Nitrogen-Fixing Bacteria.

          When examining the nitrogen cycle, one particular type of microorganism known as nitrogen-fixing bacteria presents itself as “of increasing concern” to climatologists and microbiologists.  Nitrogen-fixing bacteria are significant to the nitrification reaction of the nitrogen cycle by converting nitrogen gas into more useful compounds such as ammonia (NH₃).  Ammonia, in addition to being more biologically accessible, is also used by nitrifying bacteria to produce nitrates and nitrites, two of the main greenhouse gases.   Denitrifiers and the natural limit of the nitrogen cycle formerly regulated the availability of nitrites and nitrates in the atmosphere - what happened?  Human activities.

            The natural limit of the nitrogen cycle has been greatly influenced by events of the nineteenth and early twentieth centuries such as the Industrial Revolution and World War I.  Some factors, which have prompted the increase in the natural limit of the nitrogen cycle include:

• Large-scale burning of fossil fuels initiated the release of higher levels of nitrogen oxides, including nitrous oxide.
• The development of the Haber-Bosch process, which allowed inert nitrogen gas to be converted into ammonia without the use of slow nitrogen-fixing bacteria.
• Increased ammonia production led to the production of cheap fertilizers that could be used on crops.
• Deforestation
• Production of nylon.

The increase in the natural limit of the nitrogen cycle has allowed a greater release of nitrates and nitrites into the Earth’s atmosphere, affecting the environment and human health.  Some of the more prominent effects due to the increase in nitrous oxide in the atmosphere include: 

• The destruction of the ozone layer
• Heightened exposure to UV radiation and risk of skin cancer and cataracts
• Formation of smog, causing respiratory problems, lung damage, increased risks of cancer, and a decrease in the efficiency of immune response.
• Global Warming

Nitrous oxide is a potent greenhouse gas and maintains a significantly larger global warming potential than that of carbon dioxide despite its considerably smaller concentration in the atmosphere.  As such, even the smallest increase in the levels of nitrous oxide in the atmosphere could result in drastic, irreversible outcomes. 

            To conclude, it would be incorrect to say that nitrifying bacteria alone has contributed to climate change..  It instead would be more scientifically accurate to state that nitrogen-fixing bacteria due to the existence of certain human activities are greatly influencing climate change through the release of higher amounts of nitrous oxide to satisfy the elevated natural nitrogen cycle limit.

The Nitrogen Cycle.

The diagram depicted below is a detailed illustration of the nitrogen cycle.

A summary of the six steps of the nitrogen cycle:

1. Plants using diffusion and active transport absorb nitrate ions. Nitrogen is required for the synthesis of proteins and other compounds in plants. The nitrogen compounds are passed through the food chain as other organisms feed on the plants and each other.  Waste products such as undigested food, urine and feces and dead organisms are added to the soil, as they contain nitrogen compounds.)
2. Ammonification:  Decomposers release ammonium ions once the proteins of dead organisms and animal wastes are broken down.
3. Nitrification: Conducted by nitrifying bacteria. Oxidation of ammonia or ammonium ions yields nitrites first and then nitrates.
4. Denitrification:  Denitrifying bacteria reduce nitrates to nitrogen gas.
5. Nitrogen fixation:  The first step in the synthesis of nitrogenous compounds.  Two types:
• Atmospheric fixation:  A spontaneous process carried out via lightning. Only small amounts of nitrogenous compounds are fixed in this way.
• Industrial fixation: Also known as the Haber process; An energy inefficient process used in the production of nitrogen fertilizers.
6. Biological fixation:  Sixty percent of nitrogen gas is fixed by nitrogen fixing bacteria.  Nitrogen fixing bacteria thrive in the root nodules of legumes, while others are free living in the soil.

It is important to note that microorganisms are significant to all five of the reactions of the nitrogen cycle:  ammonification, nitrification, denitrification, nitrogen fixation, and biological fixation.  As such, it can be concluded that microorganisms play a vital role in making nitrogen available for living organisms prior to its transport into the atmosphere.