We were all familiar with the concept that we carried around with us a load of microrganisms, some of which were helpful to us and some of which were harmful. But now we are encouraged to abandon this us-and-them point of view and regard a human being, a whole human being, a holobiont, as an entity comprising host and microbes. The human genome should be seen in the context of all the genomes of all the organisms which are part of a holobiont, this conglomerate genome being referred to as the hologenome.
Attempting to understand how the human body works without taking into account the attendant microbial communities can prove difficult because the whole system interacts in complex ways. We need to know what is happening in the holobiont to understand the workings of the human body.