Replication begins at a single origin of replication on each DNA molecule and proceeds in both directions around the molecule. Copies made are distributed to daughter cells without any use of a mitotic spindle.
Mutations are a huge source of variability between and within species.
Recombination is also a source of variability. The sources may be chromosomes from two different bacteria. Specialized if due to improper detachment of prophage from bacterial chromosome. Plasmid DNA transfer may not result in recombination, but only in the acquisition of the plasmid by the recipient. Transposons are genes that can move to other sites on a DNA molecule or from one DNA molecule to another.