The AOB are grown in a standardized mineral salts solution that they can easily survive In, and ammonium Is added to serve as their food source. The cultures were grown In 48 well plates. The outmost row of each plate contained sterile water, and the Internal plates all had 4 replicates of the following: a negative control, a positive control, 25μM Ni, 50 μM Ni, 75μM Ni, and 100μM Ni. The plates are then placed In an Incubator that maintains a constand temperature. 

AOB are very slow growing for bacteria, so instead of measuring how cloudy the cultures get, they are Instead measured through their byproduct: nitrite. Nitrite itself Is colorless, so a Sulfanil amide reagent Is used to form a Pink Azo dye; the absorbance of this can be read and used to determine growth.