Final answer:
In bacterial DNA replication, helicase is the enzyme responsible for separating the double-stranded DNA at oriC, while topoisomerase II or DNA gyrase relaxes the DNA ahead of the replication fork.
Step-by-step explanation:
In bacterial DNA replication, the enzyme that initially separates the double-stranded DNA (dsDNA) at the origin of replication, known as oriC, is helicase. Helicase unwinds the DNA just at the origin by breaking the hydrogen bonds between the nitrogenous base pairs, which requires energy in the form of ATP. Once the DNA strands are separated, single-strand binding proteins (SSBs or SSPs) bind to the strands, keeping them apart. In addition, topoisomerase, particularly topoisomerase II or DNA gyrase, acts ahead of the replication fork by changing the shape and supercoiling of the DNA, effectively relaxing it and allowing the replication process to proceed without the DNA becoming too tightly wound.