The Nitrogen Cycle

Table 1. Observations from week 2 for the detection of ammonia using the Nessler’s reagent and from week 1 for the pH using bromothymol blue indicator with the inoculation of P. vulgaris, P. fluorescens, and B. Cereus in peptone broth. Tubes were incubated at room temperature for 7 days and 14 days.

Soil Microorganism

Nessler’s Reagent (color reaction pH (bromothymol blue)
Our results pH (bromothymol blue)
Class results
P. vulgaris Deep yellow
++ 8.0 8.0, 7.5, 6-7, 11.5
P. fluorescens Brown precipitate
+++ 12.0 12.0,12.5
B. Cereus Deep yellow
++ 6.7 6.7, 6.5, 6.8, 7.5
Control*
Light, faint yellow
+ 7.5 7.5, 7.5
*Note: The control used in this test was peptone broth (not inoculated with any culture)

Nessler’s reagent was added to three different soil organisms after their incubation time. As shown in Table 1, P. fluorescens had a brown precipitate which indicates a large amount of ammonia was present. Both P. vulgaris and B. Cereus had a color reaction of deep yellow which indicates that more ammonia was present.
The control had a small amount of ammonia observed by the faint yellow color. The pH values of our group and class values are shown in table 1. The control had a neutral pH with a value of 7.5 hence, a good control. P. fluorescens had the highest pH value of a basic 12.0 and largest presence of ammonia, hence demonstrates that the bacteria are able to produce ammonia. Ammonia has a basic pH value.

Table 2. Observations for 7 days and 14 days for the production of ammonia using Nessler’s reagent, nitrites using Trommsdorf’s reagent, and nitrate using diphenylamine reagent. Soil inoculations of ammonium sulphate and nitrite broths were incubated at room temperature for 7 days and 14 days.
Incubation Period Broth Type Nessler’s
Reagent Trommsdorf’s Reagent Diphenylamine Reagent

7 Days Ammonium Sulfate Broth Colorless- ammonia not present Presence of blue-black color. Nitrite production.
N/A*