This came out of a thought I had, that a large contributing factor to eventual human death is the human body, which throughout it's life is made to carry a large number of corrosive, toxic, bacterial fluids and substances. This got me thinking, would the human life-span (as well as quality of life) dramatically increase if we were to eventually manufacture nano-machines capable performing the various functions of healthy bacteria and slowly phasing out the natural bacteriums within our bodies - perhaps by using the machines not only to outperform the bacteria on specific tasks, but also to gradually kill them? One example of a benefit of replacing, say, intestinal bacteria with nano-technology would be the dissipation of methane production in the bowels, but there would be many others I'm sure, that's probably more a cosmetic reason. Do you think this would improve the human life-span and / or quality of life? I know it's a long way.