Buttery Popcorn Odor in Contaminated Expression Prep

[ic3reyes]

Hello,

 

I am trying to overexpress my protein of interest using standard recombinant bacterial expression techniques of batch fermentation in shaker flasks. I have had this problem twice in the past 3 years, where a prep will appear to grow very slowly, then will suddenly flourish 24-48 hours after it is started. The media will turn a yellowish color and smell very strongly of buttered popcorn, and the resulting cell pellet will be much darker in color than the usual E. coli pellet. Oh yeah, and I'll get no protein out of my prep. I'm curious whether anyone knows what common bacteria/fungus/yeast/whatever could possibly get into a culture containing antibiotics and take it over. Has anyone else experienced this phenomenon? Is this something I can prevent in the future in some way?

 

Thank you in advance,

Chris

Graduate Student

University of Arizona

[John Cuthber]

I'm fairly sure that diacetyl (which smells like that and is yellow) is a by-product of ordinary yeast fermentation- it's found in beer in small quantities early in the fermentation but is reduced to butane diol later on during maturation of the beer.

Could ordinary yeast be getting into your fermenter?