Bacterial Motility and the Hanging Drop Slide PDF

w V') u a: w >< w BACTERIAL MOTILITY AND THE HANGING DROP SLIDE LEARNING OBJECTIVES----------- 1. Describe the three types of movemen...

w V') u a: w >< w BACTERIAL MOTILITY AND THE HANGING DROP SLIDE LEARNING OBJECTIVES----------- 1. Describe the three types of movement found in bacteria and identify the str that allow for movement. uctures 2. Identify the components of a bacterial flagellum and where each is found. 3. Describe chemotaxis and how flagella contribute to this process. 4. Compare and contrast runs and tumbles. s. Draw the four flagellar arrangements that may be found in bacterial cells. 6. Using a bright light microscope, view and identify the arrangement of bacterial fla- gella. INTRODUCTION--------------- Approximately half of all known bacterial species are capable of movement. In Brownian movement, random motion of water molecules h1tt1ng bacterial cells causes them to move. Most bacteria (even the nonmotile species) display this movement when placed in an aqueous environment and this is not considered to be true motility. Motile bacteria, on the other hand, move with speed and apparent purpose in their environments and are capable of movement by several different mechanisms. Certain bacteria move over surfaces with a gliding motility. Such bacteria can only display movement when they are in contact with a solid surface. Organisms known as spirochetes display corkscrew or bending-type motility due to the presence of axial filaments. These filaments are composed of axial fibers which are modified flagella that wrap around the bacterial cell. The most common type of movement dis- played by bacteria, however, is due to the presence of flagella. Flagella are long, helical, semirigid appendages that move the cell by rotating either clock- wise or counterclockwise from the point of attachment with the cell. Prokaryotic flagella are composed of three parts-a basal body, a hook, and a filament. The filament is the portion of the flagella that extends outward from the microorganism and rotates to propel the organ- ism through its environment. It is composed of multiple units of flagellin protein which are arranged in a helical arrangement around the core of the flagellum. The flagellum inserts into a hook, which is composed of a different type of protein, at the surface of the bacterial Cell. The protein, basal body, consists composed of a rod of a third and a series of of rings. The number and location of these rings moV  differ depending on whether the Figure 22.1. Examples of bacterial flagellar organism is a arrangements. gram-positive or gram-negative. All flagella are capable of rotating 360 degrees. The ability to move either towards or away from a chemical stimulus is a beneficial trait and is known as chemotaxis. Organisms can sense the presence of chemicals and will move towards an attractant such as a desirable nutrient. On the other hand, motile organisms will actively move away from a toxic substance. When flagella rotate in a counterclockwise fashion, the organism is propelled forward in movement known as a run. This movement typically only lasts a short time. The rotation of the flagella then reverse to clockwise, which causes the organism to stop abruptly and roll about, an action known as a tumble. When the organism senses it is moving towards an attractant, the runs become longer and the tumbles become less frequent. Conversely, tumbles are more frequent, while runs are of shorter duration when an organism senses a repellent. A bacterium may possess one flagellum or may have multiple flagella. A monotrichous bacterium possesses a single polar flagellum, while an amphitrichous bacterium possesses a Peritrichous Lophotrichous single flagellum at each end of the cell. Lophotrichous bacteria possess two or more flagella at one or both poles of the bacterial cell. Finally, peritrichous Monotrichous Amphitrichous bacteria possess flagella distributed over the entire surface of the cell. See figure 22.1 for depictions of these arrangements.. Both bacterial motility and flagella can be observed microscopically. A hanging drop slide is useful for observing bacterial motility as well as for observing live microorganisms in general. A drop of liquid bacterial culture is placed within the depression of a depression slide. This type of slide is generally viewed using dark-field microscopy. Because flagella are extremely thin, the diameter of the flagella must be increased in order to visualize flagella under the microscope. These preparations are then stained with a stain such as basic fuchsin or silver nitrate. Flagella stains are notoriously difficult to prepare, so this stain will not be performed on the environmental isolates. TODAY'S PROCEDURE------------- 1 · Yourgraduate teaching assistant has set up a microscope focused on various flagel- lar arrangements of bacteria.It is each student'sresponsibility to view this slide. 2 · Be sure to note any differencesin flagellar arrangements between the bacterial cells. 3. Record all results.