Final answer:
The integration of phage DNA into bacterial chromosomes is primarily due to identical DNA sequences between phage and bacteria, which allows for incorporation and recombination of genetic material, particularly during the lysogenic cycle and specialized transduction.
Step-by-step explanation:
The integration of phage DNA into the bacterial chromosome occurs because of identical DNA sequences in both the phage and the bacterial chromosome. Bacteriophages can have a lytic or lysogenic cycle. In the lysogenic cycle, a phage integrates its DNA into the host genome, and this process can lead to genetic diversity through recombination. During specialized transduction, which occurs after prophage excision in the lysogenic cycle, the phage DNA can accidentally take with it adjacent bits of bacterial chromosome DNA when it is excised, and this DNA may be transferred to another bacterium on infection.
Specialized transduction is responsible for the transmission of specific pieces of bacterial DNA if the prophage is incorrectly excised from the bacterial chromosome. Contrastingly, generalized transduction can occur during the lytic cycle when a phage accidentally packages host DNA instead of its own, resulting in the transfer of random bacterial DNA segments.
Environmental stressors, such as ultraviolet light or chemical exposure, can lead to the induction of the lysogenic cycle, thus increasing the chance of phage-mediated DNA integration. Lysogenic conversion is a significant process in the context of bacterial virulence and resistance, such as when nonpathogenic bacteria acquire toxin genes, becoming pathogenic.