great popular science review on the microbiome world 
 brings us from some basic biological concepts with a bit of historical timeline, add in the current understanding across the plant and animal kingdoms of the complex relationship between a macroscopic living entity and the ecosystem of symbiotic (and dysbiotic) organisms. 
 really delivers good overview, get the sense the field is on the cusp of exploding, seems there is so much more that we don't yet understand - which is frightening when you consider how we are impacting ecosystem of the world and our own microbiotic ecosystem. 
 for an excellent, more detailed review check Will Byrne here