Welcome back to another riveting installment of D4!!! Dylan
and I hope that everyone had a great holiday weekend full of family, friends,
and candy, but now to the exciting stuff…
This week in lab
Dylan and I investigated the motility of our still UNKNOWN soil microbe.
Unfortunately, due to time constraints in the laboratory we were unable to
preform the Flagellar Stain, but did get to perform the Soft Agar Deep Test.
The Soft Agar Deep Test uses a
semisolid media in a tube (unlike other solid gel agar media), which allows
motile bacteria to move through. The growth of motile bacteria in this type of
test will produce turbidity (cloudiness) throughout the semisolid agar. This
result can be compared to non-motile bacteria, which will only show growth along
the agar where it was inoculated. Three different tubes were made in order to
compare our unknown microbe against a positive control (E. coli) and a
negative control (Staphylococcus aureus). After the tubes had been
inoculated they were incubated for 24‐72 hours (depending on how slow of a
grower the unknown microbe is). Based on our experiment there are a few
questions that need answering!
1.) Did the microbe appear to be motile?
 |
| Left: B. megaterium, Middle: E. coli, Right: Unknown. |
To the right is a picture of our
unknown microbe next to two controls, a positive control (B. megaterium), and a
negative control (E. coli). Unfortunately there was a complication with the
experiment! For some reason the strain of E. coli we chose to serve as our
negative control was not motile like most other strains of E. coli with
peritrichous flagella…. In order to help with extrapolating our results we are
using both E. coli and S. aureus as negative controls. Our unknown microbe did
not resemble either the positive control or the negative control, and this
could be due to a few reasons; 1.) a poor stab into the Soft Agar Deep tube,
2.) the microbe is unable to tolerate anaerobic growth, or 3.) the microbe is
motile and it “swam” out of the stab and reached the surface of the agar.
 |
| Left: E. Coli, Middle: B. Megaterium, Right: Unknown. |
- We do not think that this result is due to a poor stab, even though the stab of our negative control was not of the highest quality.
- To determine if our microbe is able to tolerate anaerobic growth we reexamined our Triple Sugar Iron. If our TSI slant shows that our microbe was unable to handle anaerobic growth then this would determine that the unknown microbe was incapable of growing in the Soft Agar Deep tube. Upon looking at our TSI slant we determined that our microbe is able to handle anaerobic growth, so this second possibility for seeing no growth is also ruled out.
- Lastly, is the possibility of the microbe “swimming” out of the site of inoculation. We are unsure as to if this is the answer that solves our problem, but it is definitely a possibility!
2.) What cellular structure(s) contribute to
bacterial motility?
 |
| Peritrichous Flagella |
 |
| Bacterial Axial Filament |
Certain bacteria called Spirochaetes are helical, and they have specialized locomotive structures. The specialized structure that a Spirochaete possesses is called an axial filament, and it differs from the flagella because it uses spiral motion that rotates the bacterial cell as it propels it forward.
3.) Why might some microbes have evolved to be
motile?
I would say that bacteria have evolved to be motile for numerous reasons; reproduction, food, and positive environments. Examples of this movement are positive and negative chemotaxis and phototaxis. Chemotaxis is the movement that occurs by an of an organism that is responding to a chemical stimulus. This movement is important for bacteria to find the highest concentration of food molecules in their surrounding environment or swimming away from poisons that have the potential to harm them. Phototaxis on the other hand, is the movement that occurs when an organism moves away (negative) or closer to (positive) a light stimulus. This kind of motion is very beneficial for phototrophic organisms, so they can acquire light to power photosynthesis.
Still slowly discovering our dirt...
As of last week we have conducted six experiments to deduce the identity of our
unknown soil microbe. We have done a Gram stain to determine if our microbe is gram
positive or gram negative, we have tested to see if our microbe was acid or non-acid fast,
we have tested for catalase activity, we have tested to see if our microbe
is aerobic or aerobic, we have performed an endospore stain to determine if our unknown
is endospore forming, and most recently we used a Soft Agar Deep Test to see if our
microbe is motile or not
We have determined so far, that our bacteria is neither gram positive or gram
negative, but rather a bacteria called endospore-forming bacteria, which is a mix of
bacilli and cocci shaped bacteria. We have also determined that our bacteria is non-acid
fast due to the color it appeared after staining. There was also no sign of bubble
formation during the catalase test which means that our bacteria has no catalase activity.
Finally, we tested to see if the bacteria was an aerobic or anaerobic bacteria, and the
results stated that there was activity of both types of metabolism. As for the endospore
stain Dylan and I determined that our unknown microbe is endospore forming, and lastly
our Soft Agar Deep Test has provided results that do not lead us to 100% conclusion of
whether or not our microbe is motile or not.
http://biology.clc.uc.edu/fankhauser/Labs/Microbiology/Prepared_Slides/Bacterial_Anatomy.htm
http://www.slideshare.net/rajud521/bacterial-anatomy
http://en.wikipedia.org/wiki/Phototaxis
http://en.wikipedia.org/wiki/Chemotaxis
I would say that bacteria have evolved to be motile for numerous reasons; reproduction, food, and positive environments. Examples of this movement are positive and negative chemotaxis and phototaxis. Chemotaxis is the movement that occurs by an of an organism that is responding to a chemical stimulus. This movement is important for bacteria to find the highest concentration of food molecules in their surrounding environment or swimming away from poisons that have the potential to harm them. Phototaxis on the other hand, is the movement that occurs when an organism moves away (negative) or closer to (positive) a light stimulus. This kind of motion is very beneficial for phototrophic organisms, so they can acquire light to power photosynthesis.
Still slowly discovering our dirt...
As of last week we have conducted six experiments to deduce the identity of our
unknown soil microbe. We have done a Gram stain to determine if our microbe is gram
positive or gram negative, we have tested to see if our microbe was acid or non-acid fast,
we have tested for catalase activity, we have tested to see if our microbe
is aerobic or aerobic, we have performed an endospore stain to determine if our unknown
is endospore forming, and most recently we used a Soft Agar Deep Test to see if our
microbe is motile or not
We have determined so far, that our bacteria is neither gram positive or gram
negative, but rather a bacteria called endospore-forming bacteria, which is a mix of
bacilli and cocci shaped bacteria. We have also determined that our bacteria is non-acid
fast due to the color it appeared after staining. There was also no sign of bubble
formation during the catalase test which means that our bacteria has no catalase activity.
Finally, we tested to see if the bacteria was an aerobic or anaerobic bacteria, and the
results stated that there was activity of both types of metabolism. As for the endospore
stain Dylan and I determined that our unknown microbe is endospore forming, and lastly
our Soft Agar Deep Test has provided results that do not lead us to 100% conclusion of
whether or not our microbe is motile or not.
http://biology.clc.uc.edu/fankhauser/Labs/Microbiology/Prepared_Slides/Bacterial_Anatomy.htm
http://www.slideshare.net/rajud521/bacterial-anatomy
http://en.wikipedia.org/wiki/Phototaxis
http://en.wikipedia.org/wiki/Chemotaxis
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