Both bacteria and viruses possess circular chromosomes which can be opened up under appropriate conditions. If the "buckle points" in both forms are identical, then it is possible for a viral chromosome to incorporate itself into bacterial DNA. This process is depicted at the right along with the normal lytic cycle of viral particles.
You will note two bacteria cells and two virus particles. Why dont we call viruses cells? The bacterial chromosome is depicted by a heavy line, the viral chromosome by a thin line. Flip to the next card to see the attack phase.