The Motility Possibility

In further research to determine the elusive identity of our soil microorganism, we performed a soft agar deep test to evaluate motility. This test helps discern whether to categorize a bacteria as motile or non-motile. If a bacteria is motile, it will have the capability to move through the agar due to the nature of the semi-solid media. The positive control, E. coli, exhibits bacteria motility by expanding away from the stab inoculation line, while the negative control, S. aureus, grows solely along the inoculation line.  

E. coli 

S. aureus

Incidentally, the results of the soft agar test did not reveal a conclusive answer about the motility of our microbe. As displayed in the picture below, there is no clear growth along, or radiating from, the stab inoculation line. Though the agar appears slightly cloudy, the only definitive microbial growth occurs on the surface of the soft agar.

Unknown Microorganism

Despite not having an obvious answer regarding the motility of our unknown, we are still capable of postulating characteristics that could ultimately lead to it's identity. Last week, we determined that our unknown bacteria could be either aerobic or anaerobic. If the bacteria is aerobic, then it could not tolerate anaerobic growth. There is also the possibility that our unknown is motile and migrated to the surface of the media, instead of remaining the in the stab line.

Motile capability results from the presence of flagella on prokaryotic organisms. The momentum arises from the counterclockwise rotation of individual flagella bundled together. Bacterium often move in certain direction as a result of environmental cues, a process known as chemotaxis. They will either migrate toward or away from compounds due to the detection of concentration gradients. This process has evolved form the survival of bacterium with better receptors and flagella, and their movement to and from certain chemicals. The only downside to flagellar motility is the inability to move within small spaces. Because a microbe needs to rotate in order for flagella to create momentum, tightly compact areas prevent proper movement, inhibiting motility. 

Though motility is a helpful identifier, it does not help us narrow down our possible bacteria options using the dichotomous key. More testing, specifically on nitrate reduction, is required. Last week we stated our unknown bacterium could possibly be Lactobacillus spp., while eliminating Clostridium spp. due to the lack of endospore production. As of this week, Lactobacillus spp. and Acitonomyces spp. are contending for the identity of our unknown microorganism.

Berg JM, Tymoczko JL, Stryer L. Biochemistry. 5th edition. New York: W H Freeman; 2002. Section 34.4, A Rotary Motor Drives Bacterial Motion. 

http://www.ncbi.nlm.nih.gov/books/NBK22489/

-Palmer Miller