Hey Kedar,

I'm not sure if this applies to your case, but... I have some marine isolates that have the ability to do the same thing on agar nutrient medium. They produce some sort of diffusible pigment that change the color of the plates to a reddish one even though the colonies are pale cream. Maybe your isolate is also producing some pigment?

Thanks Liany! Have you identified your marine isolates?

I was thinking more on the lines of Serratia and will try to PCR genotype it if necessary.

I only performed 16S rDNA analysis, that showed my isolates belong to the genus Bacillus. I am still working on finishing the identification to species level.. =/

Many bacteria excrete compounds in to the medium.

If you want to be sure you can extract soluble compounds from the agar (w/wo the isolate) and do some basic chemical finger print (e.g. hplc-ms)

Thanks Ray!