ADM-like Hamiltonian formulation of gravity in the teleparallel geometry

We present a new Hamiltonian formulation of the Teleparallel Equivalent of General Relativity (TEGR) meant to serve as the departure point for canonical quantization of the theory. TEGR is considered here as a theory of a cotetrad field on a spacetime. The Hamiltonian formulation is derived by means of an ADM-like 3+1 decomposition of the field and without any gauge fixing. A complete set of constraints on the phase space and their algebra are presented. The formulation is described in terms of differential forms.Comment: 43 pages, LaTeX2e; the original 73 page paper arXiv:1111.5498v1 was revised and divided into two parts. The present paper is the first part of the original one (the second part is available as arXiv:1309.4685

Phenotypic Variation and Bistable Switching in Bacteria

Microbial research generally focuses on clonal populations. However, bacterial cells with identical genotypes frequently display different phenotypes under identical conditions. This microbial cell individuality is receiving increasing attention in the literature because of its impact on cellular differentiation, survival under selective conditions, and the interaction of pathogens with their hosts. It is becoming clear that stochasticity in gene expression in conjunction with the architecture of the gene network that underlies the cellular processes can generate phenotypic variation. An important regulatory mechanism is the so-called positive feedback, in which a system reinforces its own response, for instance by stimulating the production of an activator. Bistability is an interesting and relevant phenomenon, in which two distinct subpopulations of cells showing discrete levels of gene expression coexist in a single culture. In this chapter, we address techniques and approaches used to establish phenotypic variation, and relate three well-characterized examples of bistability to the molecular mechanisms that govern these processes, with a focus on positive feedback.

Justification for the use of Ocimum gratissimum L in herbal medicine and its interaction with disc antibiotics

<p>Abstract</p> <p>Background</p> <p>The ethanolic extract of the leaves of <it>Ocimium gratisimum </it>L. (Lamiaceae), used in traditional medicine for the treatment of several ailments such as urinary tract, wound, skin and gastrointestinal infections, was evaluated for its antibacterial properties against four clinical bacteria isolates namely: <it>Escherichia coli, Proteus mirabilis, Staphylococcus aureus and Pseudomonas aeruginosa </it>and the antifungal properties using a clinical isolate of <it>Candida albicans</it>. A typed bacterium of <it>Escherichia coli </it>ATCC 11775 and another typed fungal strain of <it>Candida albicans </it>(ATCC 90028) were also included. The study also intended to verify if the concomitant administration of conventional antibiotics with <it>Ocimium gratisimum </it>which is normally taken as food (spice) will negatively affect its activity.</p> <p>Methods</p> <p>The agar diffusion method was used to test the in vitro activity of the plant extract. The interaction of the plant extract with some disc antibiotics namely: ciprofloxacin, septrin, streptomycin, ampicillin, nystatin and ketoconazole was tested using the agar overlay inoculum susceptibility disc method. Phytochemical analysis of the extract was performed following established methods.</p> <p>Results</p> <p>The extract showed good but varying <it>in vitro </it>activities against all the isolates tested. While ampicillin showed synergistic interaction with the plant extract against clinical isolates of <it>E. coli </it>and <it>P. mirabilis</it>, septrin was synergistic against the clinical isolate of <it>E. coli </it>only. Similarly, the activity of the extract against <it>C. albicans </it>isolate was synergistic with ketoconazole and nystatin.</p> <p>Conclusion</p> <p>The study has validated the folkloric use of <it>O. gratissimum </it>in traditional medicinal practice and goes further to show that the use of this plant material as food spice may not really threaten the efficacy of some conventional antibiotics that may have been taken concomitantly with it as is the popular belief in the practice of herbal medicine in local/rural communities of many countries in the world.</p

Binding Site Alteration Is Responsible for Field-Isolated Resistance to Bacillus thuringiensis Cry2A Insecticidal Proteins in Two Helicoverpa Species

Background Evolution of resistance by target pests is the main threat to the long-term efficacy of crops expressing Bacillus thuringiensis (Bt) insecticidal proteins. Cry2 proteins play a pivotal role in current Bt spray formulations and transgenic crops and they complement Cry1A proteins because of their different mode of action. Their presence is critical in the control of those lepidopteran species, such as Helicoverpa spp., which are not highly susceptible to Cry1A proteins. In Australia, a transgenic variety of cotton expressing Cry1Ac and Cry2Ab (Bollgard II) comprises at least 80% of the total cotton area. Prior to the widespread adoption of Bollgard II, the frequency of alleles conferring resistance to Cry2Ab in field populations of Helicoverpa armigera and Helicoverpa punctigera was significantly higher than anticipated. Colonies established from survivors of F2 screens against Cry2Ab are highly resistant to this toxin, but susceptible to Cry1Ac. Methodology/Principal Findings Bioassays performed with surface-treated artificial diet on neonates of H. armigera and H. punctigera showed that Cry2Ab resistant insects were cross-resistant to Cry2Ae while susceptible to Cry1Ab. Binding analyses with 125I-labeled Cry2Ab were performed with brush border membrane vesicles from midguts of Cry2Ab susceptible and resistant insects. The results of the binding analyses correlated with bioassay data and demonstrated that resistant insects exhibited greatly reduced binding of Cry2Ab toxin to midgut receptors, whereas no change in 125I-labeled-Cry1Ac binding was detected. As previously demonstrated for H. armigera, Cry2Ab binding sites in H. punctigera were shown to be shared by Cry2Ae, which explains why an alteration of the shared binding site would lead to cross-resistance between the two Cry2A toxins. Conclusion/Significance This is the first time that a mechanism of resistance to the Cry2 class of insecticidal proteins has been reported. Because we found the same mechanism of resistance in multiple strains representing several field populations, we conclude that target site alteration is the most likely means that field populations evolve resistance to Cry2 proteins in Helicoverpa spp. Our work also confirms the presence in the insect midgut of specific binding sites for this class of proteins. Characterizing the Cry2 receptors and their mutations that enable resistance could lead to the development of molecular tools to monitor resistance in the [email protected]; [email protected]

The Regulatory Network of Natural Competence and Transformation of Vibrio cholerae

The human pathogen Vibrio cholerae is an aquatic bacterium frequently encountered in rivers, lakes, estuaries, and coastal regions. Within these environmental reservoirs, the bacterium is often found associated with zooplankton and more specifically with their chitinous exoskeleton. Upon growth on such chitinous surfaces, V. cholerae initiates a developmental program termed “natural competence for genetic transformation.” Natural competence for transformation is a mode of horizontal gene transfer in bacteria and contributes to the maintenance and evolution of bacterial genomes. In this study, we investigated competence gene expression within this organism at the single cell level. We provide evidence that under homogeneous inducing conditions the majority of the cells express competence genes. A more heterogeneous expression pattern was observable on chitin surfaces. We hypothesize that this was the case due to the heterogeneity around the chitin surface, which might vary extensively with respect to chitin degradation products and autoinducers; these molecules contribute to competence induction based on carbon catabolite repression and quorum-sensing pathways, respectively. Therefore, we investigated the contribution of these two signaling pathways to natural competence in detail using natural transformation assays, transcriptional reporter fusions, quantitative RT–PCR, and immunological detection of protein levels using Western blot analysis. The results illustrate that all tested competence genes are dependent on the transformation regulator TfoX. Furthermore, intracellular cAMP levels play a major role in natural transformation. Finally, we demonstrate that only a minority of genes involved in natural transformation are regulated in a quorum-sensing-dependent manner and that these genes determine the fate of the surrounding DNA. We conclude with a model of the regulatory circuit of chitin-induced natural competence in V. cholerae

Conservation of energy-momentum of matter as the basis for the gauge theory of gravitation

According to Yang \& Mills (1954), a {\it conserved} current and a related rigid (`global') symmetry lie at the foundations of gauge theory. When the rigid symmetry is extended to a {\it local} one, a so-called gauge symmetry, a new interaction emerges as gauge potential $A$; its field strength is $F\sim {\rm curl} A$. In gravity, the conservation of the energy-momentum current of matter and the rigid translation symmetry in the Minkowski space of special relativity lie at the foundations of a gravitational gauge theory. If the translation invariance is made local, a gravitational potential $\vartheta$ arises together with its field strength $T\sim {\rm curl}\,\vartheta$. Thereby the Minkowski space deforms into a Weitzenb\"ock space with nonvanishing torsion $T$ but vanishing curvature. The corresponding theory is reviewed and its equivalence to general relativity pointed out. Since translations form a subgroup of the Poincar\'e group, the group of motion of special relativity, one ought to straightforwardly extend the gauging of the translations to the gauging of full Poincar\'e group thereby also including the conservation law of the {\it angular momentum} current. The emerging Poincar\'e gauge (theory of) gravity, starting from the viable Einstein-Cartan theory of 1961, will be shortly reviewed and its prospects for further developments assessed.Comment: 46 pages, 4 figures, minor corrections, references added, contribution to "One Hundred Years of Gauge Theory" edited by S. De Bianchi and C. Kiefe