Mechanistic insight from thermal activation parameters for oxygenation reactions of different substrates with biomimetic iron porphyrin models for compounds I and II

Compound I, an oxo–iron(IV) porphyrin π-cation radical species, and its one-electron-reduced form compound II are regarded as key intermediates in reactions catalyzed by cytochrome P450. Although both reactive intermediates can be easily produced from model systems such as iron(III) meso-tetra(2,4,6-trimethylphenyl)porphyrin hydroxide by selecting appropriate reaction conditions, there are only a few thermal activation parameters reported for the reactions of compound I analogues, whereas such parameters for the reactions of compound II analogues have not been investigated so far. Our study demonstrates that ΔH ^≠ and ΔS ^≠ are closely related to the chemical nature of the substrate and the reactive intermediate (viz., compounds I and II) in epoxidation and C–H abstraction reactions. Although most studied reactions appear to be enthalpy-controlled (i.e., ΔH ^≠ > −TΔS ^≠), different results were found for C–H abstractions catalyzed by compound I. Whereas the reaction with 9,10-dihydroanthracene as a substrate is also dominated by the activation enthalpy (ΔH ^≠ = 42 kJ/mol, ΔS ^≠ = 41 J/Kmol), the same reaction with xanthene shows a large contribution from the activation entropy (ΔH ^≠ = 24 kJ/mol, ΔS ^≠ = −100 J/kmol). This is of special interest since the activation barrier for entropy-controlled reactions shows a significant dependence on temperature, which can have an important impact on the relative reaction rates. As a consequence, a close correlation between bond strength and reaction rate—as commonly assumed for C–H abstraction reactions—no longer exists. In this way, this study can contribute to a proper evaluation of experimental and computational data, and to a deeper understanding of mechanistic aspects that account for differences in the reactivity of compounds I and II.     

Identification of fitness determinants in Enterococcus faecalis by differential proteomics

Enterococcus (E.) faecalis is found as commensal in healthy humans, in a variety of fermented foods. It can serve as probiotic but also as pathogen causing endocarditis, bacteremia and urinary tract infections. We have employed a proteomic study with E. faecalis strain OG1RF under different growth conditions and in contact to mouse intestinal cells to identify novel latent and adaptive fitness determinants. These relate to changes in catabolic pathways (BudA), protein biosynthesis (AsnS), cellular surface biosynthesis (RmlA) and regulatory mechanisms (OmpR). This knowledge can be used to derive novel evidence-based targets, which can be used to further elucidate gene expression changes enhancing pathogenicity or fitness in a commensal strain and possibly delineate this species into groups of higher and lower risk for applications in a food or a medical context versus improved treatment strategies of the so far hard to cure diseases.     

The influence of tree canopies and elephants on sub-canopy vegetation in a savannah

The apparent influence of elephants on the structure of savannahs in Africa may be enhanced by management activities, fire and other herbivores. We separated the effect elephants have on grasses, woody seedlings (<0.5 m) and saplings (0.5–2 m) from the effect of tree canopies (canopy effect), and herbivory (park effect). We defined the canopy effect as the differences between plant abundances and diversity indices under tree canopies and 20 m away from these. Our testing of the park effect relied on the differences in the sub-canopy plant indices inside and outside a protected area that supported a range of herbivores. We based our assessment of the elephant effect on sub-canopy vegetation indices associated with elephant induced reductions in tree canopies. The park and canopy effects were more pronounced than the elephant effect. The park effect suppressed the development of woody seedlings into saplings. Conditions associated with tree canopies benefited woody plants, but not the grasses, as their indices were lower under trees. Elephants reducing canopies facilitated grass species tolerant of direct solar radiation. We concluded that management should consider other agents operating in the system when deciding on reducing the impact that elephants may have on vegetation.     

Ratios between Alpha-, Beta- and Gamma-proteobacteria in tap water determined by the ProteoQuant assay

Aims:  Proteobacteria are widespread on earth. Recently, it has been discovered that a diverse repertoire of proteobacteria are also dominant in tap water. It is therefore important to use high-throughput monitoring tools for tap water. Here, the high-throughput assay ProteoQuant was developed to quantify the main proteobacterial phyla in tap water.
Methods and Results:  The principle of ProteoQuant is proteobacterial-selective 23S rRNA gene PCR amplification, with multiple competitive TaqMan probes for quantifying the phyla Alpha-, Beta - and Gamma-proteobacteria. The ProteoQuant assay was evaluated, analysing both designed proteobacterial mixes and rRNA gene clone libraries from tap water. These evaluations showed a good coverage and accuracy of the ProteoQuant assay.
Conclusions:  Large-scale tap water screening using ProteoQuant revealed a dominance of Beta-proteobacteria and a potential interaction between Alpha - and Beta-proteobacteria. Gamma-proteobacteria , on the other hand, seemed independent of the two other phyla.
Significance and Impact of the Study:  The ProteoQuant assay will potentially be important for future understanding of the ecological forces shaping the tap water microbiota.     

Fungal ferritins: The ferritin from mycelia of Absidia spinosa is a bacterioferritin

Two distinct ferritin like iron containing proteins have been identified and isolated from the fungus Absidia spinosa; one from the spores and another from the mycelia. The mycelial protein has been purified and consists of two subunits of approx. 20 kDa. The N-terminal sequences of both subunits have been determined. The holoprotein as isolated contains approx. 750 iron atoms/molecule and exhibits a heme-like UV-Vis spectrum. Based on the heme spectrum and the high degree of sequence homology found, it has been established that the mycelial protein is a bacterioferritin. This is the first example demonstrating the presence of a bacterioferritin in a eukaryotic organism.