Kelly Young

Unknown Specimen 5

Bacillus megaterium

Kelly12/5/2012

Unknown Specimen 5

In microbiology lab class, my partner Virginia Dutra and I obtained unknown bacterial

specimen 5. We performed a gram stain to determine that the sample consists of gram positive

rod shaped bacteria growing in short chains. According to this initial information, we determined

that the bacteria were spore forming, and likely a Bacillus species.

The Fluid Thioglycolate Medium (FTM) test we ran on specimen 5 indicated that our

bacteria is facultative anaerobe, as growth was present throughout the tube, yet more

concentrated at the top of the tube, where more oxygen is present. The test ran using the

Simmon’s citrate resulted negative. Of our fermentation testing results, our specimen was

positive for the following: Glucose acid/gas, Lactose gas, Sucrose acid/gas. This further

convinced us that we had a facultative anaerobic specimen. Our hydrolysis positive results were

as follows: gelatin, and casein. Our specimen tested positive for Methyl red and V-P. When the

specimen was tested for nitrate reduction, a positive result was found. The catalase test resulted

in a positive result. With this information, I began to look at flow charts for a general idea of

what bacteria unknown specimen 5 may be.

Of the options, I narrowed it down to possibly being Bacillus cereus, Bacillus coagulans,

or Bacillus megaterium. Initially, the test results I found for B. coagulans seemed to match the

results I found for specimen 5. This was the case for B. cereus as well. B. megaterium results that

I read did not seem to match up as well, since the general results for this bacteria stated that the

VP test is negative, and that the fermentation results were different. According to most results I

found, the starch and citrate tests were positive for B. megaterium, and the results we found were

negative. Concern aroused when it was discovered that there was conflicting reports on

respiration. I discovered, depending where one looks, B. megaterium is an obligate aerobe,

facultative anaerobe, or aerotolerant. Considering flow charts, Bergey’s Manual, and the general

information I found, I believed the specimen to either be B. cereus, and B. megaterium would be

off the list. This did not seem to be the end, as the morphology of B. cereus did not match up

with our specimen quite as well as the colonies of B. megaterium I studied, and the fact that B.

cereus is an aerobe. Our unknown specimen contained large, heaped, shiny white raised colonies

that with age grew filamentous edges. After observing the colony morphology of a known plate

of B. megaterium, I was absolutely sure that unknown specimen 5 is Bacillus megaterium.

Bacillus megaterium is a gram positive rod that grows in short chains. Its colony

morphology is large, shiny and white, with filamentous edges. Of the tests we ran on our

specimen, all matched up with the following exceptions: the citrate, urease, and nitrate reduction

results, and respiration. I read that 90% of the bacteria will follow suit on what is typically

reported in results, I believe that our specimen falls under the rule for exception, as seen in the

results I have reported, including the fact that our specimen is a facultative anaerobe. B.

megaterium is non-pathogenic bacteria typically found residing in soil. Its genome has been fully

mapped, and it is commonly used in laboratory applications. The species is named megaterium

due to its large size, megatherium in Greek means “great beast”.