How about: - bacteria with engineered enzymes for recycling (https://news.ycombinator.com/item?id=16856246 https://news.ycombinator.com/item?id=16856246) mutat

How about: - bacteria with engineered enzymes for recycling (https://news.ycombinator.com/item?id=16856246 https://news.ycombinator.com/item?id=16856246) mutate/go wild and wipe out most/all traces of civilization - what we can find today is just slightly elevated levels of whatever these bacteria mostly ignored.