plant surface microbiology.pdf

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Galdino Andrade
organic nitrogen in the soil such as free-living ammonifiers and protozoans,
which also have an important function of mobilisation and mineralisation of
nitrogen compounds (Fig. 4). The choice of these groups within the nitrogen
cycle was based on their ability to produce ammonia as an end product. Both
the nitrogen fixers and the ammonifiers such as the protozoa release ammonia
into the rhizosphere. However, the pathway production is different: (1) the
first group uses atmospheric nitrogen that by biological fixation produces
ammonia, (2) the second group takes part in the mineralisation process of
nitrogen organic compounds and, (3) the third group, such as microorganism
predators, obtain proteins from their prey and excrete ammonia, among other
substances.
Atmospheric nitrogen fixation is a fundamental process for the maintenance
of the biosphere, as all organisms require proteins. Nitrogenase is an
enzyme complex which is responsible for nitrogen fixation and requires great
quantities of energy for its activity. Non-symbiotic biological fixation of
nitrogen is carried out by some free-living bacteria genera which are associ-
Protozoans
Feeding
Bacteria
Excretion
Microbiota
Proteins
Aminoacids
Excretion
Celular death
Proteases
Peptidases
Microbial
Mineralization
NH4 + N2
Nitrogen
fixation
Fig. 4. The activity of some functional groups of microorganisms in the nitrogen cycle