Supplementary Figures Supplementary Figure 1. 1 Supplementary Figure 2. The effect of antibiotics on the relative abundance of Clostridium cluster XIVa. 2a) The abundance of Clostridium cluster XIVa is significantly lower (LME: p=0.02) in samples that have been collected after antibiotics intake (n=13, average time between antibiotics and sampling 7 weeks) than in samples without antibiotics(n=70). Samples more than 1.5 times above the upper quartile or below the lower quartile are denoted by circles. 2b) In the follow-up samples in average 25 weeks after the cessation of antibiotic usage the abundance difference is not significant when compared to the baseline or the first sample after antibiotic course (LME p=ns). Data shown from 6 subjects from whom all 3 samples were available. 2 Supplementary Figure 3. The relative abundance of bifidobacteria. Differences between the age categories of children are not significant (dashed line describes LME fit, p=ns), but all are significantly higher than in adults (p<0.05 in all comparisons, Wilcoxon rank-sum test). Samples more than 1.5 times above the upper quartile (3rd quartile) are denoted by circles. 3 Supplementary Figure 4. The relative abundance of phylum-level groups. In children, the increased relative abundance was only observed in Clostridium clusters IV (d, LME, p=0.053) and XI (e, LME, p=0.003), whereas no change was observed in the other phylum-level groups. Statistical significances between age categories in children and adults were assessed by 4 Wilcoxon rank-sum test and Benjamini-Hochberg p-value correction. Samples more than 1.5 times above the upper quartile (3rd quartile) are denoted by circles. 5 Supplementary Figure 5. The relative abundance of Akkermansia spp. in different age categories. The relative abundance of Akkermansia spp. does not change during 1-5 years of age (LME: p=ns), and is at similar level as compared to adults. Samples more than 1.5 times above the upper quartile (3rd quartile) are denoted by circles. 6 Supplementary Figure 6. The stability of two main sub-groups of Bacteroidetes: Bacteroides (panel a) and Prevotella spp. (panel b). The stability is assessed by Pearson correlation between consecutive time points from oligo-level data. Each point plotted represents the older age in the pair compared. The time interval between the first plotted time point and the baseline sample is four months. Samples from the same individual are connected by solid lines. The development of stability is estimated by linear mixed effects model, and indicated by the dashed line. The profile similarities of Bacteroides spp. (p=0.03) increase from 1 to 5 years, while no change is observed in Prevotella spp. (p=ns). 7 Supplementary Figure 7. The inter-individual similarity of microbiota in different age categories. In each age category, the similarities are calculated by Pearson correlation between individuals. Children in 3-4Y category have higher inter-individual similarity as compared to the other age categories (p<0.05, Wilcoxon rank-sum test). 8 Supplementary Figure 8. The relative abundance of core microbiota in different age categories. No significant difference between the age categories was observed (p=0.08, Kruskal-Wallis test). Samples less than 1.5 times below the lower quartile (1st quartile) are denoted by circles. 9 Supplementary Figure 9. The relative abundance of butyrate-producing bacteria in different age categories. The relative abundance of butyrate-producing bacteria increases significantly from 1 to 5 years (LME: p=0.02), but is not significantly different from adults, mostly due to large variation in the adult cohort. Samples less than 1.5 times below the lower quartile (1st quartile) are denoted by circles. 10