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 an essential process for maintaining soil and water quality. NOB are typically found in various environments, including soil, freshwater, and marine ecosystems. These bacteria are vital for wastewater treatment, as they help reduce harmful nitrite levels, preventing toxicity in aquatic life. Common genera of nitrite-oxidizing bacteria include Nitrobacter and Nitrospira. Their activity supports the growth of plants and contributes to the overall health of ecosystems.