2. TAXONOMIC DESCRIPTION
Nitrosomonas species belong to the family Nitrobacteraceae which contains two groups responsible for nitrification. The first group oxidizes ammonia to nitrite (Nitrosomonas belongs to this group), the second group oxidizes nitrite to nitrate. Nitrosomonas species grow chemolithotrophically using reduced inorganic nitrogen compounds as a source of energy. Some species of Nitrosomonas utilize urea by way of urease as an ammonia source. Metabolism is aerobic, NH4+ is the electron donor and O2 is the electron acceptor. Most species are motile with flagella located in their polar regions but some species are nonmotile.
DNA homology experiments are used to determine the presence of further species. Distinguishing characteristics for the species that are used in identification are the G+C content of DNA, the shape and size of cells, salt requirement, urea utilization, the presence of carboxysomes, and cell protein patterns.
Isolation requires a selective media with ammonia as an electron donor and bicarbonate as the sole carbon source. Media requirements include an extensively washed high purity agar or a silica gel agar. The media has to be completely inorganic because growth is inhibited by the presence of organic materials. Also, growth is slow which enable overgrowth of contaminants. Isolation is extremely difficult and colonies formed are very small in diameter. Visible turbidity may not be seen even after extensive nitrification so the best means for growth detection is to assay for the production of nitrite. One to two weeks is needed for incubation, then the chemical assays will reveal successful enrichment and an attempt to isolate pure cultures can be made.
|Nitrosomonas species are found widely distributed in soil and water. They are present where considerable amounts of ammonia are available. Species grow well in lakes and streams that receive inputs of untreated and treated sewage. They also strive more in neutral and alkaline habitats because acidic environments inhibit nitrification. Ammonia tends to accumulate in anaerobic habitats since oxygen is required for ammonia oxidation, but nitrifying bacteria tend to develop at the thermocline in stratified lakes where ammonia and oxygen are both present.|
The above picture shows Nitrosomonas europea under electron microscopy (39,600X).
4. ADDITIONAL SOURCES OF INFORMATION
Atlas, R.M. 1995. Principles of Microbiology. Mosby. St.Louis, MO. 900 pp.
Brock,T.D., M.T. Madigan, J.M. Martinko and J. Parker. 1994. Biology of Microorganisms. Prentice Hall. New Jersey. 908 pp.
Gerhardt, P., R.G. Murray, R.N. Costilow, E.W. Nester, W.A. Wood, N.R. Krieg and G.B. Phillips.eds. 1981. Manual of Methods for General Bacteriology. American Society of Microbiology Press. Washington D.C. p. 125.
Holt, J.G., N.R. Krieg, P.H.A. Sneath, J.T. Staley, and S.T. Williams. 1994. Bergey's Manual of Determinative Bacteriology. Ninth Edition. Williams and Wilkins. Baltimore, Maryland. 787 pp.
Microbial Ecology of the Nitrogen Cycle - A chapter from a Microbial Ecology course at University of Waterloo in Canada.
Behavior and Physiology of Nitrifying Bacteria - publication by James E. Alleman, Ph.D. and Kurt Preston from the Scool of Civil Engineering at Purdue University.
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