Weighing in on the Hologenome-Metagenome Debate

We read with interest Eugene Rosenberg's letter on the terms holobiont and hologenome (March 2013, p. 101). We agree with his argument that the term hologenome is superior to metagenome when describing the total genetic material of a metazoan (or plant) and all of its associated symbiotic microorganisms, as these organisms are functioning as single unit, which we termed the symbiome. In this lexicon the hologenome is distinct from the metagenome which is used to describe an environmental sample of multiple species types that are not all functioning as part of a whole. We would point out that our use of the term hologenome (G. D. Ehrlich, N. L. Hiller, and F. Hu, Genome Biol. 9:225, 2008) actually slightly preceded that of the Rosenbergs in the literature, although the concept was clearly arrived at independently by our two groups.