Yes atleast in flies says a news article in the Scientific American October 2007 issue. Experiments were performed with flies which were cleaned of all bacteria on them and were provided with un-contaminated food (devoid of any bacterial life forms) and compared with normal flies in regard to lifespan. Surprisingly no significant difference was observed within the groups. It is a widespread idea that microbes that live off a host, ideally utilize energy from the host and therefore might cause shortening of their lifespans. Yet this study proves that this notion is not completely true, atleast in flies. Ofcourse this kind of an experiment is not possible on higher organisms (human) which harness several capabilities of the microbial fauna present within. So it seems that nature isn’t ruthless after all 😉