14,918 research outputs found
Caulobacter crescentus adapts to phosphate starvation by synthesizing anionic glycoglycerolipids and a novel glycosphingolipid
No full textCaulobacter crescentus adapts to phosphate starvation by elongating its cell body and a polar stalk structure. The stalk is an extension of the Gram-negative envelope containing inner and outer membranes as well as a peptidoglycan cell wall. Cellular elongation requires a 6- to 7-fold increase in membrane synthesis, yet phosphate limitation would preclude the incorporation of additional phospholipids. In the place of phospholipids, C. crescentus can synthesize several glycolipid species, including a novel glycosphingolipid (GSL-2). While glycosphingolipids are ubiquitous in eukaryotes, the presence of GSL-2 in C. crescentus is surprising since GSLs had previously been found only in Sphingomonas species, in which they play a role in outer membrane integrity. In this paper, we identify three proteins required for GSL-2 synthesis: CcbF catalyzes the first step in ceramide synthesis, while Sgt1 and Sgt2 sequentially glycosylate ceramides to produce GSL-2. Unlike in Sphingomonas, GSLs are nonessential in C. crescentus; however, the presence of ceramides does contribute to phage resistance and susceptibility to the cationic antimicrobial peptide polymyxin B. The identification of a novel lipid species specifically produced upon phosphate starvation suggests that bacteria may be able to synthesize a wider variety of lipids in response to stresses than previously observed. Uncovering these lipids and their functional relevance will provide greater insight into microbial physiology and environmental adaptation.Peer reviewe
Perspective: Adhesion Mediated Signal Transduction in Bacterial Pathogens
No full textDuring the infection process, pathogenic bacteria undergo large-scale transcriptional changes to promote virulence and increase intrahost survival. While much of this reprogramming occurs in response to changes in chemical environment, such as nutrient availability and pH, there is increasing evidence that adhesion to host-tissue can also trigger signal transduction pathways resulting in differential gene expression. Determining the molecular mechanisms of adhesion-mediated signaling requires disentangling the contributions of chemical and mechanical stimuli. Here we highlight recent work demonstrating that surface attachment drives a transcriptional response in bacterial pathogens, including uropathogenic Escherichia coli (E. coli), and discuss the complexity of experimental design when dissecting the specific role of adhesion-mediated signaling during infection.Peer reviewe
Differential modes of crosslinking establish spatially distinct regions of peptidoglycan in Caulobacter crescentus
No full textThe diversity of cell shapes across the bacterial kingdom reflects evolutionary pressures that have produced physiologically important morphologies. While efforts have been made to understand the regulation of some prototypical cell morphologies such as that of rod-shaped Escherichia coli, little is known about most cell shapes. For Caulobacter crescentus, polar stalk synthesis is tied to its dimorphic life cycle, and stalk elongation is regulated by phosphate availability. Based on the previous observation that C. crescentus stalks are lysozyme-resistant, we compared the composition of the peptidoglycan cell wall of stalks and cell bodies and identified key differences in peptidoglycan crosslinking. Cell-body peptidoglycan contained primarily DD-crosslinks between meso-diaminopimelic acid and D-alanine residues, whereas stalk peptidoglycan had more LD-transpeptidation (meso-diaminopimelic acid-meso-diaminopimelic acid), mediated by LdtD. We determined that ldtD is dispensable for stalk elongation; rather, stalk LD-transpeptidation reflects an aging process associated with low peptidoglycan turnover in the stalk. We also found that lysozyme resistance is a structural consequence of LD-crosslinking. Despite no obvious selection pressure for LD-crosslinking or lysozyme resistance in C. crescentus, the correlation between these two properties was maintained in other organisms, suggesting that DAP-DAP crosslinking may be a general mechanism for regulating bacterial sensitivity to lysozyme.Peer reviewe
Irradiation with visible light enhances the antibacterial toxicity of silver nanoparticles produced by laser ablation
No full textThe rise of antibiotic-resistant bacteria is a rapidly growing global health concern. According to the Center for Disease Control, approximately 2 million illnesses and 23,000 deaths per year occur in the USA due to antibiotic resistance. In recent years, there has been a surge in the use of metal nanoparticles as coatings for orthopedic implants, wound dressings, and food packaging, due to their antimicrobial properties. In this report, we demonstrate that the antibacterial efficacy of silver nanoparticles (AgNPs) is enhanced with exposure to light from the visible spectrum. We find that the increased toxicity is due to augmented silver ion release and bacterial uptake. Interestingly, silver ion toxicity does not appear to depend on the formation of reactive oxygen species. Our findings provide a novel paradigm for using light to regulate the toxicity of AgNPs which may have a significant impact in the development of new antimicrobial therapeutics.Peer reviewe
Antibacterial Properties of Nanoparticles: A Comparative Review of Chemically Synthesized and Laser-Generated Particles
No full textNanomaterials have recently received an enormous amount of attention from the scientific community due to their outstanding activity relative to bulk materials. This increase in activity relative to bulk materials can be attributed to the high surface area to volume ratio associated with nanoparticles. Nanoparticles have found applications in almost every field of science. Currently there is significant interest in the development of nanoparticles as antibacterial agents. This work is paramount due to the increasing number of antibiotic-resistant strains of bacteria. Nanoparticles can be synthesized using various methods, each with their own advantages and disadvantages, and the method is often chosen based on the intended application. This review will cover the most prevalent method, chemical-based reduction of salts, and a fairly new laser-based method that holds tremendous promise in nanoparticle synthesis. We conclude with a comparison of the antimicrobial activities of materials made via each method.Peer reviewe
Higher dimensional theories in physics, following the Kaluza model of unification
No full textThis thesis traces the origins and evolution of higher dimensional models in physics, with particular reference to the five-dimensional Kaluza-Klein unification. It includes the motivation needed, and the increasing status and significance of the multidimensional description of reality for the 1990's. The differing conceptualisations are analysed, from the mathematical, via Kasner's embedding dimensions and Schrodinger's waves, to the high status of Kaluza-Klein dimensions in physics today. This includes the use of models, and the metaphysical interpretations needed to translate the mathematics. The main area of original research is the unpublished manuscripts and letters of Theodor Kaiuza, some Einstein letters, further memoirs from his son Theodor Kaiuza Junior and from some of his original students. Unpublished material from Helsinki concerns the Finnish physicist Nordstrom, the real originator of the idea that 'forces' in 4-dimensional spacetime might arise from gravity in higher dimensions. The work of the Swedish physicist Oskar Klein and the reactions of de Broglie and Einstein initiated the Kaluza-Klein connection which is traced through fifty years of neglect to its re-entry into mainstream physics. The cosmological significance and conceptualisation through analogue models is charted by personal correspondence with key scientists across a range of theoretical physics, involving the use of aesthetic criteria where there is no direct physical verification. Qualitative models implicitly indicating multidimensions are identified in the paradoxes and enigmas of existing physics, in Quantum Mechanics and the singularities in General Relativity. The Kaluza-Klein philosophy brings this wide range of models together in the late 1980's via supergravity, superstrings and supermanifolds. This new multidimensional paradigm wave is seen to produce a coherent and consistent metaphysics, a new perspective on reality. It may also have immense potential significance for philosophy and theology. The thesis concludes with the reality question, "Are we a four-dimensional projection of a deeper reality of many, even infinite, dimensions?
tritrophic-dispersal-model: Code used for creating figures for "Non-hierarchical dispersal promotes stability and resilience in a tri-trophic metacommunity"
No full text<p>This is the commented code used for creating figures for the paper. Any questions regarding the code should be directed to the corresponding author and repository owner (Eric Pedersen). </p>
Q & A - Eric Davidson
No full textEric Davidson graduated from the University of Pennsylvania in 1954 and received his PhD from Rockefeller University in 1963. He remained at Rockefeller until 1971 when he moved to Caltech in Pasadena, California. He was elected to the U.S. National Academy of Sciences in 1985, and is at present Norman Chandler Professor of Cell Biology in the Division of Biology, Caltech. He is the author of 5 books and over 400 papers on developmental gene regulation and evolution of genomic programs for development. For the last decade his work has focused on theory and operation of developmental gene regulatory networks
Eric C. Lincoln, Professor of Sociology and Religion, 1971
No full textThis is an interview with Eric C. Lincoln. Eric was a Professor of Sociology and religion, Union Theological Seminary and author of many books and articles on Negro history. In this recording the contributors discuss local memphis politics, sociology, and race relations compared to that of other cities in the South and the rest of the country
- …
