Penetration and Accumulation of Dendrons with Different Peripheral Composition in Pseudomonas aeruginosa Biofilms.
ABSTRACT: Multidrug resistant bacterial infections threaten to become the number one cause of death by the year 2050. Development of antimicrobial dendritic polymers is considered promising as an alternative infection control strategy. For antimicrobial dendritic polymers to effectively kill bacteria residing in infectious biofilms, they have to penetrate and accumulate deep into biofilms. Biofilms are often recalcitrant to antimicrobial penetration and accumulation. Therefore, this work aims to determine the role of compact dendrons with different peripheral composition in their penetration into Pseudomonas aeruginosa biofilms. Red fluorescently labeled dendrons with pH-responsive NH3+ peripheral groups initially penetrated faster from a buffer suspension at pH 7.0 into the acidic environment of P. aeruginosa biofilms than dendrons with OH or COO- groups at their periphery. In addition, dendrons with NH3+ peripheral groups accumulated near the top of the biofilm due to electrostatic double-layer attraction with negatively charged biofilm components. However, accumulation of dendrons with OH and COO- peripheral groups was more evenly distributed across the depth of the biofilms than NH3+ composed dendrons and exceeded accumulation of NH3+ composed dendrons after 10 min of exposure. Unlike dendrons with NH3+ groups at their periphery, dendrons with OH or COO- peripheral groups, lacking strong electrostatic double-layer attraction with biofilm components, were largely washed-out during exposure to PBS without dendrons. Thus, penetration and accumulation of dendrons into biofilms is controlled by their peripheral composition through electrostatic double-layer interactions, which is an important finding for the further development of new antimicrobial or antimicrobial-carrying dendritic polymers.
Project description:The utilization of cellulose in industrial applicat is of great significance to sustainable development of human society and reducing dependence on dwindling fossil resources. Nevertheless, this utilization of cellulose has actually been limited due to its insolubilization. Here, novel solvents consisting of diallylimidazolium methoxy acetate ([A<sub>2</sub>im][CH<sub>3</sub>OCH<sub>2</sub>COO]) and N-methylpyrrolidinone (NMP) were developed. The solubility of cellulose in [A<sub>2</sub>im][CH<sub>3</sub>OCH<sub>2</sub>COO]/NMP was determined, and the influence of [A<sub>2</sub>im][CH<sub>3</sub>OCH<sub>2</sub>COO]/NMP molar ratio on cellulose dissolution was systematically investigated. Meanwhile, we also presented the affecting factors of the cellulose material fabrication including preparation approach, [A<sub>2</sub>im][CH<sub>3</sub>OCH<sub>2</sub>COO] and cellulose solution concentration. Attractively, the [A<sub>2</sub>im][CH<sub>3</sub>OCH<sub>2</sub>COO]/NMP solvents display much powerful dissolution capacity for cellulose even at 25?°C (25.4?g 100?g<sup>-1</sup>). This is mainly ascribed to the combined factors: The hydrogen bond interactions of the H2, H4 and H6 in [A<sub>2</sub>im]<sup>+</sup> and carboxyl O atom in [CH<sub>3</sub>OCH<sub>2</sub>COO]<sup>-</sup> with the hydroxyl H atom and O atom in cellulose; the dissociation of NMP towards [A<sub>2</sub>im][CH<sub>3</sub>OCH<sub>2</sub>COO]; the stabilization of NMP towards the dissolved cellulose chains. In addition, the thermostability and chemical structure of the regenerated cellulose from the solvents was also estimated.
Project description:Direct electrolytic N<sub>2</sub> reduction to ammonia (NH<sub>3</sub>) is a renewable alternative to the Haber-Bosch process. The activity and selectivity of electrocatalysts are evaluated by measuring the amount of NH<sub>3</sub> in the electrolyte. Quantitative <sup>1</sup>H nuclear magnetic resonance (qNMR) detection reduces the bench time to analyze samples of NH<sub>3</sub> (present in the assay as NH<sub>4</sub> <sup>+</sup>) compared to conventional spectrophotometric methods. However, many groups do not have access to an NMR spectrometer with sufficiently high sensitivity. We report that by adding 1 mM paramagnetic Gd<sup>3+</sup> ions to the NMR sample, the required analysis time can be reduced by an order of magnitude such that fast NH<sub>4</sub> <sup>+</sup> detection becomes accessible with a standard NMR spectrometer. Accurate, internally calibrated quantification is possible over a wide pH range.
Project description:Catecholamines participate in angiogenesis, an important tumor development process. However, the way catecholamines interact with their receptors has not been completely elucidated, and doubts still remain as to whether these interactions occur between catechol and/or amine sites and particular amino acid residues on the catecholamine receptors. To evaluate how catechol and amine groups contribute to angiogenesis, we immobilized the catechol site through ruthenium ion (Ru) coordination, to obtain species with the general formula [Ru(NH<sub>3</sub>)<sub>4</sub>(catecholamine-R)]Cl. We then assessed the angiogenic activity of the complexes in a chorioallantoic membrane model (CAM) and examined vascular reactivity and calcium mobilization in rat aortas and vascular cells. [Ru(NH<sub>3</sub>)<sub>4</sub>(catecholamine-R)]Cl acted as partial agonists and/or antagonists of their respective receptors and induced calcium mobilization. [Ru(NH<sub>3</sub>)<sub>4</sub>(isoproterenol)]<sup>+</sup> [Ru(NH<sub>3</sub>)<sub>4</sub>(noradrenaline)]<sup>+</sup>, and [Ru(NH<sub>3</sub>)<sub>4</sub>(adrenaline)]<sup>+</sup> behaved as antiangiogenic complexes, whereas [Ru(NH<sub>3</sub>)<sub>4</sub>(dopamine)]<sup>+</sup> proved to be a proangiogenic complex. In conclusion, catecholamines and [Ru(NH<sub>3</sub>)<sub>4</sub>(catecholamine-R)]Cl can modulate angiogenesis, and catechol group availability can modify the way these complexes impact the vascular tone, suggesting that catecholamines and their receptors interact differently after catecholamine coordination to ruthenium.
Project description:Nitrogen (N) is a limiting nutrient in vast regions of the world's oceans, yet the sources of N available to various phytoplankton groups remain poorly understood. In this study, we investigated inorganic carbon (C) fixation rates and nitrate (NO<sub>3</sub><sup>-</sup>), ammonium (NH<sub>4</sub><sup>+</sup>) and urea uptake rates at the single cell level in photosynthetic pico-eukaryotes (PPE) and the cyanobacteria Prochlorococcus and Synechococcus. To that end, we used dual <sup>15</sup>N and <sup>13</sup>C-labeled incubation assays coupled to flow cytometry cell sorting and nanoSIMS analysis on samples collected in the North Pacific Subtropical Gyre (NPSG) and in the California Current System (CCS). Based on these analyses, we found that photosynthetic growth rates (based on C fixation) of PPE were higher in the CCS than in the NSPG, while the opposite was observed for Prochlorococcus. Reduced forms of N (NH<sub>4</sub><sup>+</sup> and urea) accounted for the majority of N acquisition for all the groups studied. NO<sub>3</sub><sup>-</sup> represented a reduced fraction of total N uptake in all groups but was higher in PPE (17.4?±?11.2% on average) than in Prochlorococcus and Synechococcus (4.5?±?6.5 and 2.9?±?2.1% on average, respectively). This may in part explain the contrasting biogeography of these picoplankton groups. Moreover, single cell analyses reveal that cell-to-cell heterogeneity within picoplankton groups was significantly greater for NO<sub>3</sub><sup>-</sup> uptake than for C fixation and NH<sub>4</sub><sup>+</sup> uptake. We hypothesize that cellular heterogeneity in NO<sub>3</sub><sup>-</sup> uptake within groups facilitates adaptation to the fluctuating availability of NO<sub>3</sub><sup>-</sup> in the environment.
Project description:This article illustrates the detailed decomposition behavior of NH<sub>4</sub>HSO<sub>4</sub> on the TiO<sub>2</sub> and TiO<sub>2</sub>-SiO<sub>2</sub> supports, along with the effect of SiO<sub>2</sub> addition on the sulfur resistance of the corresponding V<sub>2</sub>O<sub>5</sub>-based catalysts. For TiO<sub>2</sub> support, sulfate species selectively occupied its surface basic hydroxyl groups, while Si-OH groups functioned as the main sites for the accommodation of NH<sub>4</sub>HSO<sub>4</sub> over the TiO<sub>2</sub>-SiO<sub>2</sub> mixed support, enabling its surface sulfate species with higher thermal stability. Compared with NH<sub>4</sub> <sup>+</sup> on the TiO<sub>2</sub> surface, NH<sub>4</sub> <sup>+</sup> on the TiO<sub>2</sub>-SiO<sub>2</sub> mixed support was much easier to be consumed during the heating process, hence causing some variations in the decomposition behavior of NH<sub>4</sub>HSO<sub>4</sub>. Finally, adding SiO<sub>2</sub> enhanced the SO<sub>2</sub> tolerance properties of the catalysts to a certain extent. When exposed to the SO<sub>2</sub>-containing flue gas, the deposition of NH<sub>4</sub>HSO<sub>4</sub> mainly caused serious deactivation of SiO<sub>2</sub>-free catalyst, while the as-accumulated SO<sub>4</sub> <sup>2-</sup> also contributed to the declined activity of SiO<sub>2</sub>-added catalyst. These results ensured the potential commercialization of TiO<sub>2</sub>-SiO<sub>2</sub>-based catalysts in the typical low-temperature selective catalytic reduction systems in the short run and pointed out a strategy to design new catalysts with superior activity and enhanced SO<sub>2</sub>-tolerant ability.
Project description:Understanding the structural dynamics of lead-halide perovskites is essential for their advanced use as photovoltaics. Here, the structural dynamics of the CH<sub>3</sub>NH<sub>3</sub> cation and PbBr<sub>6</sub> octahedra in the perovskite CH<sub>3</sub>NH<sub>3</sub>PbBr<sub>3</sub> were studied via nuclear magnetic resonance (NMR) to determine the mechanism of the transition from the tetragonal to cubic phase. The chemical shifts were obtained by <sup>1</sup>H, <sup>13</sup>C, and <sup>207</sup>Pb magic angle spinning NMR and <sup>14</sup>N static NMR. The chemical shifts of the <sup>1</sup>H nuclei in CH<sub>3</sub> and NH<sub>3</sub> remained constant with increasing temperature, whereas those of the <sup>13</sup>C and <sup>207</sup>Pb nuclei varied near the phase transition temperature (T<sub>C</sub>?=?236 K), indicating that the structural environments of <sup>13</sup>C and <sup>207</sup>Pb change near T<sub>C</sub>. The spin-lattice relaxation time T<sub>1?</sub> values for <sup>1</sup>H, <sup>13</sup>C, and <sup>207</sup>Pb nuclei increased with increasing temperature and did not exhibit an abrupt change near T<sub>C</sub>. In addition, the two lines in the <sup>14</sup>N NMR spectra superposed into one line near T<sub>C</sub>, indicating the occurrence of a phase transition to a cubic phase with higher symmetry than tetragonal. Consequently, the main factor causing the phase transition from the tetragonal to cubic phase near T<sub>C</sub> is a change in the surroundings of the <sup>207</sup>Pb nuclei in the PbBr<sub>6</sub> octahedra and of the C-N groups in the CH<sub>3</sub>NH<sub>3</sub> cations.
Project description:Autotrophic nitrogen removal by anaerobic ammonium oxidizing (anammox) bacteria is an energy-efficient nitrogen removal process in wastewater treatment. However, full-scale deployment under mainstream conditions remains challenging for practitioners due to the high stress susceptibility of anammox bacteria towards fluctuations in dissolved oxygen (DO) and temperature. Here, we investigated the response of microbial biofilms with verified anammox activity to DO shocks under 20?°C and 14?°C. While pulse disturbances of 0.3?mg?L<sup>-1</sup> DO prompted only moderate declines in the NH<sub>4</sub><sup>+</sup> removal rates, 1.0?mg?L<sup>-1</sup> DO led to complete but reversible inhibition of the NH<sub>4</sub><sup>+</sup> removal activity in all reactors. Genome-centric metagenomics and metatranscriptomics were used to investigate the stress response on various biological levels. We show that temperature regime and strength of DO perturbations induced divergent responses from the process level down to the transcriptional profile of individual taxa. Community-wide gene expression differed significantly depending on the temperature regime in all reactors, and we found a noticeable impact of DO disturbances on genes involved in transcription, translation, replication and posttranslational modification at 20?°C but not 14?°C. Genome-centric analysis revealed that different anammox species and other key biofilm taxa differed in their transcriptional responses to distinct temperature regimes and DO disturbances.
Project description:Biofilm-related infections can develop everywhere in the human body and are rarely cleared by the host immune system. Moreover, biofilms are often tolerant to antimicrobials, due to a combination of inherent properties of bacteria in their adhering, biofilm mode of growth and poor physical penetration of antimicrobials through biofilms. Current understanding of biofilm recalcitrance toward antimicrobial penetration is based on qualitative descriptions of biofilms. Here we hypothesize that stress relaxation of biofilms will relate with antimicrobial penetration. Stress relaxation analysis of single-species oral biofilms grown in vitro identified a fast, intermediate and slow response to an induced deformation, corresponding with outflow of water and extracellular polymeric substances, and bacterial re-arrangement, respectively. Penetration of chlorhexidine into these biofilms increased with increasing relative importance of the slow and decreasing importance of the fast relaxation element. Involvement of slow relaxation elements suggests that biofilm structures allowing extensive bacterial re-arrangement after deformation are more open, allowing better antimicrobial penetration. Involvement of fast relaxation elements suggests that water dilutes the antimicrobial upon penetration to an ineffective concentration in deeper layers of the biofilm. Next, we collected biofilms formed in intra-oral collection devices bonded to the buccal surfaces of the maxillary first molars of human volunteers. Ex situ chlorhexidine penetration into two weeks old in vivo formed biofilms followed a similar dependence on the importance of the fast and slow relaxation elements as observed for in vitro formed biofilms. This study demonstrates that biofilm properties can be derived that quantitatively explain antimicrobial penetration into a biofilm.
Project description:<h4>Background</h4>Carbapenemase-producing <i>Enterobacteriaceae</i> (CPE) pose a considerable threat to modern medicine. New treatment options and methods to limit spread need to be investigated. Blue light (BL) is intrinsically antimicrobial, and we have previously demonstrated significant antimicrobial effects on biofilms of a panel of isolates, including two CPEs.This study was performed to assess the antibacterial activity of 405?nm BL against a panel of CPE isolates (four encoding <i>bla</i> <sub>NDM</sub>, three <i>bla</i> <sub>KPC</sub>, two <i>bla</i> <sub>OXA-48</sub>, and three encoding both NDM and OXA-48 carbapenemases).<h4>Methods</h4>In vitro experiments were conducted on 72?h old biofilms of CPEs which were exposed to 60?mW/cm<sup>2</sup> of BL. Changes to biofilm seeding were assessed by measuring the optical density of treated and untreated biofilms.<h4>Results</h4>Twelve bacterial clinical isolates (comprising eight <i>Klebsiella pnemoniae</i>, one <i>K. oxytoca</i>, and three <i>Escherichia coli</i>) were tested. BL was delivered for 5, 15 and 30?min, achieving doses of 162, 54, and 108?J/cm<sup>2</sup>, respectively.All of the CPEs were susceptible to BL treatment, with increasing reductions in seeding with increasing durations of exposure. At 30?min, reductions in biofilm seeding of ?80% were observed for 11 of the 12 isolates, compared to five of 12 after 15?min. CPE_8180 was less susceptible than the rest, with a maximum reduction in seeding of 66% at 30?min.<h4>Conclusions</h4>BL is effective at reducing the seeding of mature CPE biofilms in vitro, and offers great promise as a topical decontamination/treatment agent for both clinical and environmental applications.
Project description:Six species of phytoplankton recently isolated from upper San Francisco Bay were tested for their sensitivity to growth inhibition by ammonium (NH<sub>4</sub><sup>+</sup> ), and for differences in growth rates according to inorganic nitrogen (N) growth source. The quantum yield of photosystem II (F<sub>v</sub> /F<sub>m</sub> ) was a sensitive indicator of NH<sub>4</sub><sup>+</sup> toxicity, manifested by a suppression of F<sub>v</sub> /F<sub>m</sub> in a dose-dependent manner. Two chlorophytes were the least sensitive to NH<sub>4</sub><sup>+</sup> inhibition, at concentrations of >3,000 ?moles NH<sub>4</sub><sup>+</sup> · L<sup>-1</sup> , followed by two estuarine diatoms that were sensitive at concentrations >1,000 ?moles NH<sub>4</sub><sup>+</sup> · L<sup>-1</sup> , followed lastly by two freshwater diatoms that were sensitive at concentrations between 200 and 500 ?moles NH<sub>4</sub><sup>+</sup> · L<sup>-1</sup> . At non-inhibiting concentrations of NH<sub>4</sub><sup>+</sup> , the freshwater diatom species grew fastest, followed by the estuarine diatoms, while the chlorophytes grew slowest. Variations in growth rates with N source did not follow taxonomic divisions. Of the two chlorophytes, one grew significantly faster on nitrate (NO<sub>3</sub><sup>-</sup> ), whereas the other grew significantly faster on NH<sub>4</sub><sup>+</sup> . All four diatoms tested grew faster on NH<sub>4</sub><sup>+</sup> compared with NO<sub>3</sub><sup>-</sup> . We showed that in cases where growth rates were faster on NH<sub>4</sub><sup>+</sup> than they were on NO<sub>3</sub><sup>-</sup> , the difference was not larger for chlorophytes compared with diatoms. This holds true for comparisons across a number of culture investigations suggesting that diatoms as a group will not be at a competitive disadvantage under natural conditions when NH<sub>4</sub><sup>+</sup> dominates the total N pool and they will also not have a growth advantage when NO<sub>3</sub><sup>-</sup> is dominant, as long as N concentrations are sufficient.