The potential of electron beam radiation for simultaneous surface modification and bioresorption control of PLLA

Bioresorbable polymers have been widely investigated as materials exhibiting significant potential for successful application in the fields of tissue engineering and drug delivery. Further to the ability to control degradation, surface engineering of polymers has been highlighted as a key method central to their development. Previous work has demonstrated the ability of electron beam (e-beam) technology to control the degradation profiles and bioresorption of a number of commercially relevant bioresorbable polymers (poly-l-lactic acid (PLLA), Llactide/DL-lactide co-polymer (PLDL) and poly(lactic-co-glycolic acid (PLGA)). This work investigates the further potential of ebeam technology to impart added biofunctionality through the manipulation of polymer (PLLA) surface properties. PLLA samples were subjected to e-beam treatments in air, with varying beam energies and doses. Surface characterization was then performed using contact angle analysis, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and atomic force microscopy. Results demonstrated a significant increase in surface wettability post e-beam treatment. In correlation with this, XPS data showed the introduction of oxygen-containing functional groups to the surface of PLLA. Raman spectroscopy indicated chain scission in the near surface region of PLLA (as predicted). However, e-beam effects on surface properties were not shown to be dependent on beam energy or dose. E-beam irradiation did not seem to affect the surface roughness of PLLA as a direct consequence of the treatment.

Functional responses of the intertidal amphipod Echinogammarus marinus: effects of prey supply, model selection and habitat complexity.

The influence of predation in structuring ecological communities can be informed by examining the shape and magnitude of the functional response of predators towards prey. We derived functional responses of the ubiquitous intertidal amphipod Echinogammarus marinus towards one of its preferred prey species, the isopod Jaera nordmanni. First, we examined the form of the functional response where prey were replaced following consumption, as compared to the usual experimental design where prey density in each replicate is allowed to deplete. E. marinus exhibited Type II functional responses, i.e. inversely density-dependent predation of J. nordmanni that increased linearly with prey availability at low densities, but decreased with further prey supply. In both prey replacement and non-replacement experiments, handling times and maximum feeding rates were similar. The non-replacement design underestimated attack rates compared to when prey were replaced. We then compared the use of Holling’s disc equation (assuming constant prey density) with the more appropriate Rogers’ random predator equation (accounting for prey depletion) using the prey non-replacement data. Rogers’ equation returned significantly greater attack rates but lower maximum feeding rates, indicating that model choice has significant implications for parameter estimates. We then manipulated habitat complexity and found significantly reduced predation by the amphipod in complex as opposed to simple habitat structure. Further, the functional response changed from a Type II in simple habitats to a sigmoidal, density-dependent Type III response in complex habitats, which may impart stability on the predator−prey interaction. Enhanced habitat complexity returned significantly lower attack rates, higher handling times and lower maximum feeding rates. These findings illustrate the sensitivity of the functional response to variations in prey supply, model selection and habitat complexity and, further, that E. marinus could potentially determine the local exclusion and persistence of prey through habitat-mediated changes in its predatory functional responses.

Has habitat heterogeneity promoted phenotypic and ecological sub-structuring among a Coregonus lavaretus population in a large Scottish lake?

Differences in stable-isotope values, morphology and ecology in whitefish Coregonus lavaretus were investigated between the three basins of Loch Lomond. The results are discussed with reference to a genetic investigation to elucidate any substructuring or spawning site fidelity. Foraging fidelity between basins of Loch Lomond was indicated by delta 13C and delta 15N values of C. lavaretus muscle tissue. There was, however, no evidence of the existence of sympatric morphs in the C. lavaretus population. A previous report of two C. lavaretus 'species' in Loch Lomond probably reflects natural variation between individuals within a single mixed population.

A PLATE ASSAY FOR THE DETECTION OF ORGANOPHOSPHONATE MINERALIZATION BY ENVIRONMENTAL BACTERIA, AND ITS MODIFICATION AS AN ACTIVITY STAIN FOR IDENTIFICATION OF THE CARBON-PHOSPHORUS BOND-CLEAVAGE ENZYME PHOSPHONOACETATE HYDROLASE

A replica plate screening technique, based on the acid molybdate assay for detection of phosphate has been developed to permit the detection of microorganisms capable of mineralizing organophosphonates. The method was further adapted as the basis of an activity stain for the detection of the carbon - phosphorus bond cleavage enzyme phosphonoacetate hydrolase in PAGE gels.

Identifying optimal sites for natural recovery and restoration of impacted biogenic habitats in a special area of conservation using hydrodynamic and habitat suitability modelling

Selection of sites for successful restoration of impacted shellfish populations depends on understanding the dispersion capability and habitat requirements of the species involved. In Strangford Lough, Northern Ireland, the horse mussel (Modiolus modiolus) biogenic reefs cover only a fraction of their historical range with the remaining reefs badly damaged and requiring restoration. Previous experimental trials suggest that translocation of horse mussels accelerates reef recovery and has therefore been proposed as a suitable restoration technique. We used a series of coupled hydrodynamic and particle dispersal models to assess larval dispersion from remnant and translocated populations to identify suitable areas for adult live M. modiolus translocation in Strangford Lough, Northern Ireland. A maximum entropy model (MAXENT) was used to identify if dispersing larvae could reach habitat suitable for adult M. modiolus. From these we predicted if translocated mussels will reseed themselves or be able to act as larval sources for nearby reefs. The dispersal models showed that the remnant M. modiolus populations are largely self-recruiting with little connectivity between them. The majority of larvae settled near the sources and movement was largely dependent on the tides and not influenced by wind or waves. Higher reef elevation resulted in larvae being able to disperse further away from the release point. However, larval numbers away from the source population are likely to be too low for successful recruitment. There was also little connectivity between the Irish Sea and Strangford Lough as any larvae entering the Lough remained predominantly in the Strangford Narrows. The areas covered by these self-seeding populations are suitable for M. modiolus translocation according to the MAXENT model. As a result of this work and in conjunction with other field work we propose a combination of total protection of all remaining larval sources and small scale translocations onto suitable substrata in each of the identified self-recruiting areas.

Design of engineered reflectors for radar cross section modification

A technique is proposed for the design of engineered reflectors consisting of doubly periodic arrays printed on thin grounded dielectric substrates that reflect an incoming wave from a given incoming direction to a predetermined outgoing direction. The proposed technique is based on a combination of Floquet theory for propagation in periodic structures and reflect-array principles. A flat surface designed to reflect a TE polarized wave incident at 45 back in the direction of the impinging signal at 14.7 GHz is employed as an example. By means of full-wave simulations, it is demonstrated that the monostatic RCS of a finite reflector is comparable with the specular RCS of a metallic mirror of the same dimensions. It is further shown that comparably high monostatic RCS values are obtained for angles of incidence in the 30-60 range, which are frequency dependent and thus open opportunities for target localization. A prototype array is fabricated and experimentally tested for validation. The proposed solution can be used to modify the radar cross section of a target. Other potential applications are also discussed. © 1963-2012 IEEE.

The biology of habitat dominance; can microbes behave as weeds?

Competition between microbial species is a product of, yet can lead to a reduction in, the microbial diversity of specific habitats. Microbial habitats can resemble ecological battlefields where microbial cells struggle to dominate and/or annihilate each other and we explore the hypothesis that (like plant weeds) some microbes are genetically hard-wired to behave in a vigorous and ecologically aggressive manner. These 'microbial weeds' are able to dominate the communities that develop in fertile but uncolonized - or at least partially vacant - habitats via traits enabling them to out-grow competitors; robust tolerances to habitat-relevant stress parameters and highly efficient energy-generation systems; avoidance of or resistance to viral infection, predation and grazers; potent antimicrobial systems; and exceptional abilities to sequester and store resources. In addition, those associated with nutritionally complex habitats are extraordinarily versatile in their utilization of diverse substrates. Weed species typically deploy multiple types of antimicrobial including toxins; volatile organic compounds that act as either hydrophobic or highly chaotropic stressors; biosurfactants; organic acids; and moderately chaotropic solutes that are produced in bulk quantities (e.g. acetone, ethanol). Whereas ability to dominate communities is habitat-specific we suggest that some microbial species are archetypal weeds including generalists such as: Pichia anomala, Acinetobacter spp. and Pseudomonas putida; specialists such as Dunaliella salina, Saccharomyces cerevisiae, Lactobacillus spp. and other lactic acid bacteria; freshwater autotrophs Gonyostomum semen and Microcystis aeruginosa; obligate anaerobes such as Clostridium acetobutylicum; facultative pathogens such as Rhodotorula mucilaginosa, Pantoea ananatis and Pseudomonas aeruginosa; and other extremotolerant and extremophilic microbes such as Aspergillus spp., Salinibacter ruber and Haloquadratum walsbyi. Some microbes, such as Escherichia coli, Mycobacterium smegmatis and Pseudoxylaria spp., exhibit characteristics of both weed and non-weed species. We propose that the concept of nonweeds represents a 'dustbin' group that includes species such as Synodropsis spp., Polypaecilum pisce, Metschnikowia orientalis, Salmonella spp., and Caulobacter crescentus. We show that microbial weeds are conceptually distinct from plant weeds, microbial copiotrophs, r-strategists, and other ecophysiological groups of microorganism. Microbial weed species are unlikely to emerge from stationary-phase or other types of closed communities; it is open habitats that select for weed phenotypes. Specific characteristics that are common to diverse types of open habitat are identified, and implications of weed biology and open-habitat ecology are discussed in the context of further studies needed in the fields of environmental and applied microbiology.

Controlled spillover in a single catalyst pellet: Rate modification, mechanism and relationship with electrochemical promotion

The effect of spillover processes on the activity of a catalyst system consisting of a mixed oxygen ion and electronic conducting support La0.6Sr0.4Co0.2Fe0.8O3d and a metal catalyst (Pt) were investigated. Two types of model single-pellet catalysts were used employing Pt deposited on both sides of a dense LSCF disc pellet. One of these single pellets employed highly disperse, physically non-continuous Pt, in contrast to studies on electrochemical promotion, while the other used a low dispersion continuous film. Driving forces for promoter migration were controlled through the manipulation of the oxygen chemical potential difference across the membrane. Catalyst rate modification was observed in all cases. However, it was found that there is a complex relationship between the rate modification, the driving forces for spillover and the geometrical arrangement of the catalyst on the support (i.e. catalyst dispersion).

Phosphoethanolamine modification of lipid A in colistin-resistant variants of Acinetobacter baumannii mediated by the pmrAB two-component regulatory system

Colistin resistance is rare in Acinetobacter baumannii, and little is known about its mechanism. We investigated the role of PmrCAB in this trait, using (i) resistant and susceptible clinical strains, (ii) laboratory-selected mutants of the type strain ATCC 19606 and of the clinical isolate ABRIM, and (iii) a susceptible/resistant pair of isogenic clinical isolates, Ab15/133 and Ab15/132, isolated from the same patient. pmrAB sequences in all the colistin-susceptible isolates were identical to reference sequences, whereas resistant clinical isolates harbored one or two amino acid replacements variously located in PmrB. Single substitutions in PmrB were also found in resistant mutants of strains ATCC 19606 and ABRIM and in the resistant clinical isolate Ab15/132. No mutations in PmrA or PmrC were found. Reverse transcriptase (RT)-PCR identified increased expression of pmrA (4- to 13-fold), pmrB (2- to 7-fold), and pmrC (1- to 3-fold) in resistant versus susceptible organisms. Matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry showed the addition of phosphoethanolamine to the hepta-acylated form of lipid A in the resistant variants and in strain ATCC 19606 grown under low-Mg induction conditions. pmrB gene knockout mutants of the colistin-resistant ATCC 19606 derivative showed >100-fold increased susceptibility to colistin and 5-fold decreased expression of pmrC; they also lacked the addition of phosphoethanolamine to lipid A. We conclude that the development of a moderate level of colistin resistance in A. baumannii requires distinct genetic events, including (i) at least one point mutation in pmrB, (ii) upregulation of pmrAB, and (iii) expression of pmrC, which lead to addition of phosphoethanolamine to lipid A. Copyright © 2011, American Society for Microbiology. All Rights Reserved.