Transfer Frequency Research Articles

Damage-free Non-mechanical Transfer Strategy for Highly Transparent, Stretchable Embedded Metallic Micromesh Electrodes

Stretchable, flexible, transparent electrodes garner significant research interest as indispensable components of flexible optoelectronic devices. However, frequent mechanical transfers during processing pose a considerable challenge in preparing electrodes of scalable size with superior performance and intact structure. Herein, we present a stretchable embedded metallic micromesh (SEMM) electrode with high optoelectronic and robust mechanical properties. The SEMM electrode is fabricated via a damage-free non-mechanical transfer strategy with the assistance of a bifunctional metal transition layer that serves as both a seed layer during electrodeposition and a sacrificial layer during stripping of the electrode. Consequently, the SEMM electrode features a scalable size and an intact structure. By optimizing the electrodeposition parameters, the SEMM achieves high optical transmittance (∼83%) and low sheet resistance (0.22 Ω sq-1), with a figure of merit reaching 8600 – 53 times greater than that of commercial polyethylene terephthalate-indium tin oxide (PET-ITO). Furthermore, the SEMM exhibits excellent mechanical stability, enduring up to 60% of tensile strain and maintaining almost constant normalized resistance after 20,000 bending cycles. Based on the SEMM, a transparent film heater yields rapid response time, low operating voltage, and fast defogging capability. This non-mechanical transfer strategy offers a compelling approach for enhancing the structural integrity and scalability of stretchable embedded transparent electrodes.

Supercritical mechano-exfoliation process

The intricate balance among cost, output, and quality has substantially hindered the practical application of graphene within the downstream industry chain. Here we present a scalable and green supercritical CO2-assisted mechano-exfoliation (SCME) process that omits the use of organic solvents and oxidants throughout the production lifecycle, including exfoliation, separation, and purification. The SCME process achieves graphene powder space-time yields exceeding 40 kg/(m³·day) at laboratory (0.06–0.2 kg) and pilot scales ( > 4 kg), with resultant free-standing films showing conductivities up to 5.26 × 10⁵ S/m. Further kinetic investigations propose general guidelines for grinding-assisted exfoliation: (1) the macroscopic optimizing ability of mechanotechnics for mass transfer frequency and stress distribution and (2) the microscopic multiplication ability of exfoliation medium for shear-delamination. The comprehensive techno-economic analysis also underscores the economic viability of the SCME process for large-scale production.

Non-linear cascade control with gain-scheduling and startup control strategy study for thermionic space reactor TOPAZ-II

The TOPAZ-II thermionic space reactor system, which was designed by the Soviet Union, is characterized by its high degree of nonlinearity and positive temperature reactivity feedback. The thermionic space reactor exhibits characteristics of high inertia and significant delay in controlling its electrical power and outlet temperature. The simple PID controller is difficult to achieve good performance. To carry out controller design for thermionic space reactor, the simulation platform for thermionic space reactor is developed based on coupling between reactor system thermal-hydraulic code RESYS and control system simulator in this study. After that, based on the cascade control strategy and gain-scheduling, the reactor thermal controller, electric power controller, outlet temperature controller applicable for the full power range is designed with transfer function model and frequency domain analysis method. To validate the nonlinear electric power controller performance, the continuous minor step disturbances, major step disturbances, and ramp variation of electric power setpoint is simulated. The performance of outlet temperature controller is verified with the simulation result of step and ramp variation of outlet temperature setpoint. Thereafter, the start-up process of the thermionic space reactor TOPAZ-II is simulated and analyzed. The simulation result reveals that the controller designed in this paper can overcome the nonlinearity of the thermionic space reactor system and has good performance throughout the entire power range. Compared to traditional simple PID controller, the cascade controller has better performance and can achieve good control performance even in situations where simple PID controllers cannot function properly.

Evaluation of antibiotics resistance and transmission risk of Escherichia coli in rice-frog coculture system

In order to assess the antibiotic resistance of Escherichia coli and its transmission risk in a rice-frog coculture system in Zhejiang Province, this study collected E. coli from isolated soil, field water, and frog feces from the rice-frog coculture systems in four different areas of Zhejiang Province. The collected isolates were identified by 16S rRNA sequencing, while their antibiotic-resistant phenotypes were determined by Kirby-Bauer (K-B) method. PCR was used to identify the antibiotic-resistant genotypes and integrons, while conjugative transfer experiments were used to assess resistance transmission characteristics. The results showed a high prevalence of antibiotic resistance in the 82 strains of E. coli tested, primarily against tetracycline, sulfisoxazole, amoxicillin, and erythromycin. Most of these strains exhibited multidrug resistance, with the Fuyang area demonstrating the highest resistance rate compared to the other three areas. Further PCR analysis identified the sul1 gene as the most frequently detected resistance gene (63.41%), followed by blaTEM, tetA, and tetB. Among the 16 antibiotic resistance genes (ARGs) detected, the Fuyang isolates consistencly exhibited higher detection rate of 9 ARGs in comparison to the other regions. Additionally, the integrase gene intI1 displayed the highest detection rate, with 14 strains (34.15%) of integrase-positive bacteria carrying gene cassettes. Four different gene cassette compositions were observed, with dfrA1-aadA1 and dfrA17-aadA5 being the most common combinations. Conjugative transfer experiments demonstrated successful transfer of gene cassettes in 4 out of 14 donor bacteria, with conjugation transfer frequencies ranging from 4.32×10-5 to 7.13×10-4. These findings revealed the severity of resistance in the Fuyang area among the four regions. Integrons play a significant role in mediating the resistance to multiple antibiotics in E. coli, facilitating the potential spread of resistance gene cassettes between different bacteria. Overall, this study provides valuable insights into the resistance status and transmission characteristics of E. coli in the rice-frog coculture system in Zhejiang Province, providing a theoretical basis for ensuring the food safety of rice crops.

Investigation of Arc Stability in Wire Arc Additive Manufacturing of 2319 Aluminum Alloy

Wire Arc Additive Manufacturing (WAAM) technology, known for its low equipment and material costs, high material utilization, and high production efficiency, has found extensive applications in the fabrication of key components for the aerospace and aviation industries. The stability of the arc is crucial for the WAAM process as it directly affects the forming of the parts. In this study, the monitoring data of electrical signals and arc morphology during the WAAM process of 2319 aluminum alloy were investigated using a high-speed camera system and current/voltage acquisition system. By analyzing the current and voltage signals, as well as the arc imaging results, the influence of arc stability on the forming of the cladding layer was studied. The experimental results indicated that when both current and voltage exhibit regular periodic fluctuations, this manifests as a stable short-circuit droplet transition form, while sudden changes in these signals represent abnormal droplet transition forms. The adaptability of the process directly influenced the arc shape, thereby affecting the forming of the cladding layer. Under the process parameters of welding speed of 240 cm/min and wire feeding speed of 6.5 m/min, it was observed that the current signal exhibited a tight state and the variance of the arc width was minimized. This indicated that at a higher wire feeding speed, the droplet transfer frequency was increased. Under these process parameters, the arc output was more stable, resulting in a uniform metal coating.

Insights into kinetic and transfer mechanisms for alkaline decoupled water electrolysis based on distribution of relaxation times

Electrochemical water splitting is crucial for the decarbonization of industrial processes and the coupling of renewable energy sources. Evaluation of individual HER and OER contributions to the transfer process is essential for optimizing electrolysis system performance. This study uses nickel-cobalt layered double hydroxide (NiCo-LDH) as a solid-state redox mediator (SRM), achieving efficient H2 and O2 separation. This study provides an in-depth analysis of kinetic and ion/charge/mass transfer mechanisms linked to various characteristic impedances in alkaline decoupled water electrolysis (DWE) system by integrating Electrochemical Impedance Spectroscopy (EIS) and Distribution of Relaxation Times (DRT) methods. The characteristic frequency evolution is consistent with the charge-discharge state of SRM and mass transfer frequency is related to the bubble size and gas diffusion rate of electrocatalysts at different current densities. The charge transfer Rct dominates the total polarization impedance in decoupled HER, and mass transfer Rm decreases remarkably in decoupled OER. OER shows lower Rct with Fe species existence and lower total polarization impedance than HER. Rm in decoupled HER increases by 38.24% and OER by 29.82% during prolonged decoupled test. This study provides valuable insights into the impedance contributions and kinetic mechanisms through novel electrolysis approaches, guiding further optimization of decoupled electrolyzer and electrode.

Improving microstructure and mechanical properties of WAAMed Al with UV introduced via a torch clamp

Abstract Ultrasonic assisting is considered to be a promising technology for industrial applications due to its ability to improve the quality of the WAAMed component. A specially designed ultrasonically vibrating torch clamp (UV torch clamp) was used to introduce the UV in the WAAM process of Al alloy for the first time. UV effect on the forming accuracy, microstructure and mechanical properties of WAAMed Al thin-walled component were investigated. The results show that the UV applied via the UV torch clamp changed the metal transfer mode, and increased the transfer frequency by at least 7.42% compared with that without UV at various Wire Feed Speed (WFSs). The applied UV caused slight increases in the surface roughness of the deposited thin-wall components at low WFSs and obvious decreases at high WFSs, the most significant reduction occurred with WFS = 8 m min−1, the surface roughness decreased from 1.04 to 0.44. The grain size and the pore size and density in the deposit were significantly reduced by the UV, and the higher the WFS, the greater the grain refinement effectiveness and the pore suppression effectiveness. The UTS and fracture elongation of the specimen with UV application increased by at least 4.6% (from 277 Mpa to 290 Mpa for longitudinal specimen with WFS = 5 m min−1, ) and 3.3% (from 21.42% to 22.12% for vertical specimen with WFS = 8 m min−1) respectively at various WFSs compared to the specimen without UV application.

Genomic epidemiology of carbapenem-resistant Enterobacterales at a New York City hospital over a 10-year period reveals complex plasmid-clone dynamics and evidence for frequent horizontal transfer of bla KPC.

Transmission of carbapenem-resistant Enterobacterales (CRE) in hospitals has been shown to occur through complex, multifarious networks driven by both clonal spread and horizontal transfer mediated by plasmids and other mobile genetic elements. We performed nanopore long-read sequencing on CRE isolates from a large urban hospital system to determine the overall contribution of plasmids to CRE transmission and identify specific plasmids implicated in the spread of bla KPC (the Klebsiella pneumoniae carbapenemase [KPC] gene). Six hundred and five CRE isolates collected between 2009 and 2018 first underwent Illumina sequencing for genome-wide genotyping; 435 bla KPC-positive isolates were then successfully nanopore sequenced to generate hybrid assemblies including circularized bla KPC-harboring plasmids. Phylogenetic analysis and Mash clustering were used to define putative clonal and plasmid transmission clusters, respectively. Overall, CRE isolates belonged to 96 multilocus sequence types (STs) encoding bla KPC on 447 plasmids which formed 54 plasmid clusters. We found evidence for clonal transmission in 66% of CRE isolates, over half of which belonged to four clades comprising K. pneumoniae ST258. Plasmid-mediated acquisition of bla KPC occurred in 23%-27% of isolates. While most plasmid clusters were small, several plasmids were identified in multiple different species and STs, including a highly promiscuous IncN plasmid and an IncF plasmid putatively spreading bla KPC from ST258 to other clones. Overall, this points to both the continued dominance of K. pneumoniae ST258 and the dissemination of bla KPC across clones and species by diverse plasmid backbones. These findings support integrating long-read sequencing into genomic surveillance approaches to detect the hitherto silent spread of carbapenem resistance driven by mobile plasmids.

Microplastic biofilms promote the horizontal transfer of antibiotic resistance genes in estuarine environments

As emerging pollutants, microplastics can aggregate microorganisms on their surfaces and form biofilms, enriching antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs). Consequently, microplastic biofilms have become a focal point of research. Horizontal gene transfer is one of the primary mechanisms by which bacteria acquire antibiotic resistance, with much of the research focusing on suspended bacteria. However, microplastic biofilms, as hotspots for horizontal gene transfer, also merit significant investigation. This study primarily explored and compared the frequency of ARG conjugative transfer between suspended bacteria and microplastic biofilms. The results demonstrated that, compared to suspended bacteria, microplastic biofilms enhanced the frequency of ARG conjugative transfer by 7.2–19.6 times. Among them, biofilms on polyethylene microplastics showed the strongest promotion of conjugation. After the formation of microplastic biofilms, there was a significant increase in bacterial density within the biofilms, which raised the collision frequency of donor and recipient bacteria. Then microplastic biofilms facilitated the gene expression levels of outer membrane proteins, enhanced bacterial gene transfer capabilities, promoted the synthesis of conjugative pili, accelerated the formation of conjugative pairing systems, and elevated the expression levels of genes related to DNA replication and transfer systems, thereby enhancing the conjugative transfer of ARGs within microplastic biofilms. Among different types of microplastic biofilms, polyethylene biofilms exhibited the highest bacterial density, thus showing the highest frequency of ARG conjugation. This study highlights the risks associated with ARG conjugative transfer following the formation of microplastic biofilms and provides insights into the risks of microplastic and antibiotic resistance propagation in estuarine environments.

Evolution of the Tn4371 ICE family: traR-mediated coordination of cargo gene upregulation and horizontal transfer.

ICEKKS102Tn4677 carries a bph operon for the mineralization of polychlorinated biphenyls (PCBs)/biphenyl and belongs to the Tn4371 ICE (integrative and conjugative element) family. In this study, we investigated the role of the traR gene in ICE transfer. The traR gene encodes a LysR-type transcriptional regulator, which is conserved in sequence, positioning, and directional orientation among Tn4371 family ICEs. The traR belongs to the bph operon, and its overexpression on solid medium resulted in modest upregulation of traG (threefold), marked upregulation of xis (80-fold), enhanced ICE excision and, most notably, ICE transfer frequency. We propose the evolutional roles of traR, which upon insertion to its current position, might have connected the cargo gene activation and ICE transfer. This property of ICE, i.e., undergoing transfer under environmental conditions that lead to cargo gene activation, would instantly confer fitness advantages to bacteria newly acquiring this ICE, thereby resulting in efficient dissemination of the Tn4371 family ICEs.IMPORTANCEOnly ICEKKS102Tn4677 is proven to transfer among the widely disseminating Tn4371 family integrative and conjugative elements (ICEs) from β and γ-proteobacteria. We showed that the traR gene in ICEKKS102Tn4677, which is conserved in the ICE family with fixed location and direction, is co-transcribed with the cargo gene and activates ICE transfer. We propose that capturing of traR by an ancestral ICE to the current position established the Tn4371 family of ICEs. Our findings provide insights into the evolutionary processes that led to the widespread distribution of the Tn4371 family of ICEs across bacterial species.

The Angiopoietin-Tie-2 Axis in Children and Young Adults with Dengue Virus Infection in the Philippines.

Dengue virus (DENV) infection is associated with plasma leakage, which may progress to shock. The angiopoietin (Ang)-tyrosine kinase with immunoglobulin and epidermal growth factor homology domain 2 (Tie-2) axis regulates endothelial permeability. We examined the clinical utility of Ang-1, Ang-2, and the Ang-2-to-Ang-1 ratio for prediction of progression to severe DENV in a prospective cohort study of children and young adults (age 1 to <26 years) with DENV infection. Ang-1, Ang-2, Tie-2 were measured at presentation to an outpatient clinic in the Philippines from stored plasma by multiplex Luminex® assay. Patients were followed prospectively to document the clinical course (hospitalization, length of stay, intravenous fluid resuscitation, and transfer to a higher level facility). We included 244 patients (median age 9 years, 40% female). At presentation, 63 patients (26%) had uncomplicated dengue, 179 (73%) had dengue with warning signs, and 2 (0.82%) had severe dengue. One hundred eighty-one patients (74%) were hospitalized. Ang-1 levels were lower and Ang-2 higher in patients who required hospitalization. Ang-2-to-Ang-1 ratio >1 was associated with a relative risk of hospitalization of 1.20 (95% CI: 1.03-1.36, P = 0.016). A higher Ang-2-to-Ang-1 ratio was associated with longer length of hospital stay, higher frequency of transfer to a higher level facility, larger intravenous fluid requirement, hemoconcentration, and thrombocytopenia. Angiopoietin-2 was correlated with procalcitonin (Kendall's τ = 0.17, P = 0.00012), a marker of systemic inflammation, as well as soluble vascular cell adhesion molecule-1 (τ = 0.22, P <0.0001) and Endoglin (τ = 0.14, P = 0.0017), markers of endothelial activation. In conclusion, altered Ang-2-to-Ang-1 ratio can be detected early in the course of DENV infection and predicts clinically meaningful events (hospitalization, length of stay, and fluid resuscitation).

The effects of small plastic particles on antibiotic resistance gene transfer revealed by single cell and community level analysis

Small plastic particles with sizes comparable to bacterial cells, widely exist in environment. However, their effects on antibiotic resistance gene (ARG) dissemination remain unclear. Using polystyrene (PS) particles (0.2µm, 2µm, 5µm, 10µm, 15µm, 20µm) as models, conjugative transfer of ARGs between the donor E. coli and different recipients (E. coli or sludge bacterial community) was investigated. Compared to the pure strain, the sludge bacterial community exposed to PS particles showed higher transfer frequencies (1.67 to 14.31 times the blank control). The transfer frequencies first decreased and then increased with particle size, and plastics similar in size to bacteria (e.g., 2µm) appear to be a transitional zone with minimal impact on ARG transmission. Furthermore, using microfluidics, in-situ observation at single cell level found that 2µm plastics can act as barriers between donor and recipient bacteria inhibiting growth, but conjugation events mostly occurred around them. Conversely, nanoplastics (e.g., 0.2µm) and larger microplastics (e.g., 20µm) significantly promote conjugation, mainly due to increased reactive oxygen species production and cell membrane permeability, or facilitating bacterial adhesion and biofilm formation, respectively. This study aids in assessing environmental risks of small plastic particles on ARG dissemination.

Acetylshikonin reduces the spread of antibiotic resistance via plasmid conjugation

The plasmid-mediated conjugative transfer of antibiotic resistance genes (ARGs) stands out as the primary driver behind the dissemination of antimicrobial resistance (AMR). Developing effective inhibitors that target conjugative transfer represents an efficient strategy for addressing the issue of AMR. Here, we studied the effect of acetylshikonin (ASK), a botanical derivative, on plasmid conjugation. The conjugative transfer of RP4-7 plasmid inter and intra species was notably reduced by ASK. The conjugation process of IncI2 and IncX4 plasmids harboring the mobile colistin resistance gene (mcr-1), IncX4 and IncX3 plasmids containing the carbapenem resistance gene (blaNDM-5), and IncFI and IncFII plasmids possessing the tetracycline resistance gene [tet(X4)] were also reduced by ASK. Importantly, the conjugative transfer frequency of mcr-1 positive IncI2 plasmid in mouse peritoneal conjugation model and gut conjugation model was reduced by ASK. The mechanism investigation showed that ASK disrupt the functionality of the bacterial cell membrane. Furthermore, the proton motive force (PMF) was dissipated. In addition, ASK blocked the electron transmission in bacteria's electron transport chain (ETC) through disturbing the quinone interaction, resulting in an insufficient energy supply for conjugation. Collectively, ASK is a potential conjugative transfer inhibitor, providing novel strategies to prevent the spread of AMR.

Evolution of plant metabolism: the state-of-the-art.

Immense chemical diversity is one of the hallmark features of plants. This chemo-diversity is mainly underpinned by a highly complex and biodiverse biochemical machinery. Plant metabolic enzymes originated and were inherited from their eukaryotic and prokaryotic ancestors and further diversified by the unprecedentedly high rates of gene duplication and functionalization experienced in land plants. Unlike prokaryotic microbes, which display frequent horizontal gene transfer events and multiple inputs of energy and organic carbon, land plants predominantly rely on organic carbon generated from CO2 and have experienced relatively few gene transfers during their recent evolutionary history. As such, plant metabolic networks have evolved in a stepwise manner using existing networks as a starting point and under various evolutionary constraints. That said, until recently, the evolution of only a handful of metabolic traits had been extensively investigated and as such, the evolution of metabolism has received a fraction of the attention of, the evolution of development, for example. Advances in metabolomics and next-generation sequencing have, however, recently led to a deeper understanding of how a wide range of plant primary and specialized (secondary) metabolic pathways have evolved both as a consequence of natural selection and of domestication and crop improvement processes. This article is part of the theme issue 'The evolution of plant metabolism'.

Efficient control of antibiotic resistance in wastewater by UV/peracetic acid treatment: Unveiling distinct mechanisms behind the elimination of various contaminants

The abuse of antibiotics has led to an increase in contamination by antibiotics, antibiotic-resistant bacteria (ARB), and antibiotic resistance genes (ARGs) in the environment, especially in wastewater treatment plants, which are the main treatment sites for antibiotic contaminants. In this study, we demonstrated that the combined ultraviolet (UV)/peracetic acid (PAA) process effectively removes coexisting antibiotics, ARB, and ARGs simultaneously by removing 96 % of ampicillin (AMP, with an initial concentration of 10 μM) in 8 min and completely inactivating super-resistant Escherichia coli (E. coli) NDM-1 (i.e., achieving 7.44-log reduction) in just 3 min (PBS, pH=7.0). These bacteria did not proliferate during the 86-h bacterial regrowth test. The analysis of radical quenching and electron paramagnetic resonance revealed that reactive species, such as hydroxyl radicals (·OH) and carbon-centered organic radicals (R-C·), played dominant roles in AMP removal, whereas UV irradiation was crucial for ARB inactivation. Furthermore, the ARGs fragments were efficiently damaged, as demonstrated by gel electrophoresis analysis, leaving few intact sequences. This strategy effectively reduced the horizontal transfer frequency of ARGs. Subsequent evaluations of the stability and efficiency of UV/PAA for pollutant removal in real wastewater further affirmed the broad applicability of the UV/PAA process. This study revealed that UV/PAA system has the potential to alleviate the burden of antibiotic resistance and contribute to a better comprehension and application for novel technology to control antibiotic resistance spread.

High-throughput single-cell sequencing of activated sludge microbiome

Wastewater treatment plants (WWTPs) represent one of biotechnology's largest and most critical applications, playing a pivotal role in environmental protection and public health. In WWTPs, activated sludge (AS) plays a major role in removing contaminants and pathogens from wastewater. While metagenomics has advanced our understanding of microbial communities, it still faces challenges in revealing the genomic heterogeneity of cells, uncovering the microbial dark matter, and establishing precise links between genetic elements and their host cells as a bulk method. These issues could be largely resolved by single-cell sequencing, which can offer unprecedented resolution to show the unique genetic information. Here we show the high-throughput single-cell sequencing to the AS microbiome. The single-amplified genomes (SAGs) of 15,110 individual cells were clustered into 2,454 SAG bins. We find that 27.5% of the genomes in the AS microbial community represent potential novel species, highlighting the presence of microbial dark matter. Furthermore, we identified 1,137 antibiotic resistance genes (ARGs), 10,450 plasmid fragments, and 1,343 phage contigs, with shared plasmid and phage groups broadly distributed among hosts, indicating a high frequency of horizontal gene transfer (HGT) within the AS microbiome. Complementary analysis using 1,529 metagenome-assembled genomes from the AS samples allowed for the taxonomic classification of 98 SAG bins, which were previously unclassified. Our study establishes the feasibility of single-cell sequencing in characterizing the AS microbiome, providing novel insights into its ecological dynamics, and deepening our understanding of HGT processes, particularly those involving ARGs. Additionally, this valuable tool could monitor the distribution, spread, and pathogenic hosts of ARGs both within AS environments and between AS and other environments, which will ultimately contribute to developing a health risk evaluation system for diverse environments within a One Health framework.

Water temperature disturbance alters the conjugate transfer of antibiotic resistance genes via affecting ROS content and intercellular aggregation

Spread of antibiotic resistance genes (ARGs) in aquatic ecosystems poses a significant global challenge to public health. The potential effects of water temperature perturbation induced by specific water environment changes on ARGs transmission are still unclear. The conjugate transfer of plasmid-mediated ARGs under water temperature perturbation was investigated in this study. The conjugate transfer frequency (CTF) was only 7.16 × 10−7 at a constant water temperature of 5 °C, and it reached 2.18 × 10−5 at 30 °C. Interestingly, compared to the constant 5 °C, the water temperature perturbations (cooling and warming models between 5–30 °C) significantly promoted the CTF. Intracellular reactive oxygen species was a dominant factor, which not only directly affected the CTF of ARGs, but also functioned indirectly via influencing the cell membrane permeability and cell adhesion. Compared to the constant 5 °C, water temperature perturbations significantly elevated the gene expression associated with intercellular contact, cell membrane permeability, oxidative stress responses, and energy driven force for CTF. Furthermore, based on the mathematical model predictions, the stabilization times of acquiring plasmid maintenance were shortened to 184 h and 190 h under cooling and warming model, respectively, thus the water temperature perturbations promoted the ARGs transmission in natural conditions compared with the constant low temperature conditions.

Dynamic behavior regulation of droplet transfer based on arc-bubble control by ultrasound-induced during underwater wet welding

In comparison to welding in air, the periodic formation of unstable arc bubbles is a significant factor contributing to the unstable mass transfer process during underwater wet welding (UWW). Up to now, there is no ideal method to control droplet transfer and improve arc stability. In this study, the ultrasound-induced method (UIM) was used to regulate the droplet transition behavior and improve the process stability. The behavior features and key mechanisms of arc-bubble and droplet transfer induced by ultrasound were revealed with the employment of highspeed camera and X-ray observation, respectively. The incident angle of ultrasound was taken as a variable to reveal its effects and mechanism of action on the behaviors of arc bubble and droplet transfer, weld formation quality, microstructure, and property of weld joint. The results show that ultrasound-induced a new rising mode of arc bubble, which can significantly reduce the repulsive resistance that come from the bubble rising on the droplet transfer process. Compared with underwater wet welding without ultrasound, the average diameter of molten droplets reduces from 3.2 mm to 1.7 mm, and the droplet transfer frequency increases from 7.8 Hz to 13 Hz as the incident angle of ultrasound increases to 60°. In addition, the weld seam without obvious defects could be produced by UWW with UIM, of which the Variation coefficient of weld reinforcement is reduced from 21.3 to 11.6 and 17.4 at an ultrasonic incident angle of 30° and 45°. With increasing of ultrasound incident angle, it showed that the microhardness of the weld joint has a slight increase. In the heat-affected zone, the microhardness for the joint increased from 290 HV to 320 HV while the incident angle increased to 60°. This research shows that an appropriate incident angle of ultrasound can obtain good-quality joints which has a stable metal transfer process in underwater wet welding.

Mating Assay: Plating Below a Cell Density Threshold is Required for Unbiased Estimation of Plasmid Conjugation Frequency of RP4 Transfer Between E. coli Strains

Mating assays are common laboratory experiments for measuring the conjugation frequency, i.e. efficiency at which a plasmid transfers from a population of donor cells to a population of recipient cells. Selective plating remains a widely used quantification method to enumerate transconjugants at the end of such assays. However, conjugation frequencies may be inaccurately estimated because plasmid transfer can occur on transconjugant-selective plates rather than only during the intended mating duration. We investigated the influence of cell density on this phenomenon. We conducted mating experiments with IncPα plasmid RP4 harbored in Escherichia coli at a fixed cell density and mating conditions, inoculated a serial dilution of the mating mixture on transconjugant-selective plates or in transconjugant-selective broth, and compared the results to a model of cell-to-cell distance distribution. Our findings suggest that irrespective of the mating mode (liquid vs solid), the enumeration of transconjugants becomes significantly biased if the plated cell density exceeds 28 Colony Forming Unit (CFU)/mm2 (or 1.68•105 CFU/standard 9 cm Petri dish). This threshold is determined with a 95% confidence interval of ± 4 CFU/mm2 (± 2.46•104 CFU/standard 9 cm Petri dish). Liquid mating assays were more sensitive to this bias because the conjugation frequency of RP4 is several orders of magnitude lower in suspension compared to surface mating. Therefore, if selective plating is used, we recommend to plate at this density threshold and that negative controls are performed where donors and recipients are briefly mixed before plating at the same dilutions as for the actual mating assay. As an alternative, a liquid enumeration method can be utilized to increase the signal-to-noise ratio and allow for more accurate enumeration of transconjugants.

Enhanced removal of antibiotic-resistant bacteria and resistance genes by three-dimensional electrochemical process using MgFe2O4-loaded biochar as both particle electrode and catalyst for peroxymonosulfate activation

In this study, MgFe2O4-loaded biochar (MFBC) was used as a three-dimensional particle electrode to active peroxymonosulfate (EC/MFBC/PMS) for the removal of antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs). The results demonstrated that, under the conditions of 1.0 mM PMS concentration, 0.4 g/L material dosage, 5 V voltage intensity, and MFBC preparation temperature of 600 °C, the EC/MFBC600/PMS system achieved complete inactivation of E. coli DH5α within 5 min and the intracellular sul1 was reduced by 81.5 % after 30 min of the treatment. Compared to EC and PMS alone treatments, the conjugation transfer frequency of sul1 rapidly declined by 92.9 % within 2 min. The cell membrane, proteins, lipids, as well as intracellular and extracellular ARGs in E. coli DH5α were severely damaged by free radicals in solution and intracellular reactive oxygen species (ROS). Furthermore, up-regulation was observed in genes associated with oxidative stress, SOS response and cell membrane permeability in E. coli DH5α, however, no significant changes were observed in functional genes related to gene conjugation and transfer mechanisms. This study would contribute to the underlying of PMS activation by three-dimensional particle electrode, and provide novel insights into the mechanism of ARB inactivation and ARGs degradation under PMS advanced oxidation treatment.