The hallmark of all living things is the ability to reproduce. A bacterium reproduction is simply another enzymatic behavior. An enzyme called DNA polymerase, along with several other enzymes that work alongside it, walks down the DNA strand and replicates it. In other words, DNA polymerase splits the double helix and creates a new double helix along each of the two strands. Once it reaches the end of the DNA loop, there are two separate copies of the loop floating in the E. coli cell. The cell then pinches its cell wall in the middle, divides the two DNA loops between the two sides and splits itself in half.
Under the proper conditions, an E. coli cell can split like this every 20 or 30 minutes! The enzymatic process of growing the cell, replicating the DNA loop and splitting happens very rapidly.
For more information, see How Human Reproduction Works.