The picture of the microbiome that emerges from the study of Caporaso and colleagues is one of volatility. At each body site, there are relatively few taxa that are present throughout the entire sampling period. Rather, most taxa are classified as either persistent, being detectable in many consecutive samplings before disappearing, or transient, being found for only short periods of time. One has the image of the persistent organisms blooming to high numbers, only to retreat until they bloom again. All of this is amidst a flux of short-term visitors to the community.
Another interesting characteristic is that taxa within persistent and transient categories can be different, allowing these communities to be distinguished. In the two subjects studied, the stool microbiomes of both persistent and transient communities had few predominant taxa: the Clostridia, Bacteroidia and, in one subject, Erysipelotrichi. However, the persistent and transient communities in both subjects could be differentiated by the presence of Betaproteobacteria and Deltaproteobacteria in persistent communities, while transient communities uniquely contained Gammaproteobacteria and Bacilli. In one subject, Actinobacteria, Epsilonproteobacteria and Verrucomicrobia were also unique to the transient community. The tongue and palms had many more predominant taxonomic classes, but none of these taxa clearly differentiated persistent and transient communities consistently across the two subjects.
Despite this mercurial community structure, the communities of the three different habitats remain distinguishable from each other at all times. This suggests that the players in each community, and the bounds on their abundances and half-lives, are some of the differentiating characteristics of each body habitat.