized and blocked PFOA. The more active antioxidant system repaired the damaged cell membrane by significantly up-regulating glycerophospholipid metabolism and peptidoglycan biosynthesis. It is worth noting that PFOA increased the abundance of antibiotic resistance genes (ARGs) and human bacterial pathogens (HBPs) in porous media by 30% and 106%. PFOA increased the proportion of vertical transmission ARGs (vARGs), and co-occurrence network analysis (r ≥ 0.8, p ≤ 0.01) verified that vARGs were mainly mediated by HBPs. A comprehensive understanding of PFOA interactions with its microecological environment is provided.

Accelerated spread of antibiotic resistance genes (ARGs) induced by non-antibiotic conditions: Roles and mechanisms

The global spread of antibiotic resistance genes (ARGs) has wreaked havoc with the treatment efficiency of antibiotics and, ultimately, anti-microbial chemotherapy, and has been conventionally attributed to the abuse and misuse of antibiotics. However, the ancient ARGs have alterative functions in bacterial physiology and thus they could be co-regulated by non-antibiotic conditions. Recent research has demonstrated that many non-antibiotic chemicals such as microplastics, metallic nanoparticles and non-antibiotic drugs, as well as some non-antibiotic conditions, can accelerate the dissemination of ARGs. These results suggested that the role of antibiotics might have been previously overestimated whereas the effects of non-antibiotic conditions were possibly ignored. Thus, in an attempt to fully understand the fate and behavior of ARGs in the eco-system, it is urgent to critically highlight the role and mechanisms of non-antibiotic chemicals and related environmental factors in the spread of ARGs. To this end, this timely review assessed the evolution of ARGs, especially its function alteration, summarized the non-antibiotic chemicals promoting the spread of ARGs, evaluated the non-antibiotic conditions related to ARG dissemination and analyzed the molecular mechanisms related to spread of ARGs induced by the non-antibiotic factors. Finally, this review then provided several critical perspectives for future research.

Preharvest Environmental and Management Drivers of Multidrug Resistance in Major Bacterial Zoonotic Pathogens in Pastured Poultry Flocks

Due to nutritional benefits and perceived humane ways of treating the animals, the demand for antibiotic-free pastured poultry chicken has continued to be steadily rise. Despite the non-usage of antibiotics in pastured poultry broiler production, antibiotic resistance (AR) is reported in zoonotic poultry pathogens. However, factors that drive multidrug resistance (MDR) in pastured poultry are not well understood. In this study, we used machine learning and deep learning approaches to predict farm management practices and physicochemical properties of feces and soil that drive MDR in zoonotic poultry pathogens. Antibiotic use in agroecosystems is known to contribute to resistance. Evaluation of the development of resistance in environments that are free of antibiotics such as the all-natural, antibiotic-free, pastured poultry production systems described here is critical to understand the background AR in the absence of any selection pressure, i.e., basal levels of resistance. We analyzed 1635 preharvest (feces and soil) samples collected from forty-two pastured poultry flocks and eleven farms in the Southeastern United States. CDC National Antimicrobial Resistance Monitoring System guidelines were used to determine antimicrobial/multidrug resistance profiles of Salmonella, Listeria, and Campylobacter. A combination of two traditional machine learning (RandomForest and XGBoost) and three deep learning (Multi-layer Perceptron, Generative Adversarial Network, and Auto-Encoder) approaches identified critical farm management practices and environmental variables that drive multidrug resistance in poultry pathogens in broiler production systems that represents background resistance. This study enumerates management practices that contribute to AR and makes recommendations to potentially mitigate multidrug resistance and the prevalence of Salmonella and Listeria in pastured poultry.

Food Additives Associated with Gut Microbiota Alterations in Inflammatory Bowel Disease: Friends or Enemies?

During the 21st century, the incidence and prevalence of inflammatory bowel disease (IBD) is rising globally. Despite the pathogenesis of IBD remaining largely unclear, the interactions between environmental exposure, host genetics and immune response contribute to the occurrence and development of this disease. Growing evidence implicates that food additives might be closely related to IBD, but the involved molecular mechanisms are still poorly understood. Food additives may be categorized as distinct types in accordance with their function and property, including artificial sweeteners, preservatives, food colorant, emulsifiers, stabilizers, thickeners and so on. Various kinds of food additives play a role in modifying the interaction between gut microbiota and intestinal inflammation. Therefore, this review comprehensively synthesizes the current evidence on the interplay between different food additives and gut microbiome alterations, and further elucidates the potential mechanisms of food additives–associated microbiota changes involved in IBD.

Alteration in microbial community and antibiotic resistance genes mediated by microplastics during wastewater ultraviolet disinfection

Microplastics (MPs) could be as a vector to colonize microorganisms and antibiotic resistance gene (ARGs) in surface water. However, little information is known regarding their changes by the presence of MPs in wastewater treatment. Here, the effects of different concentrations and sizes of polystyrene microplastics (PSMPs) on the distribution and removal of microbial communities and ARGs under ultraviolet disinfection of urban sewage have been systematically studied. Results showed that the presence of MPs altered abundance and functions of microorganisms in wastewater, despite different effects on different types of microorganisms. The most abundant ARGs in original disinfection tank sewage was rpoB2 (6.34%). A certain concentration range of MPs can improve the ability of specific types of ARGs in the UV disinfection process. Compared to the system without PSMPs, the content of Deinococcus-Thermus and Bacteroidetes phylum increased, while Actinobacteria and Proteobacteria phylum decreased in the presence of MPs. The microbial functions, especially the genetic information processing and metabolism were altered by the presence of PSMPs. In addition, PSMPs altered the content of ARGs, where the contents of OXA-182 and ErmH were increased, while adeF and ANT3-Iic were decreased. PSMPs also decreased the free ARB content in wastewater by providing colonization sites. The UV disinfection efficiency of microorganisms and ARGs was also intervened by PSMPs since they provided colonization sites and increased the water turbidity. The findings indicated that PSMPs altered the distribution and removal of microbial community and ARGs in ultraviolet disinfection of wastewater, highlighting the combined risks.

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

The harmful effects of antibiotics on biological denitrification have attracted widespread attention due to their excessive usage. Polymyxin B (PMB) as the typical antimicrobial peptides having been regarded as the "last hope" for treatment of multidrug-resistance bacteria, has also been detected in wastewater. However, little is known about the influence of PMB on aerobic denitrification. In this study, the impact of PMB on aerobic denitrification performance was investigated. Results showed 0.50 mg/L PMB decreased nitrate removal efficiency from 97.4% to 85.3%, and drove denitrifiers to transform more nitrate to biomass instead of producing gas-N. The live/dead staining method showed PMB damaged bacterial membrane. Transcriptome analysis further indicated the key enzymes participating in denitrification and aerobic respiratory chains were suppressed by PMB. To resist the PMB stress, denitrifiers formed thicker biofilm to protect cells from PMB damaging and thus remodeling the central carbon metabolism. Further investigation revealed denitrifiers have different preference on various carbon sources when PMB is present. Subsequently, the underlying mechanism of the distinctive carbon sources preference was explored by the combination of transcriptome and metabolism analysis. Overall, our data suggested denitrifiers have distinctive carbon sources preference under PMB treatment conditions, reminding us that carbon source selection should be cautious in practical applications.

Chloroxylenol at environmental concentrations can promote conjugative transfer of antibiotic resistance genes by multiple mechanisms

The intergeneric conjugative transfer of antibiotic resistance genes (ARGs) is recognized as an important way to the dissemination of antibiotic resistance. However, it is unknown whether the extensive use of chloroxylenol (para-chloro-meta-xylenol, PCMX) in many pharmaceutical personal care products will lead to the spread of ARGs. In this study, the abilities and mechanisms of PCMX to accelerate the intergeneric conjugative transfer were investigated. Results showed that exposure of bacteria to environmental concentrations of PCMX (0.20-1.00 mg/L) can significantly stimulate the increase of conjugative transfer by 8.45-9.51 fold. The phenotypic experiments and genome-wide RNA sequencing revealed that 0.02-5.00 mg/L PCMX exposure could increase the content of alkaline phosphatase and malondialdehyde, which are characteristic products of cell wall and membrane damage. In addition, PCMX could lead to excessive production of reactive oxygen species (ROS) by 1.26-2.00 times, the superoxide dismutase and catalase produced by bacteria in response to oxidative stress were not enough to neutralize the damage of ROS, thus promoting the conjugative transfer. Gene Ontology enrichment analysis indicated that cell membrane permeability, pili, some chemical compounds transport and energy metabolism affected conjugative transfer. This study deepened the understanding of PCMX in promoting propagation of ARGs, and provided new perspectives for use and treatment of personal care products.