MIDTERM 2 MOTILITY Flashcards
What is motility defined as?
Self-directed movement of a cell from one position to another without involvement of physical forces such as agitation of the medium
What form of motility is the most common and well understood?
Flagellar motility is most common and the mechanisms of movement are well understood
What is Flagellar motility?
Whip-like structures anchored in the cell membrane and can rotate CW or CCW to produce tumbling or running movements of the cell.
What are positive chemotaxis?
Movement towards a favorable chemical environment
What are Negative Chemotaxis?
Movement towards an unfavorable environment
Positive and Negative phototaxis?
in response to light
Positive and Negative Geotaxis?
In response to gravity
Positive and Negative Magnetotaxis?
in response to earths magnetic fields
Why are flagella so hard to see? whats their size?
theyre well below the limit of resolution of a light microscope with a diameter of 0.01 to 0.05 uM
What happens in the Leifson Flagellar Stain?
Tannic acid precipitates along the flagellar surface and serves to hold the basic fuschin stain. The accumulation of stain on the flagellum amplifies the size and increases its visibility under the light microscope
What shapes are most flagellated bacteria?
They are rods with few examples of cocci
What is Monotrichous?
Single Flagella inserted at the ends of a cell (polar flagella)
What is polytrichous
Numerous flagella inserted at the ends of the cell or distributed over the entire surface (peritrichous)
Does having flagella ensure motility? if no, Why?
No it does not.
- Cultures in stationary phase of growth may consist of dead cells or cells that are unable to efficiently utilize nutrients in the environment to produce energy required for motility
- Cells that are young and flagellated may lose their flagella in the process of making a wet mount and show little to no motility under microscope
What can affect motility?
- Presence/Absence of some nutrients
- Changes in the growth Temperature
- Degree of Aeration
Basic requirements for detecting motility?
- Cells must be inherently capable of producing flagella
- Cells must be growing in conditions appropriate for motility
- Cultures should be young and capable of growth and physiological activity
- the culture must be handled gently
What form of microscopy is best to observe motility?
Phase Contrast
How can motility be determined indirectly?
By observing that organisms that were inoculated in one place have moved and grown in a region of the medium that was not inoculated.
Explain Swarming motility
Bacteria capable of high levels of motility may spread rapidly across the surface of an agar plate ( SPREADING)
Why does swarming occur?
Nutrients are exhausted in the region of inoculation, stimulating organisms to spread out in direction of higher nutrient concentration
Problem with swarming colonies?
Swarming introduces complications in attempts to produce isolated colonies on a plate as the swarmer may rapidly overgrow other non swarming colonies
What medium is used to test Motility ?
Soft Agar Deeps
What is the property of a soft agar deep?
its more of a viscous medium than a solid agar
How does viscosity affect motility?
only the stronger , higher level motile microbes can move through it
Positive test for motile organisms in the soft agar deep?
Growth present away from the stab
Soft Agar Deep can be used to test for motility, but what makes it so special that it can test for something else?
The soft agar can close up along the stab so that the path of the stab is no longer visible and cannot serve as a path for entry of oxygen from the airspace in the deep.
- If bacterium is an obligate aerobe, growth will stop after the oxygen runs out in the deep.
- Only organisms that are facultative will continue to grown in absence of oxygen.
When can the Soft agar Deep only be used as a motility test?
if the organism is a facultative anaerobe and it will only exhibit motility if its actively motile as well
