Hello Caroll!

That sounds very interesting.

-Medium has Fe in it (not declared)

-Your tools that contain Fe which came in contact with culture or media

-Source of extraction had Fe, especially if it is the first few streak

Finding more data would help.

-Would transferring a colony reduce the Fe concentration per cell?

-Have you tried in a different room that has different tools, supplies, air...?

I hope you get Fe free culture, good luck!

Well to explain this in short, one must remember the soil conditions where these organisms are growing. Many a time there is a bountiful of aerobic organisms which carries out many different types of metabolism to survive, then in the absence of limiting oxygen (which is the normal case in any soil) the next alternative terminal electron acceptor for these aerobes, is ferric ions or tetravalent manganese etc. May be this is one of the reasons why you see a spurt in ferric containing enzymes.

The thing is I have two conditions: Fe-replete (where I added exogenous Fe) and Fe-limited (no exogenous Fe was added, and instead EDTA was added to chelate it).

But the iron-containing enzymes are larger in my medium that is Fe-limited.

Also, the enzymes involved in the catabolism of the substrate that wasnt broken down during exponential growth was also increased.

Rightly so, it all points to the fact that the organism was searching for an alternate electron acceptor. Let me tell you that I too was unaware of such a fact till way back in the mid 1980s, I found that a strict heterotrophic aerobe - Pseudomonas aeruginosa, could grow in presence of ferric ion and tetravalent manganese in absence of oxygen. I tried the same experiment with a chemolithotroph - Acidthiobacillus ferrooxidans and found identical results. In fact I have published these findings then in Journal of Fermentation Technology from Japan. I give the reference below as:

J.Ghosh and K.Imai: (1985), Leaching mechanisms of manganese dioxide by using elemental sulfur by Thiobacillus ferrooxidans, J.Ferment.Technol., 63(3),259-263.

I would look to see if any of your bacteria are known SIDEROPHORE producers. Under low or limiting iron conditions certain bacteria produce siderophores (molecules that can easily strip iron out of EDTA and provide them to bacteria of that particular genus). There are tests that one can design that will let you know if any of the bacteria are likely producing these molecules in the media which might explain why you are seeing these results.

I too agree with Christopher....

Dear Caroll,

What an interesting experimental results. I wondered how much EDTA did you add into the Fe-limited condition? What was the efficacy of EDTA in chelating of Fe? What was the oxygen availability and pH along the incubation period? Is there any information detail about type, amount and flux of Fe-containing enzymes? What was major substrate? As those answers of the questions could be helpful for the interpretation since there are numerous Fe-enzymes such as mono- and dioxygenase which could involving in degrading substrate in oxic condition. And Fe-EDTA complex could be among those substrate that some microbes are capable to degrade with mono-/dioxygenase enzymes. In addition, EDTA favors to form complex with ferric ion and, in oxic condition, Fe2+ can be efficiently oxidized to Fe3+. However, with oxic condition it is possible for Fe-EDTA degradation. With anoxic condition, Fe-EDTA is quite persistent for degradation. Yet the Fe-EDTA can be degraded by catalase and H2S. by the way, catalase also contains four iron containing heme groups. Therefore, if the type, amount and flux of those Fe-containing enzymes were different, this might be resulted from EDTA.

I hope my sharing view may be useful for you. Thank you for inspiring results triggering my curiosity and digging for possible answer. :)

Cheers,

https://en.wikipedia.org/wiki/Category:Iron_enzymes

Article Biodegradation of Metal-EDTA Complexes by an Enriched Microb...

https://www.osti.gov/servlets/purl/967956

https://en.wikipedia.org/wiki/Catalase

Article Degradation Kinetics of Fe-EDTA in Hydrogen Sulfide Removal Process