find out all the microbes involve in nitrogen cycle
Answers
Answer:#BAL arious processes are responsible for recycling the chemicals necessary for life on Earth. The nitrogen cycle is the most complex of these. Carbon, sulfur and phosphorus are the other main cycles. In this article we explore how nitrogen is cycled and the important role of microbes in this cycle.
Nitrogen is required by all living organisms for the synthesis of organic molecules such as amino acids, nucleic acids and proteins. The Earth’s atmosphere contains almost 80% nitrogen gas. It cannot be used in this form by most living organisms until it has been fixed, that is reduced (combined with hydrogen), to ammonia. Green plants, the main producers of organic matter, use this supply of fixed nitrogen to make proteins that enter and pass through the food chain. Micro-organisms (the decomposers) break down the proteins in excretions and dead organisms, releasing ammonium ions. These two processes form part of the nitrogen cycle.
The nitrogen cycle
The nitrogen cycle is the movement of nitrogen between the earth and the atmosphere. It consists of a series of processes that convert nitrogen gas to organic substances and these back to nitrogen in nature. It is a continuous cycle maintained by the decomposers and other bacteria. The nitrogen cycle can be broken down into four types of reaction and micro-organisms play roles in all of these (see Table 1).
Nitrogen fixation
Nitrogen gas is composed of two atoms of nitrogen linked by a very strong triple bond. This makes it chemically unreactive and large amounts of energy are required to break the bond. Nitrogen gas can be fixed in three ways.
Atmospheric fixation. This occurs spontaneously by lightning; only a small amount (5–8%) is fixed this way. Lightning allows nitrogen and oxygen to combine to produce various oxides of nitrogen. These are carried by the rain into the soil where they can be used by plants.
Industrial fixation. The Haber–Bosch process is used to make nitrogen-containing fertilizers. This is a very energy-inefficient process.
Biological fixation. Nitrogen-fixing bacteria fix 60% of nitrogen gas in the atmosphere.
Biological fixation
The reduction of nitrogen gas to ammonia is energy-intensive. It requires 16 molecules of ATP and a complex set of enzymes to break the bonds so that the nitrogen can combine with hydrogen. Its reduction can be written as:
N2 + 3H2→ 2NH3
Relatively few bacteria (the nitrogen-fixing bacteria) are able to carry out this reaction. Fixed nitrogen is made available to plants by the death and lysis of free-living nitrogen-fixing bacteria or from the symbiotic association of some nitrogen-fixing bacteria with plants.
Table 1. Reactions of the nitrogen cycle.
Reaction Micro-organism Conditions Process
Nitrogen fixation Nitrogen-fixing bacteria, e.g. Rhizobium Aerobic/anaerobic The first step in the synthesis of virtually all nitrogenous compounds. Nitrogen gas is fixed into forms other organisms can use.
Ammonification (decay) Ammonifying bacteria (decomposers) Aerobic/anaerobic The decomposers, certain soil bacteria and fungi, break down proteins in dead organisms and animal wastes, releasing ammonium ions which can be converted to other nitrogen compounds.
Nitrification Nitrifying bacteria, e.g. Nitrosomonas, Nitrobacter Aerobic Nitrification is a two-step process. Ammonia or ammonium ions are oxidized first to nitrites and then to nitrates, which is the form most usable by plant.
Denitrification Denitrifying bacteria Anaerobic Nitrates are reduced to nitrogen gas, returning nitrogen to the air and completing the cycle.
Explanation:
The transformation of nitrogen into its many oxidation states is key to productivity in the biosphere and is highly dependent on the activities of a diverse assemblage of microorganisms, such as bacteria, archaea, and fungi.