Hello!

I've been growing E. coli in LB, and to test whether the cells in the culture had been lysed I centrifuged them (5,000 rpm for 10 minutes) and then measured the absorbance spectrum of the supernatant. I found the DNA concentration in the supernatant was the same if I added detergent or not. At first I concluded that many of the cells must have gotten lysed, but I then measured the absorbance of pure LB and I got almost the same concentration of DNA.

Does this mean LB has DNA from the yeast extract? If so, what could be a simple way to test whether the cells are lysed beforehand or not?

Thank you very much