Comparative analysis of biofilm formation by Bacillus cereus reference strains and undomesticated food isolates and the effect of free iron
Hayrapetyan, H. ; Muller, L.K. ; Tempelaars, M.H. ; Abee, T. ; Nierop Groot, M.N. - \ 2015
International Journal of Food Microbiology 200 (2015). - ISSN 0168-1605 - p. 72 - 79.
pseudomonas-aeruginosa - stainless-steel - processing environments - twitching motility - adhesion - surface - attachment - contamination - typhimurium - sporulation
Biofilm formation of Bacillus cereus reference strains ATCC 14579 and ATCC 10987 and 21 undomesticated food isolates was studied on polystyrene and stainless steel as contact surfaces. For all strains, the biofilm forming capacity was significantly enhanced when in contact with stainless steel (SS) as a surface as compared to polystyrene (PS). For a selection of strains, the total CFU and spore counts in biofilms were determined and showed a good correlation between CFU counts and total biomass of these biofilms. Sporulation was favoured in the biofilm over the planktonic state. To substantiate whether iron availability could affect B. cereus biofilm formation, the free iron availability was varied in BHI by either the addition of FeCl3 or by depletion of iron with the scavenger 2,2-Bipyridine. Addition of iron resulted in increased air-liquid interface biofilm on polystyrene but not on SS for strain ATCC 10987, while the presence of Bipyridine reduced biofilm formation for both materials. Biofilm formation was restored when excess FeCl3 was added in combination with the scavenger. Further validation of the iron effect for all 23 strains in microtiter plate showed that fourteen strains (including ATCC10987) formed a biofilm on PS. For eight of these strains biofilm formation was enhanced in the presence of added iron and for eleven strains it was reduced when free iron was scavenged. Our results show that stainless steel as a contact material provides more favourable conditions for B. cereus biofilm formation and maturation compared to polystyrene. This effect could possibly be linked to iron availability as we show that free iron availability affects B. cereus biofilm formation.
Listeria monocytogenes repellence by enzymatically modified PES surfaces
Veen, S. van der; Nady, N. ; Franssen, M.C.R. ; Zuilhof, H. ; Boom, R.M. ; Abee, T. ; Schroën, C.G.P.H. - \ 2015
Journal of Applied Polymer Science 132 (2015)10. - ISSN 0021-8995 - 6 p.
stainless-steel - catalyzed modification - biofilm formation - attachment - growth - membranes - water - acid - functionalization - hydrophobicity
: The effect of enzyme-catalyzed modification of poly(ethersulfone) (PES) on the adhesion and biofilm formation of two Listeria monocytogenes strains is evaluated under static and dynamic flow conditions. PES has been modified with gallic acid, ferulic acid and 4-hydroxybenzoic acid. The surfaces modified with any of these compounds show up to 70% reduced adhesion of L. mono-cytogenes under static conditions and up to 95% under dynamic flow conditions compared with unmodified surfaces. Also, under static conditions the formation of biofilms is reduced by 70%. These results indicate that the brush structures that are formed by the polymers on the PES surface directly influence the ability of microorganisms to interact with the surface, thereby reducing attachment and biofilm formation of L. monocytogenes. Based on these results, it is expected that enzyme-catalyzed surface modification is a promising tool to reduce microbial adhesion and biofilm formation
Hydrolytic and Thermal Stability of Organic Monolayers on Various Inorganic Substrates
Bhairamadgi, N.S. ; Pujari, S.P. ; Trovela, F.G. ; Debrassi, A. ; Khamis, A.A.M. ; Alonso Carnicero, J.M. ; Zahrani, A.A. Al; Wennekes, T. ; Al-Turaif, H.A. ; Rijn, C.J.M. van; Alhamed, Y.A. ; Zuilhof, H. - \ 2014
Langmuir 30 (2014)20. - ISSN 0743-7463 - p. 5829 - 5839.
self-assembled monolayers - hydrogen-terminated silicon - oxidized si(100) surface - alkyl monolayers - nitride surfaces - aluminum-oxide - gold - phosphonate - films - attachment
A comparative study is presented of the hydrolytic and thermal stability of 24 different kinds of monolayers on Si(111), Si(100), SiC, SiN, SiO2, CrN, ITO, PAO, Au, and stainless steel surfaces. These surfaces were modified utilizing appropriate organic compounds having a constant alkyl chain length (C18), but with different surface-reactive groups, such as 1-octadecene, 1-octadecyne, 1-octadecyltrichlorosilane, 1-octadecanethiol, 1-octadecylamine and 1-octadecylphosphonic acid. The hydrolytic stability of obtained monolayers was systematically investigated in triplicate in constantly flowing aqueous media at room temperature in acidic (pH 3), basic (pH 11), phosphate buffer saline (PBS) and deionized water (neutral conditions), for a period of 1 day, 7 days, and 30 days, yielding 1152 data points for the hydrolytic stability. The hydrolytic stability was monitored by static contact angle measurements and X-ray photoelectron spectroscopy (XPS). The covalently bound alkyne monolayers on Si(111), Si(100), and SiC were shown to be among the most stable monolayers under acidic and neutral conditions. Additionally, the thermal stability of 14 different monolayers was studied in vacuum using XPS at elevated temperatures (25–600 °C). Similar to the hydrolytic stability, the covalently bound both alkyne and alkene monolayers on Si(111), Si(100) and SiC started to degrade from temperatures above 260 °C, whereas on oxide surfaces (e.g., PAO) phosphonate monolayers even displayed thermal stability up to ~500 °C.
Influence of Fertilizer Microdosing on Strigolactone Production and Striga hermonthica Parasitism in Pearl Millet
Jamil, M. ; Charnikhova, T. ; Jamil, T. ; Ali, Z. ; Mohemed Ahmed Mohamed, N.E. ; Mourik, T. van; Bouwmeester, H.J. - \ 2014
International Journal of Agriculture & Biology 16 (2014). - ISSN 1560-8530 - p. 935 - 940.
sorghum-bicolor - infestation - resistance - attachment - cultivars - africa
Parasitism by the root-parasitic plant, Striga (Striga hermonthica L.), is a main threat to pearl millet production in sub-Saharan Africa and nutrient deficiency aggravates this problem, often leading to complete failure of pearl millet crops. Like many other species, pearl millet secretes germination stimulants (strigolactones) into the soil in response to mineral nutrient deficiency, which triggers Striga seed germination resulting in infection. A greenhouse experiment was conducted to evaluate the influence of different doses of di-ammonium phosphate (DAP) fertilizer on strigolactone production and Striga infection in three different African pearl millet cultivars (KBH, Sadore Local and Striga resistance). All the pearl millet genotypes produced varying amounts of different strigolactones like orobanchol, epi-orobanchol, orobanchyl acetate and 5-deoxystrigol, the level of which decreases with increasing doses of DAP. The control treatment (no DAP) showed maximum Striga germination, emergence and dry biomass production in all cultivars of pearl millet. Supply of DAP fertilizer up to 4 g per hill suppressed Striga germination by 69, 64 and 59%; emergence by 87, 85 and 95% and dry biomass by 91, 98 and 83% in cvs KBH, Sadore Local and Striga Resistance, respectively. The present findings reveal that DAP fertilizer minimizes strigolactones production and, as a result, reduces Striga infection in pearl millet. Low doses of DAP fertilizer is a promising strategy to lower the destructive effect of Striga on pearl millet. The use of small doses of DAP fertilizer combined with resistant crop cultivars, intercropping with legumes and hand pulling of Striga at flowering in an integrated Striga control strategy should be developed to help African farmers control this noxious weed.
Hexadecadienyl Monolayers on Hydrogen-Terminated Si(III): Faster Monolayer Formation and Improved Surface Coverage Using the Enyne Moiety
Rijksen, B.M.G. ; Pujari, S.P. ; Scheres, L.M.W. ; Rijn, C.J.M. van; Baio, J.E. ; Weidner, T. ; Zuilhof, H. - \ 2012
Langmuir 28 (2012)16. - ISSN 0743-7463 - p. 6577 - 6588.
self-assembled monolayers - silicon surfaces - alkyl monolayers - organic monolayers - x-ray - molecular simulation - visible-light - si - spectroscopy - attachment
To further improve the coverage of organic monolayers on hydrogen-terminated silicon (H–Si) surfaces with respect to the hitherto best agents (1-alkynes), it was hypothesized that enynes (H–C=C–HC-CH–R) would be even better reagents for dense monolayer formation. To investigate whether the increased delocalization of ß-carbon radicals by the enyne functionality indeed lowers the activation barrier, the kinetics of monolayer formation by hexadec-3-en-1-yne and 1-hexadecyne on H–Si(111) were followed by studying partially incomplete monolayers. Ellipsometry and static contact angle measurements indeed showed a faster increase of layer thickness and hydrophobicity for the hexadec-3-en-1-yne-derived monolayers. This more rapid monolayer formation was supported by IRRAS and XPS measurements that for the enyne show a faster increase of the CH2 stretching bands and the amount of carbon at the surface (C/Si ratio), respectively. Monolayer formation at room temperature yielded plateau values for hexadec-3-en-1-yne and 1-hexadecyne after 8 and 16 h, respectively. Additional experiments were performed for 16 h at 80° to ensure full completion of the layers, which allows comparison of the quality of both layers. Ellipsometry thicknesses (2.0 nm) and contact angles (111–112°) indicated a high quality of both layers. XPS, in combination with DFT calculations, revealed terminal attachment of hexadec-3-en-1-yne to the H–Si surface, leading to dienyl monolayers. Moreover, analysis of the Si2p region showed no surface oxidation. Quantitative XPS measurements, obtained via rotating Si samples, showed a higher surface coverage for C16 dienyl layers than for C16 alkenyl layers (63% vs 59%). The dense packing of the layers was confirmed by IRRAS and NEXAFS results. Molecular mechanics simulations were undertaken to understand the differences in reactivity and surface coverage. Alkenyl layers show more favorable packing energies for surface coverages up to 50–55%. At higher coverages, this packing energy rises quickly, and there the dienyl packing becomes more favorable. When the binding energies are included the difference becomes more pronounced, and dense packing of dienyl layers becomes more favorable by 2–3 kcal/mol. These combined data show that enynes provide the highest-quality organic monolayers reported on H–Si up to now.
Photochemical Grafting and Patterning of Organic Monolayers on Indium Tin Oxide Substrates
Li, Y. ; Zuilhof, H. - \ 2012
Langmuir 28 (2012)12. - ISSN 0743-7463 - p. 5350 - 5359.
self-assembled monolayers - click chemistry - terminated monolayers - surface modification - biomolecular interfaces - aqueous-solutions - molecular layers - silicon - functionalization - attachment
Covalently attached organic layers on indium tin oxide (ITO) surfaces were prepared by the photochemical grafting with 1-alkenes. The surface modification was monitored with static water contact angle, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) measurements. Hydrophobic methyl-terminated ITO surfaces can be obtained via the grafting of tetradec-1-ene, whereas the attachment of ¿-functionalized 1-alkenes leads to functionalized ITO surfaces. The use of a C=C—Ge(CH3)3 terminus allows for facile tagging of the surface with an azido group via a one-pot deprotection/click reaction, resulting in bio/electronically active interfaces. The combination of nonaggressive chemicals (alkenes), mild reaction conditions (room temperature), and a light-induced grafting that facilitates the direct patterning of organic layers makes this simple approach highly promising for the development of ITO-based (bio)electronic devices.
Bioinspired pressure actuated adhesive system
Paretkar, D.R. ; Kamperman, M.M.G. ; Schneider, A.S. ; Martina, D. ; Creton, C. ; Arzt, E. - \ 2011
Materials science & engineering. C, Biomimetic materials, sensors and systems 31 (2011)6. - ISSN 0928-4931 - p. 1152 - 1159.
biomimetic fibrillar interfaces - gecko foot-hair - contact mechanics - surfaces - attachment - friction - shape - devices - design - layer
We developed a dry synthetic adhesive system inspired by gecko feet adhesion that can switch reversibly from adhesion to non-adhesion with applied pressure as external stimulus. Micropatterned polydimethylsiloxane (PDMS) surfaces with pillars of 30 µm length and 10 µm diameter were fabricated using photolithography and moulding. Adhesion properties were determined with a flat probe as a function of preload. For low and moderate applied compressive preloads, measured adhesion was 7.5 times greater than on flat controls whereas for high applied preloads adhesion dropped to very low values. In situ imaging shows that the increased preload caused the pillars to deform by bending and/or buckling and to lose their adhesive contact. The elasticity of PDMS aids the pillar recovery to the upright position upon removal of preload enabling repeatability of the switch.
Generation of Variants in Listeria monocytogenes Continuous-Flow Biofilms Is Dependent on Radical-Induced DNA Damage and RecA-Mediated Repair
Veen, S. van der; Abee, T. - \ 2011
PLoS ONE 6 (2011)12. - ISSN 1932-6203
sos response - disinfectant resistance - induced mutagenesis - egd-e - oxygen - pathogenesis - environment - communities - superoxide - attachment
The food-borne pathogen Listeria monocytogenes is a Gram-positive microaerophilic facultative anaerobic rod and the causative agent of the devastating disease listeriosis. L. monocytogenes is able to form biofilms in the food processing environment. Since biofilms are generally hard to eradicate, they can function as a source for food contamination. In several occasions biofilms have been identified as a source for genetic variability, which potentially can result in adaptation of strains to food processing or clinical conditions. However, nothing is known about mutagenesis in L. monocytogenes biofilms and the possible mechanisms involved. In this study, we showed that the generation of genetic variants was specifically induced in continuous-flow biofilms of L. monocytogenes, but not in static biofilms. Using specific dyes and radical inhibitors, we showed that the formation of superoxide and hydroxyl radicals was induced in continuous-flow biofilms, which was accompanied with in an increase in DNA damage. Promoter reporter studies showed that recA, which is an important component in DNA repair and the activator of the SOS response, is activated in continuous-flow biofilms and that activation was dependent on radical-induced DNA damage. Furthermore, continuous-flow biofilm experiments using an in-frame recA deletion mutant verified that RecA is required for induced generation of genetic variants. Therefore, we can conclude that generation of genetic variants in L. monocytogenes continuous-flow biofilms results from radical-induced DNA damage and RecA-mediated mutagenic repair of the damaged DNA
Perspectives on landscape identity, a conceptual challenge
Stobbelaar, D.J. ; Pedroli, B. - \ 2011
Landscape Research 36 (2011)3. - ISSN 0142-6397 - p. 321 - 339.
place-identity - regional identity - european landscape - community - sense - representation - attachment - construction - perception - diversity
The concept of landscape identity is often referred to in landscape policy and planning. A clear definition of the concept is lacking however. This is problematic because the term ‘landscape identity’ can have many different meanings and thus easily lead to confusion. We define landscape identity as ‘the perceived uniqueness of a place’ and endeavour to describe the content of this definition more concisely. Within this context the paper introduces the framework of the Landscape Identity Circle for the various dimensions of landscape identity based on two axes: differentiation between spatial as opposed to existential identity, and differentiation between personal and cultural landscape identity. This framework is valuable in positioning research approaches and disciplines addressing landscape identity
Molecular Modeling of Alkyl and Alkenyl Mono layers on Hydrogen-Terminated Si(111)
Scheres, L.M.W. ; Rijksen, B.M.G. ; Giesbers, M. ; Zuilhof, H. - \ 2011
Langmuir 27 (2011)3. - ISSN 0743-7463 - p. 972 - 980.
organic monolayers - silicon surfaces - formation mechanisms - si - simulation - chemistry - quality - electronics - attachment - reactivity
On H-Si(111) surfaces monolayer formation with 1-alkenes results in alkyl monolayers with a Si-C-C linkage, while 1-alkynes yield alkenyl monolayers with a Si-C-C linkage. Recently, considerable structural differences between both types of monolayers were observed, including an increased thickness, improved packing, and higher surface coverage for the alkenyl monolayers. The precise origin thereof could experimentally not be clarified yet. Therefore, octadecyl and octadecenyl monolayers on Si(111) were studied in detail by molecular modeling via PCFF molecular mechanics calculations on periodically repeated slabs of modified surfaces. After energy minimization the packing energies, structural properties, close contacts, and deformations of the Si surfaces of monolayers structures with various substitution percentages and substitution patterns were analyzed. For the octadecyl monolayers all data pointed to a substitution percentage close to 50-55%, which is due the size of the CH2 groups near the Si surface. This agrees with literature and the experimentally determined coverage of octadecyl monolayers. For the octadecenyl monolayers the minimum in packing energy per chain is calculated around 60% coverage, i.e., close to the experimentally observed value of 65% [Scheres et al. Langmuir 2010, 26, 4790], and this packing energy is less dependent on the substitution percentage than calculated for alkyl layers. Analysis of the chain conformations, close contacts, and Si surface deformation clarifies this, since even at coverages above 60% a relatively low number of close contacts and a negligible deformation of the Si was observed. In order to evaluate the thermodynamic feasibility of the monolayer structures, we estimated the binding energies of 1-alkenes and 1-alkynes to the hydrogen-terminated Si surface at a range of surface coverages by composite high-quality G3 calculations and determined the total energy of monolayer formation by adding the packing energies and the binding energies. It was shown that due to the significantly larger reaction exothermicity of the 1-alkynes, thermodynamically even a substitution percentage as high as 75% is possible for octadecenyl chains. However, because sterically (based on the van der Waals footprint) a coverage of 69% is the maximum for alkyl and alkenyl monolayers, the optimal substitution percentage of octadecenyl monolayers will be presumably close to this latter value, and the experimentally observed 65% is likely close to what is experimentally maximally obtainable with alkenyl monolayers
Mimicking the silicon surface: reactivity of silyl radical cations toward nucleophiles
Rijksen, B.M.G. ; Lagen, B. van; Zuilhof, H. - \ 2011
Journal of the American Chemical Society 133 (2011)13. - ISSN 0002-7863 - p. 4998 - 5008.
hydrogen-terminated silicon - organic monolayers - alkyl monolayers - si(111) surfaces - porous silicon - si - functionalization - oligosilanes - attachment - 1-alkenes
Radical cations of selected low molecular-weight silicon model compounds were obtained by photoinduced electron transfer. These radical cations react readily with a variety of nucleophiles, regularly used in monolayer fabrication onto hydrogen-terminated silicon. From time-resolved kinetics, it was concluded that the reactions proceed via a bimolecular nucleophilic attack to the radical cation. A secondary kinetic isotope effect indicated that the central Si-H bond is not cleaved in the rate-determining step. Apart from substitution products, also hydrosilylation products were identified in the product mixtures. Observation of the substitution products, combined with the kinetic data, point to an bimolecular reaction mechanism involving Si-Si bond cleavage. The products of this nucleophilic substitution can initiate radical chain reactions leading to hydrosilylation products, which can independently also be initiated by dissociation of the radical cations. Application of these data to the attachment of organic monolayers onto hydrogen-terminated Si surfaces via hydrosilylation leads to the conclusion that the delocalized Si radical cation (a surface-localized hole) can initiate the hydrosilylation chain reaction at the Si surface. Comparison to monolayer experiments shows that this reaction only plays a significant role in the initiation, and not in the propagation steps of Si-C bond making monolayer formation
Understanding stakeholders' attitudes toward water management interventions: Role of place meanings
Jacobs, M.H. ; Buijs, A.E. - \ 2011
Water Resources Research 47 (2011)1. - ISSN 0043-1397 - 11 p.
resources management - value orientations - river management - sense - behavior - restoration - netherlands - perceptions - dimensions - attachment
Water resource managers increasingly need to take the opinions of stakeholders into account when planning interventions. We studied stakeholders' concerns in two water management planning contexts, focusing on the meanings assigned to places and on attitudes toward proposed interventions. Semistructured interviews were held, and public meetings were observed in order to collect data. Five categories of place meanings emerged from the analysis: beauty (esthetic judgments), functionality (ways of use), attachment (feelings of belonging), biodiversity (meanings pertaining to nature), and risk (worries about current or future events). These categories reflect the basic dimensions of sense of place. Our results suggest that stakeholders' attitudes toward proposed interventions are, to a great extent, derived from their place meanings. Discussing place meanings during participatory planning processes could contribute substantially to successful water management.
Photothermal Micro- and Nanopatterning of Organic/Silicon Interfaces
Klingebiel, B. ; Scheres, L.M.W. ; Franzka, S. ; Zuilhof, H. ; Hartmann, N. - \ 2010
Langmuir 26 (2010)9. - ISSN 0743-7463 - p. 6826 - 6831.
self-assembled monolayers - hydrogen-terminated silicon - atomic-force microscope - scanned probe oxidation - organic monolayers - alkylsiloxane monolayers - alkyl monolayers - visible-light - surfaces - attachment
Photothermal laser processing of organic monolayers on oxide-free silicon substrates under ambient conditions is investigated. Organic monolayers on Si(100) and Si(111) substrates are prepared via hydrosilylation of H-terminated silicon samples in neat 1-hexadecene and 1-hexadecyne, respectively. Laser processing at ¿ = 514 nm and a 1/e2 spot diameter of 2.6 µm results in local decomposition of the monolayers and oxidation of the exposed substrate. In agreement with the high thermal and chemical stability of these monolayers, a thermokinetic analysis of the data from experiments at distinct laser powers and pulse lengths points to a highly activated process. As a result, processing is strongly nonlinear and allows for subwavelength patterning, with line widths between 0.4 and 1.4 µm. Most remarkably, upon fabrication of dense line patterns, narrow organic monolayer stripes with sharp edges and lateral dimensions of 80 nm are formed. This opens up new perspectives in photothermal engineering of organic/silicon interfaces, e.g., for hybrid microelectronic and sensor applications
Functional monolayers on oxide-free silicon surfaces via thiol-ene click chemistry
Caipa Campos, M.A. ; Paulusse, J.M.J. ; Zuilhof, H. - \ 2010
Chemical Communications 46 (2010)30. - ISSN 1359-7345 - p. 5512 - 5514.
hydrogen-terminated silicon - self-assembled monolayers - organic monolayers - visible-light - attachment - peptide
Thiol–ene click chemistry was used for the attachment of a variety of functional molecules onto oxide-free Si(111) surfaces using very mild conditions; the efficient nature of this coupling strategy allowed for successful light-induced micropatterning and thus provides a novel route towards biofunctional electronics
Light-enhanced microcontact printing of 1-alkynes onto hydrogen-terminated silicon
Maat, J. ter; Yang, M. ; Scheres, L.M.W. ; Kuypers, S. ; Zuilhof, H. - \ 2010
Chemical Communications 46 (2010)42. - ISSN 1359-7345 - p. 8005 - 8007.
self-assembled monolayers - scanning-electron-microscopy - organic monolayers - alkyl monolayers - visible-light - surfaces - 1-alkenes - alkanethiols - attachment - chemistry
method for the direct patterning of 1-alkynes onto hydrogen-terminated silicon is presented. It combines microcontact printing with illumination through the stamp, and results in the formation of an alkenyl monolayer. The formation of heterogeneous monolayers is demonstrated by subsequent backfilling
Importance of SigB for Listeria monocytogenes static and continuous flow biofilm formation and disinfectant resistance
Veen, S. van der; Abee, T. - \ 2010
Applied and Environmental Microbiology 76 (2010)23. - ISSN 0099-2240 - p. 7854 - 7860.
benzalkonium-chloride resistance - food-processing environment - factor sigma(b) - sos response - stress resistance - hydrogen-peroxide - egd-e - attachment - acid - survival
Listeria monocytogenes is a food-borne pathogen that is able to form biofilms in food processing facilities. Biofilms are generally more resistant to antimicrobial agents, making it difficult to eradicate them during cleanup procedures. So far, little is known about the function of stress resistance mechanisms in biofilm formation and their resistance to disinfectants. In this study, we investigated the role of sigB, which encodes a major transcriptional regulator of stress response genes, in L. monocytogenes static and continuous-flow biofilm formation and its function in the resistance of biofilm cells to the disinfectants benzalkonium chloride and peracetic acid. Quantitative real-time PCR and promoter reporter studies showed that sigB is activated in static and continuous-flow biofilms. Biofilm formation studies using an in-frame sigB deletion mutant and complementation mutant showed that the presence of SigB is required to obtain wild-type levels of both static and continuous-flow biofilms. Finally, disinfection treatments of planktonically grown cells and cells dispersed from static and continuous-flow biofilms showed that SigB is involved in the resistance of both planktonic cells and biofilms to the disinfectants benzalkonium chloride and peracetic acid.
Dependence of continuous-flow biofilm formation by Listeria monocytogenes EGD-e on SOS response factor YneA
Veen, S. van der; Abee, T. - \ 2010
Applied and Environmental Microbiology 76 (2010)6. - ISSN 0099-2240 - p. 1992 - 1995.
dna-polymerase - cell-division - attachment - mutagenesis - protein
Listeria monocytogenes was previously shown to form biofilms composed of a network of knitted chains under continuous-flow conditions. Here we show that the SOS response is activated under these conditions and that deletion of its regulon member yneA results in diminished biofilm formation under continuous-flow conditions
Tuning the Electronic Communication between Redox Centers Bound to Insulating Surfaces
Zigah, D. ; Herrier, C. ; Scheres, L.M.W. ; Giesbers, M. ; Fabre, B. ; Hapiot, P. ; Zuilhof, H. - \ 2010
Angewandte Chemie-International Edition 49 (2010)18. - ISSN 1433-7851 - p. 3157 - 3160.
scanning electrochemical microscopy - organic monolayers - ferrocene derivatives - active dendrimers - si(111) surfaces - visible-light - logic gates - silicon - attachment - alkyl
Controlling communication: The electronic communication between ferrocenyl centers bound to insulating silicon surfaces can be efficiently controlled; scanning electrochemical microscopy (SECM) shows that both the surface coverage of the electroactive units and the nature of the redox mediator allow for this control. The lateral charge propagation can be precisely tuned from an extremely slow to a very fast process
Social interactions in urban parks: Stimulating social cohesion?
Peters, K.B.M. ; Elands, B.H.M. ; Buijs, A.E. - \ 2010
Urban Forestry and Urban Greening 9 (2010)2. - ISSN 1618-8667 - p. 93 - 100.
neighborhoods - management - attachment - values
People from all ethnic backgrounds spend some of their leisure time in green areas. This study found that urban parks are more inclusive green places than non-urban green areas, and that urban parks can promote social cohesion. The objective of the research was to establish the extent to which urban parks facilitate social cohesion and how social interaction and place attachment can contribute to such cohesion. Quantitative research (a survey) and qualitative research (observations and interviews) carried out in five urban parks in the Netherlands revealed that there are many similarities in the ways that ethnic groups use urban parks and in the meanings of such parks to these groups. Urban parks are sites where different ethnic groups mingle and where informal and cursory interactions can stimulate social cohesion. Furthermore, being involved and concerned with parks can facilitate attachment to these places. Urban parks can provide a vital locality where everyday experiences are shared and negotiated with a variety of people. The design of a park, its location and people's image of the park in combination with the cultural characteristics of various ethnic groups inform the opportunities for intercultural interactions
Public support for river restoration. A mixed-method study into local residents' support for and framing of river management and ecological restoration in the Dutch floodplains
Buijs, A.E. - \ 2009
Journal of Environmental Management 90 (2009)8. - ISSN 0301-4797 - p. 2680 - 2689.
water management - landscape - representations - attachment
In many European countries, accommodating water has become the dominant paradigm in river management. In the Netherlands, extensive river restoration projects are being implemented, many of which draw serious opposition from the public. To investigate the causes of such opposition, a comprehensive study of public attitudes towards river restoration was conducted in three floodplains, both before and after river restoration. The study combined quantitative questionnaires (N = 562) with open interviews (N = 29). This paper describes how local residents perceive the effects of river restoration on landscape quality and how residents and protest groups use landscape quality in combination with other arguments to strategically frame river management policies. Results show that measurement of the perceived outcomes of nature restoration needs to be complemented by a more dynamic type of research, focusing on the social processes of the framing of restoration plans. Theoretically, the paper aims to contribute to the development of a rigorous research strategy to study framing processes in environmental management, using a mixed-methods approach. In general, local residents are supportive of river restoration projects. Although restoration may diminish feelings of attachment to an area, for most people this negative effect is compensated by the positive effects on scenic beauty and perceived protection from flooding. However, these positive effects may become contested because of the active framing of river restoration by protest groups. Residents use three distinct frames to give meaning to river restoration projects: (i) an attachment frame, focusing on cultural heritage and place attachment (ii) an attractive nature frame, focusing on nature as attractive living space and the intrinsic value of nature (iii) a rurality frame, focusing on rural values, agriculture and cultural heritage. Resistance to river restoration plans stems from the attachment and rurality frames. People using these frames challenge safety arguments for river restoration and highlight potential threats to sense of place and to agriculture. In the areas surveyed, the project initiator's focus on biodiversity and safety did not resonate very well among the local community, because of their diverging views on nature. Practical implications of the study include the need to incorporate public perception into river restoration projects and the potential for project initiators to form strategic alliances with local residents to promote ecological restoration in combination with river restoration.