Approximately how long do bacteria live for?
They're effectively immortal, albeit in a Phoenix-rising-from-the-ashes sort of way.

In general, a bacterial cell will divide as soon as it's biochemically able to do so, leaving behind two daughter cells. Neither daughter cell is actually the same as the mother cell, so in one sense the mother cell will have "died". On the other hand, the daughter cells are genetically identical to the mother cell and all of the physical material present in each of the daughter cells at the moment right after they split came from the mother cell.