Ammonia-oxidizing bacteria (AOB) are a group of microorganisms that play a crucial role in the nitrogen cycle. They convert ammonia, a toxic compound, into nitrite through a process called nitrification. This transformation is essential for maintaining soil and water quality, as it helps prevent the accumulation of harmful ammonia levels. AOB are commonly found in various environments, including soil, freshwater, and marine ecosystems. They thrive in conditions with sufficient oxygen and are vital for supporting plant growth by making nitrogen more accessible. Their activity also contributes to the overall health of ecosystems by promoting nutrient cycling.