Nitrobacter is a genus of rod-shaped, gram-negative bacteria found widely in natural environments like soil and aquatic systems. These microorganisms are classified as chemoautotrophs, producing their own food by obtaining energy from chemical reactions rather than from sunlight. Nitrobacter derives its energy by oxidizing inorganic compounds, playing a role in the transformation of nitrogen. This metabolic ability allows these bacteria to thrive in various ecosystems.
The Process of Nitrification
Nitrobacter performs a specialized step within nitrification, a natural biological conversion of nitrogen compounds. This bacterium is responsible for the second stage of nitrification, oxidizing nitrite (NO2-) into nitrate (NO3-). The reaction is represented by the chemical equation: 2NO2- + O2 → 2NO3-.
This conversion follows the initial step of nitrification, performed by other bacteria such as Nitrosomonas. Nitrosomonas converts ammonia (NH3) or ammonium (NH4+) into nitrite, creating the substrate Nitrobacter then utilizes. The enzyme nitrite oxidoreductase (NXR) facilitates the oxidation of nitrite to nitrate within Nitrobacter cells. This sequential action ensures a continuous transformation of nitrogen, making it a less toxic and more usable form for plants and other organisms.
Environmental and Commercial Applications
Nitrobacter plays a role in several practical applications. In aquariums, these bacteria are important for the “cycling” process of a new tank. They convert harmful nitrite, which originates from fish waste and decaying organic matter, into less toxic nitrate, making the aquatic environment safer for fish. These beneficial bacteria readily colonize surfaces such as filter media and gravel, where they can effectively process waste products.
In agriculture, Nitrobacter contributes to soil fertility by transforming nitrites into nitrates. Nitrates are the primary form of nitrogen that plants can readily absorb through their roots for growth and development. This conversion ensures that nitrogen is available in a usable form, thereby supporting healthy crop yields.
Nitrobacter is also utilized in wastewater treatment facilities to remove nitrogenous compounds from sewage. By oxidizing nitrite to nitrate, these bacteria reduce the concentration of harmful nitrogen forms in treated water before it is discharged. This biological removal process prevents water pollution and minimizes the risk of eutrophication in receiving water bodies.
Factors Affecting Nitrobacter Activity
The activity of Nitrobacter is influenced by several environmental factors. Temperature is important, with Nitrobacter showing optimal growth and activity between 25 and 30°C (77-86°F). Activity can be significantly reduced at temperatures below 4°C (39°F) and may cease or lead to bacterial die-off above 49°C (120°F).
The pH level of the environment also impacts Nitrobacter, with an optimal range generally between 7.3 and 8.0. Conditions that are too acidic, such as a pH below 6.0, can inhibit their nitrification activity, leading to the accumulation of harmful nitrites. Highly alkaline conditions, above pH 9.0-9.5, can also impair their function.
Nitrobacter is an obligate aerobe, requiring oxygen to perform its metabolic processes. Sufficient dissolved oxygen levels are necessary for the efficient oxidation of nitrite to nitrate. Low oxygen concentrations can reduce the bacteria’s metabolic rate and overall effectiveness. Certain substances can also inhibit Nitrobacter activity, including high concentrations of toxic ammonia. Some pesticides, such as CIPC, chlordane, heptachlor, and lindane, can prevent or partially inhibit Nitrobacter growth and nitrite oxidation.