Influence of pH and protein ChePep on motility of Helicobacter pylori
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The gastric disease-causing bacteria, Helicobacter pylori utilize flagella driven motility and chemotaxis to detect external acidic signal as they cross the pH gradient in the viscoelastic, gel-like mucus layer. The first part of this work explores the effects of pH on H. pylori’s motility in both culture broth (BB10) and porcine gastric mucin (PGM). In the human stomach there is a pH gradient across the gastric mucus layer, varying from pH 2 on the luminal surface to pH 7 on the epithelial surface. Both the flagellar motor and viscoelastic properties of medium depend on the pH, thus the change of motility of H. pylori across a pH gradient is complicated. The data from experiments performed by Dr. C. Su of the Bansil lab were analyzed and torque was calculated using resistive force theory (RFT). The results indicated that decreasing pH leads to decreased fraction of motile trajectories and mainly impacts the high end of distributions of swimming speeds and length of trajectories. At all pH’s the bacteria swim faster and have longer trajectory lengths in BB10 as compared to PGM. While bacteria are stuck in PGM gels at low pH’s, they swim at low pH in broth, albeit with reduced speed. The body rotation rate and estimated cell body torque are weakly dependent on pH in BB10, whereas in PGM the bacteria stuck in the low pH gel rotate faster than the motile bacteria leading to increased torque below pH 4. The second part of this thesis explores the influence of the protein ChePep on the motility on H. pylori. Based on the movies recorded by Dr. M.Constantino also of the Bansil lab, a detailed motility comparison and torque estimation between wild type (WT) H. pylori and a mutant lacking ChePep (ΔChePep) were performed. The mutant ΔChePep shows higher reversal frequency but similar rotation rate as compared with WT. The drastic increase of reversal frequency in ΔChePep reveals the malfunction of chemotaxis system of ΔChePep whose flagellar rotation are over-active.