Bacterial Accumulation Research Articles

Inhibitory Effects of Dabigatran on Airway Inflammation Induced by Lipopolysaccharide in Mice

Asthma and chronic obstructive pulmonary disease (COPD) are characterised by chronic inflammation in the lung that is associated with airway obstruction. Inhaled therapy with a combination of corticosteroid and a long-acting β2-agonist is an effective anti-inflammatory medicine for asthma, but in patients with severe asthma and COPD fails to completely control these symptoms with current therapies. The inflammatory process in these diseases, which involves activation of the coagulation and fibrinolytic system in the lung, offers the opportunity for alternative anti-inflammatory therapies. In this study, we investigated the effects of anti-coagulants on lipopolysaccharide (LPS)-induced airway inflammation in mice. A/J mice were exposed to LPS, a bacterial endotoxin, intranasally and accumulation of inflammatory cells, TNF-α, C-X-C motif chemokine (CXCL) 1, and osteopontin in bronchoalveolar lavage fluid (BALF) was monitored by flow cytometry and an enzyme-linked immunosorbent assay. LPS exposure induced airway neutrophilia and accumulation of TNF-α, CXCL1, and osteopontin in BALF. This LPS-induced airway inflammation was not relieved using a corticosteroid, fluticasone propionate (FP), or a direct inhibitor of Factor Xa, rivaroxaban. In contrast, a direct thrombin inhibitor, dabigatran, inhibited LPS-induced airway neutrophilia and decreased inflammatory cytokine production in a dose dependent manner. Furthermore, combination of dabigatran and FP elicited stronger inhibition of LPS-induced airway inflammation. Therefore, these results suggest that dabigatran could be an effective new therapy for severe respiratory diseases.

Mucosal CD8 T Cell Responses Are Shaped by Batf3-DC After Foodborne Listeria monocytogenes Infection

While immune responses have been rigorously examined after intravenous Listeria monocytogenes (Lm) infection, less is understood about its dissemination from the intestines or the induction of adaptive immunity after more physiologic models of foodborne infection. Consequently, this study focused on early events in the intestinal mucosa and draining mesenteric lymph nodes (MLN) using foodborne infection of mice with Lm modified to invade murine intestinal epithelium (InlAM Lm). InlAM Lm trafficked intracellularly from the intestines to the MLN and were associated with Batf3-independent dendritic cells (DC) in the lymphatics. Consistent with this, InlAM Lm initially disseminated from the gut to the MLN normally in Batf3–/– mice. Activated migratory DC accumulated in the MLN by 3 days post-infection and surrounded foci of InlAM Lm. At this time Batf3–/– mice displayed reduced InlAM Lm burdens, implicating cDC1 in maximal bacterial accumulation in the MLN. Batf3–/– mice also exhibited profound defects in the induction and gut-homing of InlAM Lm-specific effector CD8 T cells. Restoration of pathogen burden did not rescue antigen-specific CD8 T cell responses in Batf3–/– mice, indicating a critical role for Batf3 in generating anti-InlAM Lm immunity following foodborne infection. Collectively, these data suggest that DC play diverse, dynamic roles in the early events following foodborne InlAM Lm infection and in driving the establishment of intestinal Lm-specific effector T cells.

A sol–gel based silver nanoparticle/polytetrafluorethylene (AgNP/PTFE) coating with enhanced antibacterial and anti-corrosive properties

In this research, a silver nanoparticle/polytetrafluorethylene (AgNP/PTFE) coating for metallic implants was fabricated using a facile layer-by-layer coating method. PTFE nanoparticles were immobilized in a sol–gel matrix and dip-coated onto 316L stainless steel via a mussel-inspired approach followed by AgNP deposition. Benefiting from the synergistic effect of antibacterial AgNP and non-stick PTFE, the AgNP/PTFE coating exhibited superior antibiofilm activity against Escherichia coli WT F1693 and enhanced corrosion resistance. Compared with surfaces only coated with PTFE, the AgNP/PTFE coated surfaces were capable of sustained release of silver ions, inhibiting up to ~50% bacterial biomass accumulation after 7 days. To understand the anti-adhesion mechanism, both classic DLVO and XDLVO theories were used to model and explain bacterial adhesion. Despite concerns that an over-release of silver ions may cause toxic effects towards mammalian cells, the coating procedures offered ease of control over the silver loading, making it potentially useful for preventing metallic implant-associated infections.

YAP in epithelium senses gut barrier loss to deploy defenses against pathogens.

Pathogens commonly disrupt the intestinal epithelial barrier; however, how the epithelial immune system senses the loss of intestinal barrier as a danger signal to activate self-defense is unclear. Through an unbiased approach in the model nematode Caenorhabditis elegans, we found that the EGL-44/TEAD transcription factor and its transcriptional activator YAP-1/YAP (Yes-associated protein) were activated when the intestinal barrier was disrupted by infections with the pathogenic bacterium Pseudomonas aeruginosa PA14. Gene Ontology enrichment analysis of the genes containing the TEAD-binding sites revealed that “innate immune response” and “defense response to Gram-negative bacterium” were two top significantly overrepresented terms. Genetic inactivation of yap-1 and egl-44 significantly reduced the survival rate and promoted bacterial accumulation in worms after bacterial infections. Furthermore, we found that disturbance of the E-cadherin-based adherens junction triggered the nuclear translocation and activation of YAP-1/YAP in the gut of worms. Although YAP is a major downstream effector of the Hippo signaling, our study revealed that the activation of YAP-1/YAP was independent of the Hippo pathway during disruption of intestinal barrier. After screening 10 serine/threonine phosphatases, we identified that PP2A phosphatase was involved in the activation of YAP-1/YAP after intestinal barrier loss induced by bacterial infections. Additionally, our study demonstrated that the function of YAP was evolutionarily conserved in mice. Our study highlights how the intestinal epithelium recognizes the loss of the epithelial barrier as a danger signal to deploy defenses against pathogens, uncovering an immune surveillance program in the intestinal epithelium.

Cumulative hydropathic topology of a voltage-gated sodium channel at atomic resolution.

Voltage-gated sodium channels (NavChs) are biological pores that control the flow of sodium ions through the cell membrane. In humans, mutations in genes encoding NavChs can disrupt physiological cellular activity thus leading to a wide spectrum of diseases. Here, we present a topological connection between the functional architecture of a NavAb bacterial channel and accumulation of atomic hydropathicity around its pore. This connection is established via a scaling analysis methodology that elucidates how intrachannel hydropathic density variations translate into hydropathic dipole field configurations along the pore. Our findings suggest the existence of a nonrandom cumulative hydropathic topology that is organized parallel to the membrane surface so that pore's stability, as well as, gating behavior are guaranteed. Given the biophysical significance of the hydropathic effect, our study seeks to provide a computational framework for studying cumulative hydropathic topological properties of NavChs and pore-forming proteins in general.

Bioaccumulation of Chromium by Autochthonous Bacteria Associated With The Heavy Metal- Resistant Halophyte Arthrocnemum macrostachyum

ARTHROCNEMUM macrostachyum is a halophyte naturally growing on Manzala Lake shoreline of Egypt and able to tolerate and accumulate heavy metals. The use of metal-resistant rhizobacteria is an important technology to improve the tolerance capability of the halophytes in metal-polluted environments. A total of 33 bacterial isolates were obtained from the root system of A. macrostachyum and screened for resistance to 1.25 and 12.5mM of Cr(VI) in plant-based culture medium prepared from the halophyte shoot juice. The six most tolerant isolates were identified based on cell morphology and API microtube profiles. Those isolates were found closely related to Bacillus lentus, Burkholderia cepacia, Raoultella ornithinolytica and Providencia retgeri indicated on the online database. Among the strains tested for their ability to accumulate chromium, Bacillus lentus was the most effective with an average accumulation percentage of 17.8, Providencia retgeri ranked thereafter (15.1%). Bacillus circulance was the least with a negligible accumulation level of 0.5%. The biosorption rate of the heavy metal was contact time- and bacterial strain-dependent. Again, Bacillus lentus showed the highest uptake capacity of 32.8mg g-1, a parameter that positively correlated with contact time (r= 0.865), this was not the case with Burkholderia cepacia where the correlation was negative (r= – 0.811). When introduced into an aqueous solution of 25mg L-1 Cr(VI), Burkholderia cepacia was the superior in Cr(VI) reduction (86.7%), while Bacillus circulance failed to reduce the heavy metal. The pH 5.5 was the most favorable for bacterial Cr accumulation which proportionally decreased as the acidity of the solution increased. This study provides more understanding of the significant contribution of the heavy metal-tolerant microbiome to improve the metal remediation efficiency of halophytic plant covers of stressed environments.

Pretreatment with Scutellaria baicalensis Georgi extract improves the postharvest quality of cut roses (Rosa hybrida L.)

Microbial growth in vase solutions and ethylene damage are often associated with premature senescence in cut flowers. We examined the efficacy of Scutellaria baicalensis Georgi extract (SC) to improve postharvest longevity and quality of two cut roses (Rosa hybrida L.) ‘Jinny’ and ‘Wild Look’ to develop an inexpensive and innocuous preservative solution for the cut flower industry. Pretreatments with 100, 200, 300, and 500 μL L−1 SC effectively extended the vase life of the cut rose cultivars. Among the tested pretreatments, 300 μL L−1 of SC was the most effective concentration and significantly prolonged the postharvest longevity of cut flowers from 11.8 days (control) to 17.4 days in ‘Jinny’ and from 13.6 (control) to 20.9 days in ‘Wild Look’. The beneficial effects of 300 μL L−1 SC pretreatment inhibited bacterial accumulation at the base of the cut stems, enhanced water uptake, and maintained initial fresh weight, positive water balance, and chlorophyll fluorescence (Fv/Fm) in the leaves of cut roses. In addition, 300 μL L−1 SC pretreatment suppressed the transcript levels of ethylene biosynthesis genes (RhACO1, RhACS1, RhACS3, and RhACS4) in rose petals and delayed flower senescence. The efficacy of 300 μL L−1 SC pretreatment in extending the vase life of cut roses was equal to 0.1 mM silver thiosulfate (STS), and greater than hydrosol (H), H + SC, and H + sucrose (H + Suc). Therefore, the results from our study highlight the potential of SC as an alternative preservative in the cut rose industry.

Enantioselective effects of imazethapyr residues on Arabidopsis thaliana metabolic profile and phyllosphere microbial communities

Imazethapyr (IM) is a widely used acetolactate synthase-inhibiting chiral herbicide. It has long-term residuals that may be absorbed by the human body through the edible parts of plants, such as vegetable leaves or fruits. Here, we selected a model plant, Arabidopsis thaliana, to determine the effects of R-IM and S-IM on its leaf structure, photosynthetic efficiency, and metabolites, as well as the structures of microorganisms in the phyllosphere, after 7 days of exposure. Our results indicated enantiomeric differences in plant growth between R-IM and S-IM; 133 µg/kg R-IM showed heavier inhibition of photosynthetic efficiency and greater changes to subcellular structure than S-IM. R-IM and S-IM also had different effects on metabolism and leaf microorganisms. S-IM mainly increased lipid compounds and decreased amino acids, while R-IM increased sugar accumulation. The relative abundance of Moraxellaceae human pathogenic bacteria was increased by R-IM treatment, indicating that R-IM treatment may increase leaf surface pathogenic bacteria. Our research provides a new perspective for evaluating the harmfulness of pesticide residues in soil, phyllosphere microbiome changes via the regulation of plant metabolism, and induced pathogenic bacterial accumulation risks.

Dynamics of pattern formation and emergence of swarming in Caenorhabditis elegans.

Many animals collectively form complex patterns to tackle environmental difficulties. Several biological and physical factors, such as animal motility, population densities, and chemical cues, play significant roles in this process. However, very little is known about how sensory information interplays with these factors and controls the dynamics of pattern formation. Here, we study the direct relation between oxygen sensing, pattern formation, and emergence of swarming in active Caenorhabditis elegans aggregates. We find that when thousands of animals gather on food, bacteria-mediated decrease in oxygen level slows down the animals and triggers motility-induced phase separation. Three coupled factors-bacterial accumulation, aerotaxis, and population density-act together and control the entire dynamics. Furthermore, we find that biofilm-forming bacterial lawns including Bacillus subtilis and Pseudomonas aeruginosa strongly alter the collective dynamics due to the limited diffusibility of bacteria. Additionally, our theoretical model captures behavioral differences resulting from genetic variations and oxygen sensitivity.

How does ultrasonic cavitation remove dental bacterial biofilm?

Bacterial biofilm accumulation is problematic in many areas, leading to biofouling in the marine environment and the food industry, and infections in healthcare. Physical disruption of biofilms has become an important area of research. In dentistry, biofilm removal is essential to maintain health. The aim of this study is to observe biofilm disruption due to cavitation generated by a dental ultrasonic scaler (P5XS, Acteon) using a high speed camera and determine how this is achieved. Streptococcus sanguinis biofilm was grown on Thermanox™ coverslips (Nunc, USA) for 4days. After fixing and staining with crystal violet, biofilm removal was imaged using a high speed camera (AX200, Photron). An ultrasonic scaler tip (tip 10P) was held 2mm away from the biofilm and operated for 2s. Bubble oscillations were observed from high speed image sequences and image analysis was used to track bubble motion and calculate changes in bubble radius and velocity on the surface. The results demonstrate that most of the biofilm disruption occurs through cavitation bubbles contacting the surface within 2s, whether individually or in cavitation clouds. Cleaning occurs through shape oscillating microbubbles on the surface as well as through fluid flow.

Arabinofuranose-derived positron-emission tomography radiotracers for detection of pathogenic microorganisms.

Detection of bacteria-specific metabolism via positron emission tomography (PET) is an emerging strategy to image human pathogens, with dramatic implications for clinical practice. In silico and in vitro screening tools have recently been applied to this problem, with several monosaccharides including l-arabinose showing rapid accumulation in Escherichia coli and other organisms. Our goal for this study was to evaluate several synthetically viable arabinofuranose-derived 18 F analogs for their incorporation into pathogenic bacteria. We synthesized four radiolabeled arabinofuranose-derived sugars: 2-deoxy-2-[18 F]fluoro-arabinofuranoses (d-2-18 F-AF and l-2-18 F-AF) and 5-deoxy-5-[18 F]fluoro-arabinofuranoses (d-5-18 F-AF and l-5-18 F-AF). The arabinofuranoses were synthesized from 18 F- via triflated, peracetylated precursors analogous to the most common radiosynthesis of 2-deoxy-2-[18 F]fluoro-d-glucose ([18 F]FDG). These radiotracers were screened for their uptake into E. coli and Staphylococcus aureus. Subsequently, the sensitivity of d-2-18 F-AF and l-2-18 F-AF to key human pathogens was investigated in vitro. All 18 F radiotracer targets were synthesized in high radiochemical purity. In the screening study, d-2-18 F-AF and l-2-18 F-AF showed greater accumulation in E. coli than in S. aureus. When evaluated in a panel of pathologic microorganisms, both d-2-18 F-AF and l-2-18 F-AF demonstrated sensitivity to most gram-positive and gram-negative bacteria. Arabinofuranose-derived 18 F PET radiotracers can be synthesized with high radiochemical purity. Our study showed absence of bacterial accumulation for 5-substitued analogs, a finding that may have mechanistic implications for related tracers. Both d-2-18 F-AF and l-2-18 F-AF showed sensitivity to most gram-negative and gram-positive organisms. Future in vivo studies will evaluate the diagnostic accuracy of these radiotracers in animal models of infection.

Visualization of Bacterial Resistance using Fluorescent Antibiotic Probes.

Fluorescent antibiotics are multipurpose research tools that are readily used for the study of antimicrobial resistance, due to their significant advantage over other methods. To prepare these probes, azide derivatives of antibiotics are synthesized, then coupled with alkyne-fluorophores using azide-alkyne dipolar cycloaddition by click chemistry. Following purification, the antibiotic activity of the fluorescent antibiotic is tested by minimum inhibitory concentration assessment. In order to study bacterial accumulation, either spectrophotometry or flow cytometry may be used, allowing for much simpler analysis than methods relying on radioactive antibiotic derivatives. Furthermore, confocal microscopy can be used to examine localization within the bacteria, affording valuable information about mode of action and changes that occur in resistant species. The use of fluorescent antibiotic probes in the study of antimicrobial resistance is a powerful method with much potential for future expansion.

Understanding the role of bacterial cellular adsorption, accumulation and bioavailability regulation by biosurfactant in affecting biodegradation efficacy of polybrominated diphenyl ethers

Microbiological degradation is often considered as an important strategy to reduce the risks of polybrominated diphenyl ethers (PBDEs), which are environmentally widespread and harmful to human health and wildlife. With the well-identified aerobic bacteria, i.e. B. xenovorans LB400, the biodegradation of 2,2′,4,4′-tetrabrominated diphenyl ether (BDE-47) occurred efficiently in conformity to the first-order kinetics and showed the strong dependence on initial concentration of pollutant and bioavailability regulation by biosurfactant. The mild increase of initial concentration of BDE-47 would enhance biodegradation whereas the excessive increase failed due to the oxidative stress or cytotoxicity to bacteria. Rather than the bacterial extracellular adsorption that was bioactively-mediated in thermodynamics, the intracellular accumulations at different time gradients showed the negative correlation with biodegradation efficiency of BDE-47. The spontaneous biodegradation of pollutant should be sourced from the gradual reduction of intracellular accumulation. Though the improved bioavailability of BDE-47 by sucrose fatty acid ester (SFAE) hardly altered the extracellular adsorption, the bacterial intracellular accumulation was indicated to increase continuously with used amount of biosurfactant and then decrease for the cellular morphological damage, and interestingly it appeared to be temporary reservoir for prompt delivery to biodegradation in light of the opposite variation tendency with time.

Application of computational fluid dynamics models for the evaluation of salivary flow patterns and related bacterial accumulation around orthodontic brackets.

To simulate and compare salivary flow patterns over a tooth surface bonded with different orthodontic appliances using computational fluid dynamics (CFD) and investigate the impact of bracket design on salivary flow in relation to peri-bracket bacterial accumulation. The models were constructed using computed tomography (CT) data of 81 patients scheduled for fixed orthodontic treatment: 27 patients (10 males, 17 females) for the metal Victory MBT™ bracket; 27 patients (seven males, 20 females) for the ceramic Clarity MBT™ bracket; 27 patients (15 males, 12 females) for the Mini Uni-Twin (MUT) bracket. The salivary flow patterns were simulated by CFD and compared between the groups and the model predictions were validated using a bacteriological experiment. The MUT bracket was associated with the greatest number of low salivary velocity areas, as it is designed with a connector between double tie wings and a right contact angle between tooth surface and bracket base. After archwire placement, the centred slot in the bracket and the bilateral sites around the bracket had higher bacterial retention and needed special oral hygiene measures. The obtuse contact angle of the ceramic bracket formed a pocket structure in the tie-wing area, retarding salivary flow and contributing to bacteria retention. With the evaluation of CFD models, we demonstrate that salivary flow patterns over a tooth surface with a bracket vary with bracket designs and further promote bacterial retention in specific locations, suggesting the need for additional oral hygiene measures for specific bracket types.

Preservative Effects of Gelatin Active Coating Containing Eugenol and Higher CO2 Concentration Modified Atmosphere Packaging on Chinese Sea bass (Lateolabrax maculatus) during Superchilling (-0.9 °C) Storage.

The purpose of this research was to explore the fresh keeping effect of modified atmosphere packaging (MAP) with different gas ratios combined with gelatin active coatings containing eugenol on Chinese sea bass stored at −0.9 °C for 36 days. The results showed that MAP3 (60% CO2/10% O2/30% N2), together with gelatin active coatings containing eugenol, could prevent water loss, which maintained high field NMR, MRI, and organoleptic evaluation results. This hurdle technology could also effectively delay the bacterial reproduction, protein degradation, and alkaline accumulation, so it showed the lowest K value, total volatile basic nitrogen, free amino acids, total viable count, Pseudomonas spp., and H2S-producing bacteria, which better maintain the quality of sea bass.

Distribution of Candidatus Liberibacter asiaticus in Citrus and the Asian Citrus Psyllid in Texas Over a Decade.

Huanglongbing (HLB, citrus greening disease) in the major citrus-producing states of the United States is associated with Candidatus Liberibacter asiaticus (CLas), which is vectored by the Asian citrus psyllid (ACP). Surveys were conducted in Texas from 2007 to 2017 to assess the prevalence and titer of CLas in ACPs and citrus trees. ACP and citrus leaf tissue samples were collected from suspect trees in residential areas and commercial groves (orchards) and assayed for CLas by quantitative PCR. CLas detection in ACPs (2011) preceded that of citrus trees (2012) by several months. Annual incidences of CLas-positive ACPs and leaf tissue followed an exponential growth pattern over the survey period, varying from 0.03 to 28.7% in ACPs and 0.6 to 36.5% in citrus trees. There was a significant and positive relationship between the monthly incidences of CLas-positive ACP and leaf tissue samples. The proportion of HLB detection sites also increased with time, reaching 26 and 40% of commercial groves and residential sites, respectively, by 2017. Seasonal variations were observed in the incidences of CLas-positive ACPs and citrus trees such that significantly more CLas-positive ACPs and trees were recorded during the fall and winter of a given year relative to the hot summer. A temporal analysis of the class distribution of cycle threshold values revealed a trend of increased bacterial accumulation in ACPs and trees over time, with the trend more pronounced for the former than the latter host type. These findings provide a comprehensive insight into the ongoing CLas/HLB epidemic in Texas, with potential lessons for California and other citrus-producing areas where the disease is not yet established.

Relationship between Polishing Techniques and Bacterial Count on Different Denture Base Materials

Introduction: Wearing of dentures cause alteration in the oral microflora and increasing in number of bacteria and candida. The polished and fitting surfaces of the denture are both affected. Different polishing techniques influence the total count of bacterial accumulation on the denture surface. Aim: To count the bacterial colonies after polishing three denture base materials before and after six months of denture wearing by different polishing techniques. Materials and Method: Eighteen patients were randomly selected for construction of maxillary partial denture. They were divided into 3 groups: Group 1: Patients received conventional heat-cured PMMA (Acrostone) denture. Group 2: Patients received thermoformed polyamide (NEWULTRA) denture. Group 3: Patients received thermoformed acetal (Bio Dentaplast) denture. In each group, three patients had their dentures polished by pre polishing with brown rubber disc and fine pumice with wet rag wheel, and the other three patients with the same technique but followed by tripoli compound with dry rag wheel. Evaluation of bacterial counting was conducted before denture wearing and after six months of denture wearing. Swabs were taken from the palate of the patients and bacteria were counted. Findings: No significant difference was found between technique no. I and no. II in decreasing the bacterial count between the tested materials. Thermoformed polyamide showed the highest bacterial count after six months of wearing denture polished by technique no. II followed by thermoformed acetal and heat-cured PMMA. Conclusion: The second polishing technique produced less surface roughness and bacterial colonization on the tested materials than the first one.

Platform switching implant

For the implant to function successfully, there should be a good integration between implant, hard, and soft tissue. The implant should be able to provide esthetics, good functioning of the masticatory muscles, phonetics, and above all to minimize the crestal bone loss and hence maintaining the crestal bone levels. Over the recent years, as compared to traditional implants which resulted in bacterial accumulation, inflammatory cell infiltrate and violation of biologic width and thus bone loss and hence compromising implant integrity, platform switching implants have proved to be better option in maintain crestal bone levels by keeping the inflammatory infiltrate away from the crestal bone, allowing horizontal and vertical extension of biologic width, equalize the distribution of stress to centre of implant and ultimately can help to preserve the crestal bone levels. Keywords: Platform switching, Biologic width, Crestal bone, Inflammatory infiltrate, Traditional implants.

Numerical investigation of cavitation generated by an ultrasonic dental scaler tip vibrating in a compressible liquid.

Bacterial biofilm accumulation around dental implants is a significant problem leading to peri-implant diseases and implant failure. Cavitation occurring in the cooling water around ultrasonic scaler tips can be used as a novel solution to remove debris without any surface damage. However, current clinically available instruments provide insufficient cavitation around the activated tip surface. To solve this problem a critical understanding of the vibro-acoustic behaviour of the scaler tip and the associated cavitation dynamics is necessary. In this research, we carried out a numerical study for an ultrasound dental scaler with a curved shape tip vibrating in water, using ABAQUS based on the finite element method. We simulated the three-dimensional, nonlinear and transient interaction between the vibration and deformation of the scaler tip, the water flow around the scaler and the cavitation formation and dynamics. The numerical model was well validated with the experiments and there was excellent agreement for displacement at the free end of the scaler. A systematic parametric study has been carried out for the cavitation volume around the scaler tip in terms of the frequency, amplitude and power of the tip vibration. The numerical results indicate that the amount of cavitation around the scaler tip increases with the frequency and amplitude of the vibration. However, if the frequency is far from the natural frequency, the cavitation volume around the free end decreases due to reduced free end vibration amplitude.

Clogging evolution in porous media under the coexistence of suspended particles and bacteria: Insights into the mechanisms and implications for groundwater recharge

Artificial recharge of groundwater is an effective strategy for supplementing groundwater resources. It is noteworthy that most artificial recharge facilities suffer from clogging problems, which mainly result from suspended particles or bacteria in the recharge water. In this study, percolation experiments in sand columns were used to investigate the combined effects of suspended particles and bacteria on the permeability of porous media, which has been ignored in the past. During the recharge process, it took a much shorter period of time (3 h) for a particle-bacteria group (PBG) to achieve a relative hydraulic conductivity of 0.30 compared with a particle-only group (PG) (28 h) and a bacteria-only group (BG) (3.5 h). A combination of relevance analysis, pathway analysis, electron microscopy, and high-throughput sequencing were employed to identify the key controlling factors in the occurrence of clogging and the governing mechanisms under the co-existence of particles and bacteria. The dominant genera of the PBG included Acinetobacter, Sphingobacterium, Comamonas and Elizabethkingia. These microbes displayed a poor ability for movement and high adhesion, which facilitated the clogging process for the PBG. The results indicated that bacterial cell growth and particle accumulation contributed to a reduction in K’ both separately and interactively during the recharge process (0–3 h), but that polysaccharide produced by bacteria began to have an impact during the later stages (stage II: 0.5–1 h and stage III: 1–3 h). The development of clogging in the PBG was primarily controlled by van der Waals forces, electrostatic repulsion and bridging during stage I (0–0.5 h). During the later stages, hydrogen bonds and polymerization of extracellular polymeric substances became the governing factors. These results provide an evaluation of clogging under the coexistence of suspended particles and bacteria, having implications for field-based artificial recharge.