I noticed that M9 minimal media is clear at the time of inoculation with bacteria, but around five hours after induction (i.e. around ten hours after inoculation with seeding culture) I see that the media turns a distinct greenish yellow colour. Any explanation for this observation?
Hi Aditya,
It could be pigments that bacteria secrete in the extracellular medium. Do you see this with any kind of bacteria? And what do you mean by "induction" exactly?
Cheers,
Thibault
@ Thibault G Sana: Thank you sir for the response. Part of my work requires over production of heterologous protein in bacterial system. I use IPTG to induce over-expression of the protein of interest. That is what I meant by induction. I use only BL21(DE3) strain of E.Coli so I haven't really looked at other strains of bacteria in this regard.
Does it still turn yellowish-green if you don't induce, or happens in an empty vector control? If it doesn't, then the likely culprit is the heterologous protein (are you expressing a flavoprotein?).
@ Alejandro Martin: Thank you sir for your response. Two of my colleagues (working with two different proteins) also observed similar change in colour around four to five hours after induction with IPTG. So perhaps it isn't very protein specific? I don't know enough right now to comment upon this though. Perhaps any protein when over-expressed somehow triggers this phenomenon? And no the protein I was working with when I first saw this wasn't a flavoprotein. Are flavoproteins somehow more likely to cause this?
Also I haven't checked properly whether the colour changes if induction is not done. I will look into that angle next time. May be IPTG itself is a cause?
Thank you once again for the response.
Dear Aditya,
There may be growth of some pigment producing bacteria. As the growth increases, the colour of the culture media might change. If you considered control (any non-inoculated flask) for you experiment? Please check it. Sometimes over production of certain metabolites may also contribute in altering the media characteristics. I think you should repeat the experiment with replicates and control as for comparing the replicates.
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