In: Biology
MICROBIOLOGY
Describe a mutualistic relationship between a eukaryotic host and a prokaryotic symbiont in detail. Explain what benefit each organism gets from the association? In the context of evolution by natural selection, do you think these relationships are likely to strengthen or weaken over time? Justify your answer
Nitrogen fixation is the process in which the N2 available in the atmosphere is converted to NH3 (chemically highly reactive molecule) by number of microorganisms is known as “nitrogen fixation”. Nitrogen fixation is carried out by free – living bacteria, cyanobacteria and Symbiotic bacteria. Organisms that are capable of fixing atmospheric nitrogen possess an enzyme known as “nitrogenase complex”. This nitrogenase complex consists of two proteins dinitrogenase and dinitrogenase reductase. The symbiotic bacteria Rhizobium is associated with leguminous plants. The plants provide nutrients and shelter and bacteria fix the nitrogen and supply to the plants.
A red heme – containing protein called leghemoglobin is found in the nitrogen – fixing root nodules of leguminous plants. The protein component is produced by the plant, whereas bacterial cells produce the precursor of heme. The oxygen toxicity problem inactivating nitrogenase enzyme in nitrogen fixing bacteria is solved by production of leghemoglobin. The leghemoglobin binds the all available oxygen in the plant root zone and creates an oxygen free environment that cannot interfere in nitrogen fixation, and efficiently delivers the oxygen through the bacterial electron – transfer system. Thus, leghemoglobin has an important function in nitrogen fixation in keeping up the nitrogenase activity and binding the oxygen.
The Rhizobia are attracted to leguminous plants and form nodules and in this process nod genes play a critical role. The nod genes are responsible for poroviding oxygen free environment for nitrogenase enzyme of Rhizobia. the Rhizobia in root nodules synthesize nitrogenase that facilitates the conversion of atmospheric nitrogen to nitrates and provide the to plants. Therefore, the mutual interaction between the plants and bacteria result in benefit of each other.
During course of evolution, the eukaryotic cells are evolved from prokaryotic cells developing membranes according to endosymbiotic theory. Therefore, the mutualistic association between prokaryotes and eukaryotes have been strengthening over period of time during evolution.