E. coli bacteria, grown in $^{15}\text{NH}_4\text{Cl}$ medium for several generations, are then allowed to grow in $^{14}\text{NH}_4\text{Cl}$ medium. After 2 generations, the bacteria are isolated from the medium, and the DNA of the bacteria is centrifuged in CsCl. The result of the density gradient centrifugation of DNA is.