[jennyp]

So when a bacterium has errors in gene replication, who gets the mutation, the original organism or the copy?

Normally in the copy. There can be damage or incorrect repair to the original, but normally, even in eukaryotes, replication errors are found in the copy.

Wait - when a bacterium divides, how do you tell which is the "original" and which is the "copy"? Aren't those concepts kind of moot here?

[Nebullis]

when a bacterium divides, how do you tell which is the "original" and which is the "copy"?

Each daughter cell ends up with one original and one copied strand of DNA. The original strands of DNA are copied by multiple polymerases. The copied strand will have the errors. A particular error will end up in only one daughter cell.