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I read that rhizobium carry the enzyme nitrogenase, which is irreversibly damaged upon the exposure of oxygen. Inside the root nodule of legumes leg-haemoglobin keeps a microaerophilic environment where nitrogenase enzyme can function and molecular nitrogen can be fixed (source: Brock's Biology of Microorganisms).

Shouldn't therefore Rhizobium bacteria die in such microaerophilic condition inside the root nodules?

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  • $\begingroup$ Welcome to Bio. What makes you think rhizobia are anaerobic environments? $\endgroup$ – AliceD Mar 28 '17 at 13:36
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    $\begingroup$ I read that rhizobium carry the enzyme nitrogenase that is irreversibly damage upon the exposure of oxygen, that's why, inside the root nodule of legume plants leg-haemoglobin keeps a microaerophilic environment where nitrogenase enzyme can function and molecular nitrogen can be fixed. $\endgroup$ – Anindya Mar 28 '17 at 13:47
  • $\begingroup$ That's interesting to note. +1. I added those details in the question. If you could add the source of that info that would be awesome. Thanks for this question. $\endgroup$ – AliceD Mar 28 '17 at 14:04
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    $\begingroup$ The source is 'Brock Biology of Microorganism', it is 14e I believe $\endgroup$ – Anindya Mar 28 '17 at 14:33
  • $\begingroup$ Great book! I love that one, especially the edition with the hot water springs in Yellowstone NP :) $\endgroup$ – AliceD Mar 28 '17 at 14:42
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TLDR One hypothesis for survival is nitrate respiration.

Long Answer Ampount of oxygen available in root nodules is controlled by the host plant by two ways:

  1. By presence of leghemoglobin
  2. By the diffusion resistance Under anaerobic condition the bacteria survives by making use of denitrification process which could be used to produce ATP under anaerobic conditions.

It is known for a while that, beside nitrogenase activity, in many symbiotic associations between legumes and Rhizobium the activity of nitrate reductase also exists 12. Most of the nitrate reductase ativity has been found to be concentrated in infected bacterial body i.e., bacteriod3. The bacteriod uses the process of conversion of nitrate into nitrite for creating a proton gradient which is inturn used for generation of ATP. Nitrate respirationReference.

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  • $\begingroup$ Leghemoglobin fan here. My boy needs equal time with that loser nitrate reductase. Got another diagram? $\endgroup$ – Willk Mar 29 '17 at 0:02

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