Bacterial colonization is a useful argument for interrogating the "we must colonize spaaaace!" folks' intentions. I mean, why exactly must we colonize space?
"Before the sun leaves the main sequence of the Hertzsprung-Russell diagram/the Earth is hit by a comet or irradiated by a GRB" is a meaningless argument. These events happen on a time frame of hundreds to thousands of megayears; while the mean life expectancy of a mammalian species is on the order of one to ten MYa, and for a hominid species like us, it's well under one MYa. These arguments don't hold water. Furthermore, we coevolved with our biosphere and we're really badly adapted to existence without a large subset of it: calling for human space colonization is implicitly a call for terraforming/transporting a viable terrestrial biosphere to other worlds. Which brings us neatly back to bacterial colonization, because that's part of the package deal.
While I can't refute the quasi-religious imperative implicit behind the rhetoric for space colonization, I wish its proponents would recognize that it's essentially a faith-based ideology!