E.coli cells lyse in minimal media - (May/01/2011 )

I have been growing various e.coli strains in minimal media (phosphate buffer, sugar, trace metals, amino acids), most of the strains originate from CGSC. I grow an overnight in minimal media and use that to inoculate a larger culture starting at an OD of ~0.01 and grow at 37 degrees. Sometimes the culture will get to an OD of ~0.5 , which is mid-log phase for the strain and media, and the cells begin to lyse. I can't figure why this is happening. None of the strains carriers pLysS and only some of the strains are DE3 lysogens - sometimes it happens in my wild type strain.

Does anyone have a suggestion on why this might happen?

Sounds like phage infection. Is the variation related to whether the strain is T1 phage resistant?

The different strains are gene knockout related to iron sulfur cluster assembly. We don't work with bacteriophage. We only have DE3 for order to do protein expression. Are phage just floating through the air all over the place?

As phage434 told it looks like Phage. Try to take new stock of then try once