Nitrifying bacteria, autotrophic

Nitrification seems limited to a number of autotrophic bacteria. The dominant genus that is capable of oxidizing ammonia to nitrite in soils is Nitmsomonas, and the dominant genus capable of oxidizing nitrite to nitrate is Nitrobacter. Normally, the two processes are closely connected and nitrite accumulation does not occur. Nitrifying bacteria are chemolithotrophs that utilize the energy derived from nitrification to assimilate C02. 

Autotrophic nitrifying bacteria (e.g., Nitromonas europea) can use nitrite to oxidize ammonia with the production of nitrogen gas (when oxygen is absent). 

HAO catalyzes the four-electron oxidation of hydroxylamine to nitrite. " It is present in autotrophic nitrifying bacteria, like Nitrosomonas, which are obligate chemolithotrophs that use the oxidation of ammonia as their sole energy source. For each cycle of hydroxylamine oxidation, two electrons are returned for the initial step of ammonia oxidation and the other two are either transferred to the terminal oxidase via the components of the respiratory chain, or used to generate NADH by reverse electron transport. 

The nitrifying bacteria, universally found in aerobic soil and aquatic environments, derive energy from the oxidation of reduced inorganic nitrogen compounds (ammonia and nitrite). As do autotrophic bacteria, they obtain carbon from carbon dioxide in the atmosphere. 

The autotrophic nitrifying bacteria are more sensitive to unfavorable conditions in the soil than are most other common soil microorganisms. This raises the question as to the extent to which they may be killed by additions of our common fertilizers. Such materials, if high in soluble salts or if they are highly reactive substances, can kill some or most of the organisms in a restricted area where the fertilizer is highly concentrated. Anhydrous ammonia is probably the worst offender. The organisms that are an inch or more away from these chemicals are unaffected and as the chemical is sorbed, diluted, or transformed, they quickly spread into the affected area. The result is that none of the fertilizer materials in common use, and supplied at normal rates, are likely to have much direct harmful effect on the soil as a whole for more than a few days. The main exception to this statement is the effect on pH, discussed below. 

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