Asked by: Tom Crawfurd, Littlehampton
Bacteria don’t have a fixed lifespan because they don’t grow old. When bacteria reproduce, they split into two equal halves, and neither can be regarded as the parent or the child. You could say that so long as a single one of its descendants survives, the original bacterium does too.
Individual bacteria can also turn themselves into spores with a tough coat to protect themselves from dry conditions. Bacterial spores have been successfully revived from 250-million-year-old salt crystals found in New Mexico in 2000.
But if we assume that the global bacteria population is stable, then it follows that one bacterium must die for each new one that is produced. Bacteria divide somewhere between once every 12 minutes and once every 24 hours. So the average lifespan of a bacterium is around 12 hours or so.