Catalase, Slants, and Butts: A look into our soil microbe's catalase activity and carbohydrate metabolism

In lab, the week before Spring Break, Austin and I further analyzed our soil microbe using the catalase activity test and triple sugar iron test. The overall premise of the catalase activity test is to determine if the microbe is catalase positive or negative. Catalase is an antioxidant enzyme that protects cells from oxidative stress. In this case, if catalase is present, then it will neutralize the hydrogen peroxide into water and oxygen gas. This neutralization of catalase-positive samples causes bubbling after adding a drop of hydrogen peroxide, and catalase-negative remains unchanged. Some microbes have evolved to acquire catalase activity. This could be primarily due to the added protection from oxidative stress that catalase-positive microbes possess.

To determine the catalase activity of our soil microbe, we first observed the reactions of a catalase-positive and catalase-negative control. When we added hydrogen peroxide to our soil microbe, the sample bubbled indicating it was catalase-positive.

The other test we conducted was the triple sugar iron test, which is used to determine the type of carbohydrate metabolism that the microbe utilizes. This specific experiment differentiates between lactose, glucose, and sucrose fermentation and hydrogen sulfide production. We inoculated our soil microbe and 4 controls on slants containing the triple sugar iron agar. After returning to the lab after 2 days of incubation, the controls behaved as we anticipated. The controls were characterized based on the color of the slant and butt. Our soil microbe was yellow at the slant and butt. This color is characteristic of an acid over acid tube, which we also saw with the E. coli control. Metabolically, our soil microbe fermented lactose and/or sucrose. Our soil microbe and the controls can be seen in the picture below.

(FROM LEFT TO RIGHT) Our soil microbe, B. megaterium, E. coli, P. areugrinosa, P. vulgaris

The fact that our soil microbe is catalase-positive and a lactose and/or sucrose fermenter does not change any of the previous classifications of our microbe.  It is still narrowed down to either genus Myobacterium or Nocardia.

Check back next week for more information from Austin about our soil microbe's endospore stain!

-Anne

http://onlinelibrary.wiley.com/doi/10.1002/0471140856.tx0707s27/abstract