Summary The helical shape of the human stomach pathogen Helicobacter pylori has been suggested to provide mechanical advantage for penetrating the viscous stomach mucus layer. Using single-cell tracking and quantitative morphology analysis we document marked variation in cell body helical parameters and flagellum number among H. pylori strains leading to distinct and broad speed distributions in broth and viscous gastric mucin media. These distributions reflect both temporal variation in swimming speed and morphologic variation within the population. Isogenic mutants with straight-rod morphology showed 7–21% reduction in speed and a lower fraction of motile bacteria. Mutational perturbation of flagellum number revealed a 19% increase in speed with 4 vs. 3 median flagellum number. Resistive force theory modeling incorporating variation of both cell shape and flagellum number predicts qualitative speed differences of 10–30% among strains. However, quantitative comparisons suggest RFT underestimates the influence of cell body shape on speed for helical shaped bacteria.
The bacterium Helicobacter pylori (H. pylori), has evolved to survive in the highly acidic environment of the stomach and colonize on the epithelial surface of the gastric mucosa. Its pathogenic effects are well known to cause gastritis, peptic ulcers, and gastric cancer. In order to infect the stomach and establish colonies on the mucus epithelial surface, the bacterium has to move across the gel-like gastric mucus lining of the stomach under acidic conditions. In this review we address the question of how the bacterium gets past the protective mucus barrier from a biophysical perspective. We begin by reviewing the molecular structure of gastric mucin and discuss the current state of understanding concerning mucin polymerization and low pH induced gelation. We then focus on the viscoelasticity of mucin in view of its relevance to the transport of particles and bacteria across mucus, the key first step in H. pylori infection. The second part of the review focuses on the motility of H. pylori in mucin solutions and gels, and how infection with H. pylori in turn impacts the viscoelastic properties of mucin. We present recent microscopic results tracking the motion of H. pylori in mucin solutions and gels. We then discuss how the biochemical strategy of urea hydrolysis required for survival in the acid is also relevant to the mechanism that enables flagella-driven swimming across the mucus gel layer. Other aspects of the influence of H. pylori infection such as, altering gastric mucin expression, its rate of production and its composition, and the influence of mucin on factors controlling H. pylori virulence and proliferation are briefly discussed with references to relevant literature.
the gastric ulcer and cancer causing bacteria, helicobacter Pylori have uniquely adapted to swim across the viscoelastic mucus gel that lines the stomach epithelial surface and colonize in the harsh acidic environment of the stomach. in this paper we first briefly review results of bacteria tracking and oscillatory shear rheology studies to suggest how the bacteria get across the viscoelastic mucus gel by using a chemical mechanism to raise the pH from acidic to neutral which also triggers a gel to sol transition of mucin. We then present new microrheology studies to show that the bacterium influences the Brownian motion of spherical tracer particles in culture broth solution and in solutions of gastric mucin. the elastic and viscous moduli obtained by tracking particles in the mucin solutions are found to decrease in the presence of bacteria. We also examined the Brownian motion of the bacteria themselves and find that motile bacteria display super-diffusive anomalous Brownian motion while the immotile bacteria exhibit regular diffusive Brownian motion.
To realize the promise of the Next Generation Science Standards, educators require new three-dimensional, phenomenon-based curriculum materials. We describe and report on pilot test results from such a resource-Evolution: DNA and the Unity of Life. Designed for the Next Generation Science Standards, this freely available unit was developed for introductory high school biology students. It builds coherent understanding of evolution over the course of seven to 8 weeks. Based around multiple phenomena, it includes core ideas about evolution, as well as pertinent core ideas from heredity. The unit integrates relevant crosscutting concepts as well as practice in analyzing and interpreting skill-level-appropriate data from published research, and constructing evidence-based arguments. We report results from a national pilot test involving 944 grade nine or ten students in 16 teachers' classrooms. Results show statistically significant gains with large effect sizes from pretest to posttest in students' conceptual understanding of evolution and genetics. Students also gained skill in identifying claims, evidence, and reasoning in scientific arguments.
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