In this screencast video lecture, we are going to see about the nitrifying bacteria. This is also an important hemolytotrophic bacteria. As the name implies, this bacteria use reduced inorganic nitrogen compound, such as ammonia and nitrate as their sources of energy for growth and metabolism. Here, ammonia is oxidized to nitrate by one group of nitrifiers, which is referred as the ammonia oxidizing bacteria or ammonia oxidizes. Their overall reaction has been shown there. Ammonia in the presence of oxygen, it is oxidized there into nitrate. During this process, you will be getting energy that would be used for 80-pcentresses. The next process is the nitrate that have been formed by ammonia oxidizes is further oxidized to nitrate by another group of organisms called as nitrite oxidizes. The overall reaction is nitrate is converted to nitrate with the release of energy that energy will be used for again 80-pcentresses by the organism. You look at the next point there. No single nitrifying bacteria was able to oxidize ammonia all the way to nitrate. This is a very old point. That is the reason I have striked that point. Recently, they have identified a group of organisms called as a comma-mox, that is, complete ammonia oxidizing bacteria. This bacteria basically belonging to the phylum nitrospyra, they are all capable of completely oxidizing ammonia to nitrate. In the diagram, you can able to see a complete oxidation of ammonia to nitrate that have been shown there in the red color. Normally, the two groups of nitrifying bacteria, that is, ammonia oxidizes, as well as nitrite oxidizes, grow in close association the environment. Since the two sequential oxidation steps need to be coupled together, that is, both the process need to happen simultaneously. Since the nitrate that have been formed in the first steps are always toxic for the higher organism, if it gets accumulated there in the environment. Nitrifying bacteria are found in all soil and aquatic habitats, and are especially common in alkaline and neutral ph-environments. This organism grow well in pure culture, and completely inorganic media. Most species are also able to utilize organic carbon sources such as acetate for their growth, which intend to mean that they are facultative hemodotrophic in nature. They have a generation times of 24 hours or more, the reason for their poor growth in the pure culture may be attributed to reasons such as toxicity of nitrate on the growth and metabolism of these organisms. Now we look at the points later to the first group of organisms, that is, ammonia oxidizes. They are capable of oxidizing ammonia to nitrous acid, which involves two major steps with hydroxide lamination, intermediate in the process. The two steps have been catalyzed as shown in the reaction. First steps involve the enzyme, ammonia monooxygenase for its activity, whereas the second step essentially required hydroxylamine oxidoreductase enzyme to carry out the process. On collective operation of these two reactions, they are able to get enough amount of energy that is required for synthesizing their ATP. The important group of nitrifying bacteria has been listed here. The first group comprises of ammonia oxidizes. Important organisms here are nitroso monos, nitroso-spyra, nitrosolobus, and the second group is nitrite oxidizes. The important organism here is a nitrobacter. And finally, you can able to see one genera named nitrospyra. It specifically belongs to a phyla called as a nitrospyra, which is a separate phyla, which mainly contain the pomeomox group of organisms, which I have earlier discussed, that is, that can be able to perform the whole process in a single step, that is, from ammonia to nitrate. Instead of two different groups, that is, ammonia oxidizes and nitrite oxidizes are involved in their process. The next one is a nitrite oxidizes. The nitrite oxidation is a single step oxidation process. It is carried out by the enzyme nitrite oxidoreductase. The overall reaction of the wind showed that, in which significant amount of energy is generated, that could be useful for ATP synthesis. This nitrifying bacteria have a complex internal membrane system that contains cytochromes, and this intra-cytoplastic membranes are thought to contain the cytochromes system that acts as a site for ammonia or nitrate oxidation, as well as they are the site-sigvolved in the generation of the reducing ecolumns like NVDH. Finally, we look at into the ecological significance of this nitrifying group of organisms. Although they occur as low population there in the various habitats, they are very active metabolically there in the environment. Nitrite does not accumulate in most environment, mainly due to the tight coupling between the ammonia oxidation, as well as nitrite oxidation process. Therefore, nitrite, which is a toxic or butogenic molecule for the plants or animal will be typically occurring at a very low concentration in the environment, which is mainly due to the rapid oxidation of the nitrite to nitrate molecule. The activities of nitrifying bacteria are especially important soil environment, as they play an important role there in the nitrogen cycling. Among the various nitrogen sources, ammonium form of nitrogen is a preferred source of nitrogen for the crop fertilizer. The principle reason being that is, ammonium are more readily retained in the soil because it is positively changed. Nitrate on the other hand is highly soluble and they may readily leach it out from the soils. There is also a chance in which the nitrate formed by the action of the nitrifiers can be further converted into atmospheric nitrogen by the B-nitrifying group of organism. As a result, the nitrogen may completely loss from the soils. For this reason only, certain commercially available fertilizers like nitropyrene have been developed, which can be able to influence control over the nitrification process, thereby they can minimize the nitrogen loss from soil. One more environment in which the ammonia will be dominating is the seawage, as it contains a lot of proteins and amino acids, which undergoes degradation or decompotion that results in the accumulation of ammonia. As a result, ammonia will be discharged in the huge quantities in the seawage outfalls. This in turn increases the biochemical oxygen demand since the process of nitrification requires oxygen. Due to this reason only, the modern wastewater treatment plants are designed to encourage the growth of nitrifying bacteria within the treatment plant. So the downstream water may not contain more amount of nitrogen compound, which may cause eutrophication problems when such a seawage water has been discharged into water bodies like ponds.