Fig. 2

Ecological succession of microbiota steady states for the six MARS500 crewmembers over the entire mission simulation. For each crewmember, the temporal succession of the steady states, displayed as numbered boxes on the timeline (black arrow), is shown. Microbiota steady states were defined using a height threshold in individual hierarchical-Ward linkage trees, based on Jensen-Shannon distance. Box color is related to the dynamics of formation of the microbial structure of that steady state respect to the previous one, by evaluating the contribution of the individual microbial heritage and possible allochthonous microorganisms. Within each subject, for each steady state, except for the first one, the percentage of microbiota not deriving from the immediately preceding steady state was estimated using SourceTracker [34] and values were then normalized by a z-score approach. Higher values of z-score correspond to greater changes in the microbiota configuration with respect to the ordinary dynamics observed during the study (yellow/red boxes, see the color key on the top). Microbiota structures characterizing each steady state are displayed as Wiggum plot [13] of the most abundant OTUs, colored according to phylum membership as in Fig. 1a, grouped in co-abundance groups (CAO) (see Additional file 5: Figure S4). Steady state discriminatory OTUs were identified using Random Forests [12]; their taxonomy is shown above each Wiggum plot