Mutagenic studies into the catalytic versatility of soluble methane monooxygenase

Soluble methane monooxygenase (sMMO) is a multicomponent bacterial enzyme that catalyzes the oxidation of methane to methanol, as well as oxidizing many other adventitious substrates. A number of mutagenic studies were carried out on the sMMO enzyme of Methylosinus trichosporium OB3b in order to gain insight into sMMO and probe how structural aspects relate to function of the enzyme. Leu110 within the hydroxylase a-subunit of sMMO has been proposed as a possible gating residue, controlling access of substrate to the active site (Rosenzweig et al. 1997). A range of site directed mutants were created at the 110 position and screened for activity with a number of aromatic substrates. All mutants showed relaxed regioselectivity with all substrates assayed. However no evidence of a gating residue was found, indicating that Leu110 is more important in determining regioselectivity than substrate access to the active site. Comparison to the highly similar butane monooxygenase led to the creation of three site directed mutants: M184V F282L and C151T. M184V and C151T showed small changes in regioselectivity and reduced activity with most substrates. The M184V mutant showed relaxed regioselectivity and a novel oxidation product with the substrate mesitylene which may have implications for substrate trafficking. The F282L mutant produced a stable enzyme which had no activity with any of the substrates tested, showing Phe282 is important for the enzyme function. A random mutagenesis experiment was devised and a colorimetric screen for the oxidation of triaromatic compounds was used to screen mutant libraries for activity towards anthracene and phenanthrene. However no activity towards triaromatic compounds was detected. In order to improve the cloning strategies and to make creation of mutant libraries easier, a novel expression vector pT2ML was created. The pT2ML vector reduces the number of cloning steps required to make soluble methane monooxygenase mutants. This expression system was used to make a site directed mutants F188Aand N116G in order to complement previous site directed mutant studies, as well as a recombinant wild type mutant in order to asses the activity of the new expression system which is comparible to the wild type enzyme

Temocillin: a new candidate antibiotic for local antimicrobial delivery in orthopaedic surgery?

Objectives - To assess the performance of the Gram-negative-specific antibiotic temocillin in polymethylmethacrylate bone cement pre-loaded with gentamicin, as a strategy for local antibiotic delivery. Methods - Temocillin was added at varying concentrations to commercial gentamicin-loaded bone cement. The elution of the antibiotic from cement samples over a 2 week period was quantified by LC-MS. The eluted temocillin was purified by fast protein liquid chromatography and the MICs for a number of antibiotic-resistant Escherichia coli were determined. The impact strength of antibiotic-loaded samples was determined using a Charpy-type impact testing apparatus. Results - LC-MS data showed temocillin eluted to clinically significant concentrations within 1 h in this laboratory system and the eluted temocillin retained antimicrobial activity against all organisms tested. Impact strength analysis showed no significant difference between cement samples with or without temocillin. Conclusions - Temocillin can be added to bone cement and retains its antimicrobial activity after elution. The addition of up to 10% temocillin did not affect the impact strength of the cement. The results show that temocillin is a promising candidate for use in antibiotic-loaded bone cement.</p

Mechanistic Insight into the Early Stages of Toroidal Pore Formation by the Antimicrobial Peptide Smp24

The antimicrobial peptide Smp24, originally derived from the venom of Scorpio maurus palmatus, is a promising candidate for further drug development. However, before doing so, greater insight into the mechanism of action is needed to construct a reliable structure–activity relationship. The aim of this study was to specifically investigate the critical early stages of peptide-induced membrane disruption. Single-channel current traces were obtained via planar patch-clamp electrophysiology, with multiple types of pore-forming events observed, unlike those expected from the traditional, more rigid mechanistic models. To better understand the molecular-level structures of the peptide-pore assemblies underlying these observed conductance events, molecular dynamics simulations were used to investigate the peptide structure and orientation both before and during pore formation. The transition of the peptides to transmembrane-like states within disordered toroidal pores occurred due to a peptide-induced bilayer-leaflet asymmetry, explaining why pore stabilization does not always follow pore nucleation in the experimental observations. To fully grasp the structure–activity relationship of antimicrobial peptides, a more nuanced view of the complex and dynamic mechanistic behaviour must be adopted

Gemini surfactant as multifunctional corrosion and biocorrosion inhibitors for mild steel

Biocorrosion is an important type of corrosion which leads to economic losses across oil and gas industries, due to increased monitoring, maintenance, and a reduction in platform availability. Ideally, a chemical compound engineered to mitigate against biocorrosion would possess both antimicrobial properties, as well as efficient corrosion inhibition. Gemini surfactants have shown efficacy in both of these properties, however there still remains a lack of electrochemical information regarding biocorrosion inhibition. The inhibition of corrosion and biocorrosion, by cationic gemini surfactants, of carbon steel was investigated. The results showed that the inhibition efficiency of the gemini surfactants was high (consistently >95%), even at low concentrations. Gemini surfactants also showed strong antimicrobial activity, with a minimum inhibitory concentration (0.018 mM). Corrosion inhibition was investigated by electrochemical impedance spectroscopy (EIS) and linear polarisation resistance (LPR), with biocorrosion experiments carried out in an anaerobic environment. Surface morphology was analysed using scanning electron microscopy (SEM)

Spatial epidemiological patterns suggest mechanisms of land-sea transmission for Sarcocystis neurona in a coastal marine mammal.

Sarcocystis neurona was recognised as an important cause of mortality in southern sea otters (Enhydra lutris nereis) after an outbreak in April 2004 and has since been detected in many marine mammal species in the Northeast Pacific Ocean. Risk of S. neurona exposure in sea otters is associated with consumption of clams and soft-sediment prey and is temporally associated with runoff events. We examined the spatial distribution of S. neurona exposure risk based on serum antibody testing and assessed risk factors for exposure in animals from California, Washington, British Columbia and Alaska. Significant spatial clustering of seropositive animals was observed in California and Washington, compared with British Columbia and Alaska. Adult males were at greatest risk for exposure to S. neurona, and there were strong associations with terrestrial features (wetlands, cropland, high human housing-unit density). In California, habitats containing soft sediment exhibited greater risk than hard substrate or kelp beds. Consuming a diet rich in clams was also associated with increased exposure risk. These findings suggest a transmission pathway analogous to that described for Toxoplasma gondii, with infectious stages traveling in freshwater runoff and being concentrated in particular locations by marine habitat features, ocean physical processes, and invertebrate bioconcentration

Family Caregivers' Experiences of Involuntary Psychiatric Hospital Admissions of Their Relatives – a Qualitative Study

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Peering down the sink: a review of isoprene metabolism by bacteria.

Isoprene (2-methyl-1,3-butadiene) is emitted to the atmosphere each year in sufficient quantities to rival methane (>500 Tg C yr-1 ), primarily due to emission by trees and other plants. Chemical reactions of isoprene with other atmospheric compounds, such as hydroxyl radicals and inorganic nitrogen species (NOx ), have implications for global warming and local air quality, respectively. For many years, it has been estimated that soil-dwelling bacteria consume a significant amount of isoprene (~20 Tg C yr-1 ), but the mechanisms underlying the biological sink for isoprene have been poorly understood. Studies have indicated or confirmed the ability of diverse bacterial genera to degrade isoprene, whether by the canonical iso-type isoprene degradation pathway or through other less well-characterised mechanisms. Here, we review current knowledge of isoprene metabolism and highlight key areas for further research. In particular, examples of isoprene-degraders which do not utilise the isoprene monooxygenase have been identified in recent years. This has fascinating implications both for the mechanism of isoprene uptake by bacteria, but also for the ecology of isoprene-degraders in the environments