Nitrite-oxidizing bacteria (NOB) are a group of microorganisms that play a crucial role in the nitrogen cycle. They convert nitrite (NO2-) into nitrate (NO3-), which is a more stable form of nitrogen that can be utilized by plants. This process helps maintain the balance of nitrogen in ecosystems and is essential for soil health. NOB are commonly found in various environments, including soil, freshwater, and marine ecosystems. They thrive in aerobic conditions, meaning they require oxygen to survive. By facilitating the conversion of nitrite to nitrate, these bacteria contribute to nutrient cycling and help prevent the accumulation of toxic nitrite levels in the environment.