The role of body rotation in bacterial flagellar bundling

In bacterial chemotaxis, E. coli cells drift up chemical gradients by a series of runs and tumbles. Runs are periods of directed swimming, and tumbles are abrupt changes in swimming direction. Near the beginning of each run, the rotating helical flagellar filaments which propel the cell form a bundle. Using resistive-force theory, we show that the counter-rotation of the cell body necessary for torque balance is sufficient to wrap the filaments into a bundle, even in the absence of the swirling flows produced by each individual filament

Twirling Elastica: Kinks, Viscous Drag, and Torsional Stress

Biological filaments such as DNA or bacterial flagella are typically curved in their natural states. To elucidate the interplay of viscous drag, twisting, and bending in the overdamped dynamics of such filaments, we compute the steady-state torsional stress and shape of a rotating rod with a kink. Drag deforms the rod, ultimately extending or folding it depending on the kink angle. For certain kink angles and kink locations, both states are possible at high rotation rates. The agreement between our macroscopic experiments and the theory is good, with no adjustable parameters.Comment: 4 pages, 4 figure

Predictors of recurrence and reoperation for prosthetic valve endocarditis after valve replacement surgery for native valve endocarditis

ObjectiveSurgical treatment of native valve endocarditis remains challenging, especially in cases with paravalvular destruction. Basic principles include complete debridement and reconstruction. This study is designed to evaluate the outcomes of surgical reconstruction of complex annular endocarditis using standard techniques and materials, including autologous and bovine pericardium.MethodsFrom 1975 to 2000, 358 cases (357 patients, mean age 49 ± 16 years, range 18–88 years) of native valve endocarditis were surgically managed. Bioprosthetic valves were implanted in 189 cases, and mechanical prostheses were implanted in 169 cases. A total of 78 cases of paravalvular destruction were identified: 62 annular abscesses, 8 fistulas, and 8 combined abscesses/fistulas. These were managed with 46 pericardial patches and 32 isolated suture reconstructions after radical debridement and prosthetic valve replacement.ResultsThe overall early mortality was 8.4% (n = 30). The mortality with paravalvular destruction was 17.9%, and the mortality with simple leaflet infection was 5.7% (P = .001). The unadjusted survival at 20 years was 26.4% ± 4.9% for bioprosthetic valves and 56.5% ± 8.1% for mechanical prostheses (P = .007). The freedom from recurrent prosthetic valve endocarditis was 78.9% ± 4.4% at 15 years. The freedom from reoperation for recurrent prosthetic valve endocarditis was 85.8% ± 4.2% at 15 years. The freedom from reoperation after reconstruction for paravalvular destruction was 88.2% ± 6.9% at 15 years. The freedom from mortality for recurrent prosthetic valve endocarditis was 92.7% ± 3.4% at 15 years. The independent predictors of reoperation were age (hazard ratio 0.930, P = .005) and intravenous drug use/human immunodeficiency virus plus surgical technique (hazard ratio 12.8, P = .003 for patch reconstruction plus valve and hazard ratio 3.6, P = .038 for valve replacement only). Prosthesis type was not predictive when separated from intravenous drug use/human immunodeficiency virus (hazard ratio 3.268, P = .088).ConclusionParavalvular destruction is associated with a higher operative mortality. Native valve endocarditis can be managed with reasonable long-term survival and low rates of reinfection with radical debridement and pericardial reconstruction with bioprostheses and mechanical prostheses. The type of prosthesis implanted does not influence long-term outcome. Patients with a history of intravenous drug use and human immunodeficiency virus are at increased risk for recurrent infection and reoperation

Twirling and Whirling: Viscous Dynamics of Rotating Elastica

Motivated by diverse phenomena in cellular biophysics, including bacterial flagellar motion and DNA transcription and replication, we study the overdamped nonlinear dynamics of a rotationally forced filament with twist and bend elasticity. Competition between twist injection, twist diffusion, and writhing instabilities is described by a novel pair of coupled PDEs for twist and bend evolution. Analytical and numerical methods elucidate the twist/bend coupling and reveal two dynamical regimes separated by a Hopf bifurcation: (i) diffusion-dominated axial rotation, or twirling, and (ii) steady-state crankshafting motion, or whirling. The consequences of these phenomena for self-propulsion are investigated, and experimental tests proposed.Comment: To be published in Physical Review Letter

Ten years of major equestrian injury: are we addressing functional outcomes?

YesFunding provided by the Open Access Authors Fund

Overview of mathematical approaches used to model bacterial chemotaxis I: the single cell

Mathematical modeling of bacterial chemotaxis systems has been influential and insightful in helping to understand experimental observations. We provide here a comprehensive overview of the range of mathematical approaches used for modeling, within a single bacterium, chemotactic processes caused by changes to external gradients in its environment. Specific areas of the bacterial system which have been studied and modeled are discussed in detail, including the modeling of adaptation in response to attractant gradients, the intracellular phosphorylation cascade, membrane receptor clustering, and spatial modeling of intracellular protein signal transduction. The importance of producing robust models that address adaptation, gain, and sensitivity are also discussed. This review highlights that while mathematical modeling has aided in understanding bacterial chemotaxis on the individual cell scale and guiding experimental design, no single model succeeds in robustly describing all of the basic elements of the cell. We conclude by discussing the importance of this and the future of modeling in this area

Protecting Wild Land from Wind Farms in a Post-EU Scotland

Scotland is one of the places in Europe to have experienced significant wind farm development over recent years. Concern about impacts on wild land has resulted in legal challenges based on European Union (EU) law. This article analyses whether wild land can be protected from wind farms and the differences that the United Kingdom (UK) departure from the EU will make. It considers the concept of 'wild land' compared with 'wilderness', analyses the legal basis (if any) for wild land protection, and examines potential impacts from wind farms. It highlights the significance of EU environmental law, particularly nature conservation and environmental assessment law, and analyses recent Scottish jurisprudence that has applied this. The role of the European Commission and Court of Justice of the EU (CJEU) is emphasised as a key part of EU environmental law. The article asks whether relevant global and regional environmental agreements can effectively replace the content of the substantive law and context of the Commission and CJEU. Four environmental agreements and two related compliance procedures are briefly evaluated. The conclusion is that while EU law does not directly provide protection for wild land, it is considerably stronger than the international environmental agreements that may replace it

Overview of mathematical approaches used to model bacterial chemotaxis II: bacterial populations

We review the application of mathematical modeling to understanding the behavior of populations of chemotactic bacteria. The application of continuum mathematical models, in particular generalized Keller–Segel models, is discussed along with attempts to incorporate the microscale (individual) behavior on the macroscale, modeling the interaction between different species of bacteria, the interaction of bacteria with their environment, and methods used to obtain experimentally verified parameter values. We allude briefly to the role of modeling pattern formation in understanding collective behavior within bacterial populations. Various aspects of each model are discussed and areas for possible future research are postulated