# Single Cell Chemotactic Responses of
## 3 Results and Discussion
### Impact of Urea on the Type and Frequency of H. pylori Movements  
The cell dynamics and mechanics of _H. pylori_ during motility in chemotaxis buffer were also characterized by analyzing the video recorded by the microscope at slower acquisition recording rates. Most bacterial cells exhibited twirling and tumbling behavior in chemotaxis buffer. Figure 3 gives an example of the typical motility behavior of a single cell. Three dimensional rotations were observed, as indicated by arrows shown in the images. Figure 1: Cellular velocity of the single _Helicobacter pylori_ bacteria in chemotaxis buffer with 10 and 100 mM urea within the microfluidic device. An obvious drop was observed between baseline and 10 or 100 mM urea-exposed cells. Three independent tests were conducted and 20–30 bacteria in each test were randomly selected for tracking and analyzing in each test. Figure 2: Directness of the _H. pylori_ in chemotaxis buffer with 10 and 100 mM of urea within the microfluidic device. A steep decrease was observed in the directness when urea solution was introduced, while no significant differences were observed between 10 and 100 mM urea-exposed cells. Three independent tests were conducted and 20–30 bacteria in each test were randomly selected for tracking and analyzing in each test. The chemotactic behavior of _H. pylori_, dictated by flagellar locomotion, is a crucial factor in the bacterial colonization process [19]. _H. pylori_ cells normally have 2-6 sheathed flagella that the bacterium uses to move to and within its ecological niche. The _H. pylori_ flagella consist of three structural components: a basal body, an external helically shaped filament, and a hook. These components contain the proteins required for flagellar rotation and chemotaxis, which function as a propeller when rotated at its base [30]. [PERSON] _et al._[19] have suggested that _H. pylori_ utilize a proton motive force for flagellar motility. It has also been reported that the velocity of _H. pylori_ cells decreases in response to increasing concentrations of urea, likely due to lack of protons that would be required to neutralize excess ammonia when urea is present in a more neutral (pH 4.5-7) environment [31]. _In vitro_ tests show that _H. pylori_ is acid-sensitive, but is protected from acid (pH < 4.0) by the ammonia released during urea hydrolysis, which is associated with its inherent urease activity [32]. Therefore, _H. pylori_ can survive in the presence of urea when exposed to acid _in vitro_. In keeping with these observations, we found that _H. pylori_ exhibits restricted motility in a near neutral environment. _H. pylori_ is generally thought to have four chemoreceptors: TlpA, TlpB, TlpC, and TlpD Proteins TlpA, TlpB, and TlpC span the inner membrane, which means that part of the protein is located within the periplasm, which is the space between the two membranes of Gram-negative organisms, while another part of the protein is located in the cytoplasm; TlpD is localized completely within the cytoplasm [15]. In _H. pylori_, four different regulatory proteins, CheA, CheY, CheW, and CheZ, are responsible for the transduction of the signal that initiates flagellar motor. When compounds, such as urea bind to the Tlp receptor, allosteric changes in the receptor propagate to a CheY kinase, called CheA. CheA then catalyzes the transfer of a phosphate from adenosine triphosphate (ATP; cellular energy source) to a cytoplasmic protein, CheY; the phosphorylated form of CheY is called CheY-P. CheY-P is able to interact with the motor at the base of the flagellum. The flagellar motor essentially operates as a sensor for CheY-P, whose output is a tendency toward rotation of the flagellum leading to cell tumbling [30]. The interaction of physically proximal receptors may be an important factor in deciding how cells react to even small changes in chemoattractant concentrations. In our study, _H. pylori_ cells were attracted to urea.