Bacterial Identification

[Jirara]

I worked through all the tests for ID on a microorganism I got from the soil, but I can't figure out what it actually is.

[Jirara]

Here are the details:
Sucrose -
Dextrose -
Lactose -
Potato Dextrose -
Spirit Blue (lipid) +
Skim Milk -
Oxidase +
Catalase +
Nitrate Reduction + (didn't form gas, but there was no nitrate or nitrite).
Colonies are light whitish on the outside, opaque white in the center, convex, glossy, and meld into each other if they touch.

[donnahardy2]

Hi Jirara,

This is a very interesting project.

Do you have access to a laboratory where you can do a Gram stain and look at this organism under a microscope? Bacillus species, which are very common soil organisms, are catalase and lipase postive, nitrate negative and vary in their ability to ferment sugars. If this were a rod-shaped bacterium, it would hep confirm the identification. You could also check for spore production on an older culture of the organism.

Donna Hardy

[Jirara]

Yeah, I looked at them under a microscope yesterday. It looks like their Gram + rods. I forgot to fix them the first time, and they were swimming all over, so they are motile. They also do not form spores, as far as I can tell. I think they do reduce Nitrate, just not to N2 or Nitrite.

[donnahardy2]

Hi,

Do you have a really old culture to check for endospores again? If possible, do a spore stain on the oldest colony you have available. The presence of spores will really help confirm the identification of this as a Bacillus species. If this is not a spore-former, then there’s a different path to go down for the identification. Here’s a key for identification of Bacillus species. Can you do a starch hydrolysis, VP, and a citrate test? Was there a micrometer on the microscope to you can estimate the cell diameter.

http://www.uiweb.uidaho.edu/micro_biolo ... charts.pdf


Donna Hardy

[Jirara]

I'll see if I can do another spore stain (I didn't see spores the first time, but the colonies were only 2 weeks old, I think). Catalse +, and does NOT hydrolyse starch. Thank you for posting the identification key - it is very helpful.

[donnahardy2]

Hi,

Let me know if you get any more test results. What does this bacterium look like in a broth culture? Normally, since Bacillus species are aerobic, they will form a pellicle on the surface of a liquid culture.

Is the identification of this organism part of your science fair project?


Donna Hardy