If bacteria could build spaceships, they would colonize every planet they could get their hands on, every star system they could see. They would be unlikely to care about the welfare of the natives, or about what they would be destroying in the process. They would take and take, grow and grow, until they no longer could, if for no other reason than there was nothing left to take. Most life would. The only life that thinks twice about such things is us, and we're fuckin weirdos. :/