That doesn’t really work; it would be like a human trying to acquire resistance to being riddled with bullets. Strong UV is more or less a sort of machinegun if

That doesn’t really work; it would be like a human trying to acquire resistance to being riddled with bullets. Strong UV is more or less a sort of machinegun if you’re a microorganism. You can produce more of your existing defenses, but it will be so far from what’s required to gain a reproductive advantage that you won’t evolve. Maybe you could induce resistance to very brief exposure, but that’s it.