Final answer:
The second purification step in the context provided is anion exchange chromatography, which utilizes the differences in the negative charges of DNA to separate plasmid DNA from genomic DNA.
Step-by-step explanation:
The second purification step referred to in the question appears to be anion exchange chromatography, which is used for the purification of plasmid DNA. In this process, the negatively charged plasmid DNA is separated from the host's genomic DNA by using a silica-based anion-exchange column. The genomic DNA, being larger, has a higher negative charge than plasmid DNA, allowing it to bind more strongly to the column. Consequently, the plasmid DNA is eluted while the genomic DNA remains bound to the column.