Nitrospira represents a widespread genus of bacteria that plays a role in various ecosystems across the globe. First identified in 1986 from the Gulf of Maine, this bacterium belongs to the phylum Nitrospirota. Members of this genus are typically Gram-negative and exhibit a helical to vibroid shape. These microorganisms are commonly found as clumps within biofilms rather than as free-floating planktonic cells.
The Role of Nitrospira in Nitrification
Nitrospira is widely recognized as a nitrite-oxidizing bacterium (NOB), performing a specific step within the global nitrogen cycle. Its primary function involves converting nitrite (NO2-), a compound that can be harmful in high concentrations, into nitrate (NO3-). This transformation is part of nitrification, a two-step biological process that makes nitrogen available in a form usable by many plants and other organisms. The enzyme nitrite oxidoreductase (NXR) is central to this conversion, facilitating the oxidation of nitrite to nitrate.
These bacteria are generally classified as chemolithoautotrophs, meaning they obtain their energy from the oxidation of inorganic compounds, specifically nitrite, and fix carbon dioxide as their carbon source. Some recently discovered Nitrospira species are capable of “complete ammonia oxidation,” or “comammox.” These comammox Nitrospira possess the genetic machinery to carry out both the oxidation of ammonia to nitrite and the subsequent oxidation of nitrite to nitrate, performing the entire nitrification process themselves.
Where Nitrospira Thrives
Nitrospira is found in a wide array of natural and human-made environments, demonstrating its widespread adaptability. These bacteria are commonly present in terrestrial systems, including agricultural fields and forest soils, where they contribute to soil nitrogen dynamics. They also inhabit various aquatic ecosystems, such as freshwater lakes and rivers, as well as marine environments like oceans, estuaries, and deep-sea sediments.
Beyond natural settings, Nitrospira frequently establishes itself in engineered systems designed to manage water quality. This includes drinking water distribution systems, where their activity influences water chemistry. They are particularly common in wastewater treatment plants and within the biofilters of aquaculture systems, where specific conditions favor their metabolic processes. Their ability to form aggregates and biofilms allows them to colonize surfaces within these systems, which supports their growth and function.
Ecological and Practical Importance
The activity of Nitrospira holds considerable significance for both natural ecosystems and human-managed systems. In the global nitrogen cycle, Nitrospira plays a role in removing nitrite, which can be toxic to many organisms if it accumulates in aquatic and terrestrial environments. By converting nitrite into nitrate, Nitrospira makes nitrogen available in a form that plants can readily absorb, thereby supporting plant growth and overall ecosystem productivity.
In engineered systems, Nitrospira is particularly useful in wastewater treatment plants, where it contributes to nutrient removal and pollution control. Its role in converting nitrite to nitrate helps meet discharge standards by reducing nitrogen compounds before treated water is released. The discovery of comammox Nitrospira offers new possibilities for wastewater treatment, potentially leading to more efficient processes that reduce the emission of greenhouse gases like nitrous oxide. Furthermore, in aquaculture systems, Nitrospira helps maintain water quality by continuously removing toxic nitrite from fish tanks, ensuring a healthier environment for aquatic life.