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If you had an isolate bacteria sample how would you determine if they were nitrogen fixing?

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Would stable isotope probing be useful? – Eekhoorn Jan 19 '13 at 16:42
@zenbomb more of a comment than an answer :) – Rory M Jan 19 '13 at 16:50

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up vote 2 down vote accepted

Never mind found the answer myself you can use the acetylene reduction assay.

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as a quick screen, often nitrogen fixing bacteria die or stop fixing nitrogen when exposed to oxygen. – shigeta Jan 19 '13 at 15:35
This is true, nitrogenase has a very low half life in the presence of oxygen- around 30 seconds. Never thought of that could be useful for further lab testing... Thanks. – Ben Jan 19 '13 at 20:08

I'd suggest doing a bioinformatic search of the bacterial genomes first before doing the experiments. You should be able to find homologues of the "nif" (nitrogen fixation) genes there.

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Not ideal if you have no idea what the colony is at all though. – Ben Jan 19 '13 at 20:09

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