Nitrogen cycle organisms

Nitrogen Synthesis of proteins, nucleic acids, etc. Steps in the nitrogen cycle (organic N — NHj —no —NOJ —... 

Figure 14.12 The biological nitrogen cycle. Living organisms acquire nitrogen from incorporation of NH4 into organic molecules.

Based on a review of published and grey literature on this issue, it can be concluded that the ban of mineral N-fertilisers and synthetic pesticides on the one hand, and the low level of nitrogen cycling within the farm because of low livestock densities on the other, are important contributions which organic farming makes to water protection. 

The nitrogen cycle entails formation of ammonia by bacterial fixation of N2, nitrification of ammonia to nitrate by soil organisms, conversion of nitrate to ammonia by higher plants, synthesis of amino acids from ammonia by all organisms, and conversion of nitrate to N2 by denitrifying soil bacteria. 

Figure 24-1 The nitrogen cycle. Conversion of N2 (oxidation state 0) to NH4+ by nitrogen-fixing bacteria, assimilation of NH4+ by other organisms, decay of organic matter, oxidation of NH4+ by the nitrifying bacteria Nitrosomas and Nitro-bacter, reduction of N03 and N02 back to NH4+, and release of nitrogen as N2 by denitrifying bacteria are all part of this complex cycle.1...

Glutamine synthase is just one of the links in the nitrogen cycle whereby nitrogen passes through several chemical forms. The passage of nitrogen from one form to another involves a chain of widely distributed organisms (fig. 21.6). 

Nitrogen cycle. The passage of nitrogen through various valence states, as the result of reactions carried out by a wide variety of different organisms. 

Tabtoxin J is a dipeptide exotoxin produced by Pseudomonas tabaci, the organism responsible for the wildfire disease of tobacco plants [141]. When hydrolyzed by peptidase, in vivo, this exotoxin releases tabtoxinine-p-lactam K, which inhibits Glutamine synthetase of the photorespiratory nitrogen cycle, causing chlorosis and death of tobacco plants [142]. 

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