Have flagella a preferred orientation during early stages of biofilm formation?: AFM study using patterned substrates

Biofilm development involves several stages and flagellar expression of bacteria is considered an important factor in this process. However, its role in the earliest stage of biofilm development is not yet clear. In order to analyse this topic, Pseudomonas fluorescens samples were trapped on a patterned gold surface with sub-microtrenches (ST) so as to hinder their motility, and nanostructured gold with random orientation (SR) was used as control substrate. Atomic force microscopic (AFM) observations were made on untreated samples. Initially, ca. 75% of the flagella on ST and 85% of flagella on SR are oriented towards the neighbouring bacteria. Some of them made contact and surrounded the cells. Subsequently, 2-D raft structures formed on SR inert substrates with lateral curly flagella, while those at the poles of the rafts turned towards the nearest cell group. A few flagella and the formation of 3-D bacterial structures were observed on toxic substrates like copper. Results showed that patterned substrates are suitable tools to detect the orientation of flagella in the earliest stage of biofilm formation on solid opaque surfaces avoiding sample pre-treatment.     

A multifunctional micro-fluidic system for dielectrophoretic concentration coupled with immuno-capture of low numbers of Listeria monocytogenes

In this study, we demonstrated a micro-fluidic system with multiple functions, including concentration of bacteria using dielectrophoresis (DEP) and selective capture using antibody recognition, resulting in a high capture efficiency of bacterial cells. The device consisted of an array of oxide covered interdigitated electrodes on a flat silicon substrate and a approximately 16 microm high and approximately 260 microm wide micro-channel within a PDMS cover. For selective capture of Listeria monocytogenes from the samples, the channel surface was functionalized with a biotinylated BSA-streptavidin-biotinylated monoclonal antibody sandwich structure. Positive DEP (at 20 V(pp) and 1 MHz) was used to concentrate bacterial cells from the fluid flow. DEP could collect approximately 90% of the cells in a continuous flow at a flow rate of 0.2 microl min(-1) into the micro-channel with concentration factors between 10(2)-10(3), in sample volumes of 5-20 microl. A high flow rate of 0.6 microl min(-1) reduced the DEP capture efficiency to approximately 65%. Positive DEP attracts cells to the edges of the electrodes where the field gradient is the highest. Cells concentrated by DEP were captured by the antibodies immobilized on the channel surface with efficiencies of 18 to 27% with bacterial cell numbers ranging from 10(1) to 10(3) cells. It was found that DEP operation in our experiments did not cause any irreversible damage to bacterial cells in terms of cell viability. In addition, increased antigen expression (antigens to C11E9 monoclonal antibody) on cell membranes was observed following the exposure to DEP.     

Evolution of hydrocarbons and bacterial activity in the marine sediments contaminated by crude oil overflow and treated

The fate of an experimental oil pollution of intertidal sediments in a sheltered beach of North Brittany (France) has been investigated over a 16-month period. Chemical treatments were applied to two of the three contaminated plots by pre-mixing oil respectively with dispersant and biodegrading agents. The physico-chemical and bacteriological characteristics of the polluted areas were followed with the purpose of identifying the limiting parameters for oil microbial degradation and the effect of treatment. The concentration of hydrocarbons in the oiled sediments did not change significantly during the experimental period. Spectrofluorimetric and chromatographic data showed that the main evolution of oil concerns the degradation of n-alkanes and the removal of light aromatics. Biodegradation of hydrocarbons occurred at a measurable rate only during the warm seasons (average temperature 18 +/- 2 degrees C) causing after sixteen months the disappearance of more than 80% of the n-alkanes fraction independently of the pollution sediment level and the chemical treatment of the experimental plots. However, the biodegradation of n-alkanes proceeded during the first months, at different rates, inversely depending on oil content in the collected samples. The main limiting factor is dissolved oxygen according to the fact that spilled oil was located at 3-5 cm depth in a poorly oxygenated zone characterized by low redox potential. Nutrients were not a limiting factor probably due to domestic and agricultural inputs in this area. A marked bacterial growth was observed two weeks after the oil spill with a relative increase in hydrocarbon degrading bacteria with respect to total heterotrophs. Degradation rates, based on C14 n-hexadecane experiments, seem to follow the same way than specific bacterial counts (plate technique). Specific bacteria are always high at the end of our 16 months' field experimentation. In the laboratory as well as in the field experiments, the same behaviour of untreated and chemically treated oil was observed in partially anaerobic sediment.     

Solar Ultraviolet Radiation Exposure and Sun Protection Behaviors and Knowledge Among a High‐Risk and Overlooked Group of Outdoor Workers in South Africa

The exposure of outdoor car guards to solar ultraviolet radiation (UVR), the majority with deeply pigmented skin, to solar UVR was measured for five consecutive days during early spring (September 2017) in South Africa using electronic UVR dosimeters attached to the upper arm of each participant. The exposure of the nape of the neck, forehead, nose, cheek and hand was extrapolated from the measurements. The onsite ambient solar UVR on a flat, horizontal, unshaded surface was measured concurrently. The sun‐related knowledge, behavior and attitudes of the car guards were evaluated using questionnaires. Total personal daily solar UVR exposure as a percentage of the ambient solar UVR exposure was 24%. The exposure of car guards on several body sites was in excess of the occupational threshold limit value. Sleeved shirts and hats were the most commonly used sun protection measures (worn by 70% and 80%, respectively). Considering the high levels of solar UVR reported on most days throughout the year in South Africa, more studies quantifying the personal exposure of outdoor workers in both the informal and formal sectors are necessary.     

Facile preparation and characterization of highly antimicrobial colloid Ag or Au nanoparticles

A series of colloid silver or gold nanoparticles (AgNPs or AuNPs) were successfully prepared by in situ reduction and stabilization of hyperbranched poly(amidoamine) with terminal dimethylamine groups (HPAMAM-N(CH(3))(2)) in water, and they all exhibited highly antimicrobial activity. The particle size could be controlled easily by adjusting the molar ratio of N/Ag (or N/Au) in feed. When the molar ratio was 2, some aggregates of the nanoparticles separated from the colloidal solution, which showed some limited antimicrobial activity with the bacterial inhibition ratio of below 15%. As the molar ratio increased from 10 to 30, the average particle diameters decreased (from ca. 7.1 to 1.0 nm for AgNPs and from ca. 7.7 to 3.9 nm for AuNPs, respectively) and they all showed high dispersion stability and excellent antimicrobial efficiency. All the bacterial inhibition ratios reached up to ca. 98% at the low silver content of ca. 2.0 microg/mL or at the low gold content of ca. 2.8 microg/mL. The AgNPs or AuNPs with smaller particle size can provide much more effective contact surface with the bacteria, thus enhancing their antimicrobial efficiency. Besides, the cationic HPAMAM-N(CH(3))(2) can also do some contribution to the antimicrobial activity through the strong ionic interaction with the bacteria.     

Role of Transition Metals in UV‐B‐Induced Damage to Bacteria

The purpose of this study was to explore the possible link between metals and UV‐B‐induced damage in bacteria. The effect of growth in the presence of enhanced concentrations of different transition metals (Co, Cu, Fe, Mn and Zn) on the UV‐B sensitivity of a set of bacterial isolates was explored in terms of survival, activity and oxidative stress biomarkers (ROS generation, damage to DNA, lipid and proteins and activity of antioxidant enzymes). Metal amendment, particularly Fe, Cu and Mn, enhanced bacterial inactivation during irradiation by up to 35.8%. Amendment with Fe increased ROS generation during irradiation by 1.2–13.3%, DNA damage by 10.8–37.4% and lipid oxidative damage by 9.6–68.7%. Lipid damage during irradiation also increased after incubation with Cu and Co by up to 66.8% and 56.5% respectively. Mn amendment decreased protein carbonylation during irradiation by up to 44.2%. These results suggest a role of Fe, Co, Cu and Mn in UV‐B‐induced bacterial inactivation and the importance of metal homeostasis to limit the detrimental effects of ROS generated during irradiation.     

Raman spectroscopic identification of single bacterial cells at different stages of their lifecycle

Early, rapid, and reliable bacterial identification is of great importance in natural environments and in medical situations. Numerous studies have shown that Raman spectroscopy can be used to differentiate between different bacteria under controlled laboratory conditions. However, individual bacteria within a population exhibit macromolecular and metabolic heterogeneity over their lifetime. Therefore it is important to be able to identify and classify specific bacteria at different time points of the growth cycle. In this study, four species of bacteria were used to explore the capability of confocal Raman spectroscopy as a tool for the identification of (and discrimination between) diverse bacterial species at various growth time points. The results show that bacterial cells from different growth time points (as well as from a random growth phase) can be discriminated among the four species using principal component analysis (PCA). The results also show that bacteria selected from different growth phases can be classified with the help of a prediction model based on principal component and linear discriminant analysis (PC-LDA). These findings demonstrate that Raman spectroscopy with the application of a PC-LDA model rooted in chemotaxonomic analysis has potential for rapid sensing of microbial cells in environmental and clinical studies.     

Effect of UVR on Lake Water and Macrophyte Leachates in Shallow Andean-Patagonian Lakes: Bacterial Response to Changes in Optical Features

The aim of this study was to identify bacterial responses in two shallow lakes from Patagonia to UV-irradiated dissolved organic matter (DOM) coming from different sources. We carried out laboratory experiments in which natural lake water and Potamogeton linguatus leachates were irradiated (UVA-340 fluorescent tubes Q-Panel) or kept in darkness. Natural bacterial assemblages were then incubated in four treatments: natural lake water, irradiated lake water, macrophyte leachate and irradiated macrophyte leachate. We estimated bacterial abundance, composition and activity, and changes in the optical features of DOM. Our results showed that the addition of leachates caused an increase in the DOM mean molecular size. After UV exposure, a high bacterial activity was observed in lake water treatments. On the contrary, carbon uptake by bacteria was reduced in the irradiated leachate treatment. The degree of aromatization in the leachate treatments increased and thus may contribute to a dissolved carbon less available for bacterial activity. Regarding the bacteria assemblage we observed that β -Proteobacteria outcompete the other groups in the leachate treatments, this group being more efficient at utilizing the high molecular weight DOM. These results highlight the importance of UVR interacting with different DOM sources in bacteria responses of shallow lakes.     

Interaction forces between waterborne bacteria and activated carbon particles

Activated carbons remove waterborne bacteria from potable water systems through attractive Lifshitz-van der Waals forces despite electrostatic repulsion between negatively charged cells and carbon surfaces. In this paper we quantify the interaction forces between bacteria with negatively and positively charged, mesoporous wood-based carbons, as well as with a microporous coconut carbon. To this end, we glued carbon particles to the cantilever of an atomic force microscope and measured the interaction forces upon approach and retraction of thus made tips. Waterborne Raoultella terrigena and Escherichia coli adhered weakly (1-2 nN) to different activated carbon particles, and the main difference between the activated carbons was the percentage of curves with attractive sites revealed upon traversing of a carbon particle through the bacterial EPS layer. The percentage of curves showing adhesion forces upon retraction varied between 21% and 69%, and was highest for R. terrigena with positively charged carbon (66%) and a coconut carbon (69%). Macroscopic bacterial removal by the mesoporous carbon particles increased with increasing percentages of attractive sites revealed upon traversing a carbon particle through the outer bacterial surface layer.     

Volatilization of Pesticides from Plant and Soil Surfaces—Field Versus Laboratory Experiments

Abstract

Comparative volatilization experiments were carried out using isoproturon and parathion-methyl sprayed on French beans in field experiments and on plant stands (0.5 m²) in the volatilization chamber developed by the SLFA Neustadt using both compounds ¹⁴C-labelled. The experimental conditions in the field experiments concerning wind speed, temperature and humidity fluctuations were simulated in the volatilization chamber. The laboratory experiment reflected the actual outdoor situation, showing only a negligible amount of volatile isoproturon directly measured in air samples, and providing no reduction of the A.I. residues in plants compared with the initial value in the corresponding field experiment. 77.2% of the parathion-methyl applied to the plants were volatilized and measured directly in air samples in the volatilization chamber while a reduction by 74.7% was found for the corresponding field experiment by residue analysis of the plants after 24 h. No details could be given concerning the nature of the evaporated portions in the field experiment.     

The role of phosphate in bacterial interaction with iron-coated surfaces

This study investigated the role of phosphate in the adhesion of bacteria (Staphylococcus aureus ATCC 10537) to iron-coated surfaces. Column experiments were performed at phosphate concentrations ranging from 0.0 to 2.0 mM. Bacterial breakthrough curves were obtained by monitoring effluent, and mass recovery and sticking efficiency were quantified from these curves. At phosphate concentrations between 0 and 0.5 mM, bacterial attachment to iron-coated sand decreased with increasing phosphate concentration (mass recovery increased from 14.0 to 86.3%), possibly due to charge modification of the coated sand from positive to negative by adsorbed phosphate ions. Between 0.5 and 2.0 mM, however, bacterial attachment increased with increasing phosphate concentration (mass recovery decreased from 86.3 to 41.3%), possibly due to compression of the electrical double layer between bacteria and phosphate-adsorbed/negatively charged surfaces by free phosphate ions. This study demonstrates that phosphate can play different roles in bacterial interaction with iron-coated surfaces depending on its concentration.     

Bacterial attachment to iron-impregnated granular activated carbon

Bacterial attachment to iron-impregnated granular activated carbon (Fe-GAC) was investigated in this study using Enterococcus faecalis ATCC 10100 and charcoal-based GAC. Two sets of column experiments were performed under different ionic strengths and pH conditions. Breakthrough curves of bacteria were obtained by monitoring effluent. Mass recoveries and attachment rate coefficients were quantified from these curves. In addition, characteristics of Fe-GAC were analyzed using field emission scanning electron microscopy (FESEM) and X-ray spectrometry (EDS). Results show that Fe-GAC was characterized by mosaic-like deposition layers of iron oxides with about 2 μm in thickness. Color mapping with FESEM visualized the spatial distribution of carbon (yellow-green) and iron (red) on Fe-GAC. EDS indicates that iron was distinctly found from Fe-GAC at three peak positions. Results also reveal that bacterial attachment to Fe-GAC was affected by ionic strength and pH.Bacterial mass recoveries decreased from 62.9 to 41.7% with increasing ionic strength from 1 to 50 mM. This indicates that bacterial attachment to the surfaces of Fe-GAC was enhanced with increasing ionic strength. With increasing pH from 6.46 to 9.19, mass recoveries increased from 50.5 to 84.2%, indicating that bacterial attachment to Fe-GAC was reduced with increasing pH. This study demonstrates that iron oxides offer favorable attachment sites for bacteria on the surfaces of Fe-GAC and further improves the knowledge of bacterial removal in Fe-GAC.     

Efficient Solar-Driven Water Harvesting from Arid Air with Metal–Organic Frameworks Modified by Hygroscopic Salt

Freshwater scarcity is a global challenge threatening human survival, especially for people living in arid regions. Sorption-based atmospheric water harvesting (AWH) is an appealing way to solve this problem. However, the state-of-the-art AWH technologies have poor water harvesting performance in arid climates owing to the low water sorption capacity of common sorbents under low humidity conditions. We report a high-performance composite sorbent for efficient water harvesting from arid air by confining hygroscopic salt in a metal–organic framework matrix (LiCl@MIL-101(Cr)). The composite sorbent shows 0.77 g g⁻¹ water sorption capacity at 1.2 kPa vapor pressure (30 % relative humidity at 30 °C) by integrating the multi-step sorption processes of salt chemisorption, deliquescence, and solution absorption. A highly efficient AWH prototype is demonstrated with LiCl@MIL-101(Cr) that can enable the harvesting of 0.45–0.7 kg water per kilogram of material under laboratory and outdoor ambient conditions powered by natural sunlight without optical concentration and additional energy input.     

Near-infrared Aza-BODIPY Dyes Through Molecular Surgery for Enhanced Photothermal and Photodynamic Antibacterial Therapy

The widespread use of high-dose antibiotics will not only lead to the rapid acquisition of antibiotic resistance and increased incidence of drug-resistant bacterial infections, but also produce toxic side effects on normal tissues. Herein, two near-infrared dyes BDP-4PTZ and BDP-4DPA were synthesized, and the electron donors of diphenylamine and phenothiazine with the only difference of sulphur(S)-lock between the two phenyl rings were introduced onto the electron acceptor aza-dipyrromethene boron difluoride(aza-BODIPY) through molecular surgery. Through co-precipitation into nanoparticles(NPs), BDP-4PTZ NPs and BDP-4DPA NPs were fabricated with good biocompatibility. Upon 660 nm photoirradiation, BDP-4PTZ NPs and BDP-4DPA NPs showed excellent photothermal conversion efficiency(43% and 50%, respectively) and reactive oxygen species(ROS) production performance(ca. 3.6 and 6 times higher than that of indocyanine green, respectively). In vitro antibacterial experiments indicated that both NPs could effectively destroy the bacteria's membrane to eradicate drug-resistant bacteria. Furthermore, the bacterial abscess was effectively eliminated after treatment with BDP-4DPA NPs under 660 nm photoirradiation without adverse effects. Thus, through molecular surgery, BDP-4DPA without the S-lock demonstrates synergistic photothermal and photodynamic antimicrobial activities, which is promising for further molecular design towards effective neo-antimicrobial phototherapy.     

Insulator-based dielectrophoresis for the selective concentration and separation of live bacteria in water

Insulator-based dielectrophoresis (iDEP) was utilized to separate and concentrate selectively mixtures of two species of live bacteria simultaneously. Four species of bacteria were studied: the Gram-negative Escherichia coli and the Gram-positive Bacillus subtilis, B. cereus, and B. megaterium. Under an applied direct current (DC) electric field all the bacterial species exhibited negative dielectrophoretic behavior. The dielectrophoretic separations were carried out in a glass microchannel containing an array of insulating posts. The insulating posts in the microchannel produced nonuniformities in the electric field applied along the channel. Mixtures of two species of bacteria were introduced into the microchannel and the electric field was applied. The bacterial species exhibited different dielectrophoretic mobilities under the influence of the nonuniform field. From these experiments a trapping order was established with E. coli trapping at the weakest applied electric field, while the Bacillus species were trapped at different characteristic threshold fields. At stronger applied electric fields, the two different species of bacteria in the microchannel were dielectrophoretically trapped into two spatially distinct bands. The results showed that iDEP has the potential to selectively concentrate and separate different species of bacteria.     

Effect of acid-treated multi-walled carbon nanotubes on thermo-oxidative stability and degradation behavior of silicone rubber

The effect of acid-treated multi-walled carbon nanotubes (MWCNTs) on thermo-oxidative stability and degradation behavior of silicone rubber (SR) was evaluated. Raman microscopy, Fourier transformed infrared spectroscopy, X-ray photoelectron spectroscopy and thermogravimetric (TG) analysis were performed to characterize the surface states of MWCNTs samples. The results demonstrated that after acid treatment the nanodefects and surface oxygen-containing groups (mainly hydroxyl and carboxyl groups) were formed and the number of them was gradually increased by increasing the treatment time. Then these MWCNTs were embedded into SR matrix. Furthermore, the thermo-oxidative stability and degradation behavior of MWCNTs/SR composites were studied using thermogravimetric/infrared spectrometry (TG-IR). Thermo-oxidative stability test in air revealed that the degradation of SR, at relatively low temperature, was mainly due to the oxidation of Si-CH₃ side groups and the generation of free radicals. This behavior was hindered by the MWCNTs’ surface nanodefects and hydroxyl groups, as proved by TG-IR study which revealed that the amount of carbonyl compounds was reduced more than 60%, compared with that of neat SR. Therefore, acid treatment led a better thermo-oxidative stability of MWCNTs/SR. For 4hAT-MWCNTs/SR, with maximum hydroxyl groups on MWCNTs surface, the T_i (defined as the temperature for 5% mass loss) of it is increased by 34.8 °C compared to that of neat SR, and even increased by 18.5 °C compared with that of raw-MWCNTs/SR.     

Efficient Solar‐Driven Water Harvesting from Arid Air with Metal–Organic Frameworks Modified by Hygroscopic Salt

Freshwater scarcity is a global challenge threatening human survival, especially for people living in arid regions. Sorption‐based atmospheric water harvesting (AWH) is an appealing way to solve this problem. However, the state‐of‐the‐art AWH technologies have poor water harvesting performance in arid climates owing to the low water sorption capacity of common sorbents under low humidity conditions. We report a high‐performance composite sorbent for efficient water harvesting from arid air by confining hygroscopic salt in a metal–organic framework matrix (LiCl@MIL‐101(Cr)). The composite sorbent shows 0.77 g g^?1 water sorption capacity at 1.2 kPa vapor pressure (30 % relative humidity at 30 °C) by integrating the multi‐step sorption processes of salt chemisorption, deliquescence, and solution absorption. A highly efficient AWH prototype is demonstrated with LiCl@MIL‐101(Cr) that can enable the harvesting of 0.45–0.7 kg water per kilogram of material under laboratory and outdoor ambient conditions powered by natural sunlight without optical concentration and additional energy input.     

A Synergistic Capture Strategy for Enhanced Detection and Elimination of Bacteria

Despite the advanced detection and sterilization techniques available today, the sensitive diagnosis and complete elimination of bacterial infections remain a significant challenge. A strategy is reported for efficient bacterial capture (ca. 90 %) based on the synergistic effect of the nanotopography and surface chemistry of the substrate on bacterial attachment and adhesion. The outstanding bacterial‐capture capability of the functionalized nanostructured substrate enables rapid and highly sensitive bacterial detection down to trace concentrations of pathogenic bacteria (10 colony‐forming units mL^?1). In addition, this synergistic biocapture substrate can be used for efficient bacterial elimination and shows great potential for clinical antibacterial applications.     

Seasonal dynamics of dimethylarsinic‐acid‐decomposing bacteria dominating in Lake Kahokugata

Decomposition processes of organoarsenic compounds significantly influence arsenic cycles in aquatic environments, and such processes depend on bacterial activity. However, the bacterial characteristics in these environments are obscure. Accordingly, we observed seasonal variations of arsenic species and the bacterial population decomposing dimethylarsinic acid (DMAA) in Lake Kahokugata from April 2002 to January 2003. Monitoring of bacterial biomass involving DMAA decomposition using the most probable number procedure showed that the bacterial cell densities ranged from 36 to 3600 ml^?1. On the other hand, methylated arsenic was not detected during the experimental period, although the inorganic arsenic concentration was over 4 nM . This suggests that bacteria remineralized methylated arsenic species to inorganic arsenic. Furthermore, the composition of bacterial communities involving DMAA decomposition was examined by restriction‐fragment‐length polymorphism analysis of the 16S rDNA nucleotide. As a result, a total of 49 isolates were classified into 10 type groups, and 32 of these isolates belonged to three dominant type groups. Phylogenetic analysis using 16S rDNA partial sequences (ca 320 bp) suggests that the representative isolates of the dominant type groups are specific to the summer or winter season. Moreover, as a result of the culture experiments to examine DMAA decomposition activity, the representative isolates decomposed 1 µM DMAA at a decomposition percentage of below 80%. In conclusion, some bacterial communities in a specific season can decompose DMAA to varying degrees, contributing to the annual cycle of arsenic species. Copyright © 2005 John Wiley & Sons, Ltd.