Dear Doroteja,

We work with fluorescent pseudomonads which produce a yellow siderophore which rapidly diffuses through agar. Strain 29 may be doing this - if you re-streak on normal media, or grow liquid coutures for long enough, do you see this yellow colour? If it is a siderophore (from a fluorescent pseudomonad) it is expressed when Fe becomes limiting and should look very fluorescent if you illuminate it with UV light, or even when you look at it in direct sun light. The colour will also be effected by free Fe (eg. FeCl3) and you can measure this quenching using a fluorescent spectrophotometer.

Regards, Andrew.

hello, dear Doroteja,

I did the same experiment when I was working on PGPR, I used chrome azurol S (cas) technique described by Schwyn and Neilands (1987).in brief, I inoculate 5ul of bacterial suspension (spot) on the surface of CAS solid medium, I incubate at 30deg 48-72 hours, I considered the bacterial strain siderophore positive when the blue color is turned to orange like your strain number 29.

I have also worked on sidephore producing bacteria, what I think is various organisms have various capacity or efficiency in producing Siderophore and solubilising iron in the media that is converting ferric form to ferrous and the orange colour is the result.

So, the colour and halo depends on the capacity of bacterial Siderophore to convert insoluble to soluble form.of iron. Therefore it may vary from organism to organism

It is evident that siderophores are produced by your strain # 29, and not by the others. As you point out, these are qualitative assays.

The level of Siderophore production is influenced by the medium in which the strain grows, and will be different from what occurs in a plant.

Have you published your results? I am particularly interested to find out what the percentage of siderophore producers is amongst the endophytes you isolate compared to strains you get from the rhizosphere and bulk soil.