1. Study subjects
The mean age of the 89 participates was 9.75 ±1.92 years (ranging from 5.5 to 14.3 years) and 55.06% were boys. The majority (73.03%) were obese based on BMI, and 26.97% had normal BMI.
Based on puberty status, the subjects were divided into non-pubertal group (n=42, 66.7% male) and pubertal group (n=47, 44.68% male). The average age was 8.36 ±1.64 years and 10.99 ±1.15 years, respectively. There was no statistical difference in BMI-Z scores or dietary habits between the two groups (p=0.783 and 0.641, respectively). The non-pubertal group was further subdivided into a younger children group (n=18, 66.7% male) and pre-pubertal group (n=24, 66.7% male). And the pubertal group classified as early (n=18, 77.8% male), middle (n=14, 35.7% male), late (n=15, 13.3% male). Of the 40 girls, 21 had E2 measured, 2 were non-pubertal with a level of E2 <5pg/ml, and 19 were pubertal with a level of E2 33.68±35.80 pg/ml; 21 of the 49 boys had T measured, 6 were non-pubertal with a level of T 5.10±4.16 ng/dl, and 15 were pubertal with a level of T 83.20 ±98.55 ng/dl. There was no statistical difference in BMI-Z scores, mode of birth, feeding patterns or dietary habits among the groups (p>0.05). Table 1, 2 and Table S1 describes the characteristics of the subjects.
2. Core microbiota in all the subjects
(1) Core microbiota
With 16S ribosomal RNA gene sequencing, 671 discrete bacterial taxa (OTUs) were identified. Most of these species belonged to the “shared” category of those common to multiple but not all samples. We also identified a “core” of 557 species shared among all fecal samples. The non-puberty group had 49 unique species and the puberty group had 66 unique species (Figure 1). The core microbiota were dominated by phylum Firmicutes, Bacteroidetes and Proteobacteria in both the non-pubertal and pubertal groups (Figure2 and Table S2).
(2) OTU classification with different puberty status
Using PLS-DA, the non-pubertal and pubertal groups can be distinguished to a certain extent, suggesting that the two groups differed in the classification of the gut microbiota (Figure 3).
3. Microbiota profiles with different puberty status
(1) Alpha- and beta-diversity in subjects with different puberty status
Regarding alpha-diversity, the Shannon diversity index, Observed OTUs, Faith’s phylogenetic diversity and Pielou’s evenness based on OTU distribution (groups of closely related individuals) there was no significant difference between pre-pubertal and pubertal groups (all p >0.05, Table S3).
Beta-diversity also did not differ significantly between these two aforementioned groups after correction for multiple testing (Table S4).
(2) Bacterial taxa differences in subjects with different puberty status
We used STAMP (Welch’s t-test) analysis to identify bacteria where the relative abundance was significantly increased or decreased in each phenotypic category. Non-pubertal subjects had members of the genus Turicibacter that were significantly more prevalent than puberty subjects, the proportion of sequence were 0.08±0.14% vs 0.02±0.04%, respectively (p=0.012, Figure 4 A). Also, the pubertal subjects had members of genus Sutterella that were significantly more prevalent than the non-pubertal subjects, the proportion of sequence were 1.92±3.27% vs 0.77±1.34%, respectively (p=0.034, Figure 4 B).
4. Microbiota profiles during puberty transition
(1) Alpha-, beta-diversity and bacterial taxa differences in non-puberty subgroups
As for the alpha-diversity between younger children and pre-pubertal groups, the Shannon diversity index, observed OTUs, Faith’s phylogenetic diversity and Pielou’s evenness based on OTU distribution, there was no statistical difference (all p>0.05, Table S3).
Beta-diversity also did not differ significantly between these two groups. None of the comparisons were significantly different (all p>0.05) after correction for multiple testing (Table S4).
STAMP (Welch’s t-test) found no differential bacterial taxa between pre-puberty group and non-puberty group (p>0.05).
(2) Alpha-, beta-diversity and bacterial taxa differences in puberty subgroups
As for the alpha-diversity between the three subgroups at the different puberty stages, the Shannon diversity index, observed OTUs, Faith’s phylogenetic diversity and Pielou’s evenness based on OTU distribution, there was no significant differences (all p>0.05, Table S3).
Beta-diversity also did not differ significantly between the three subgroups (all p> 0.05) after correction for multiple testing (Table S4).
STAMP (ANOVA methods) revealed that among early, middle and late puberty groups, the proportion of the genus Anaerotruncus increased gradually in association with the puberty stages (0.005±0.008%, 0.010±0.011%, and 0.033±0.049%, respectively). The proportion of the genus Coprococcus first increased, and then waned to a similar proportion with early puberty group (0.005±0.008%, 0.010±0.011%, and 0.033±0.049%, respectively). Differences among groups were statistically significant (p=0.025 and 0.025, respectively, Figure 5).
Spearman correlation analysis was used to detect an impact of BMI-Z on genera Anaerotruncus and Coprococcus: Genus Coprococcus did not correlate with BMI-Z (r=-0.025, p=0.865), whereas genus Anaerotruncus related to both BMI-Z and Tanner staging (r=-0.326 and 0.327, p=0.025 and 0.025, respectively). After further correcting BMI-Z, the correlation between genus Anaerotruncus and Tanner stage was slightly more robust (r=0.350, p=0.017).
(3) Alpha-, beta-diversity and bacterial taxa differences in non-puberty and puberty subgroups
Regarding the Alpha-diversity between the pre-puberty and the early puberty groups, the Shannon diversity index, observed OTUs, Faith’s phylogenetic diversity and Pielou’s evenness based on OTU distribution did not reveal any significant difference. Comparing the younger children group and the late puberty group, the Alpha- diversity indexes did not differ (all p>0.05, Table S3).
Beta-diversity also did not differ significantly between the three subgroups according to the puberty stages. The results were non-significant (all p>0.05) after correction for multiple testing (Table S4).
STAMP (ANOVA methods) showed that among non-puberty, early, middle and late-puberty groups, the proportion of the genus Butyricicoccus progressively increased, and then waned toa similar proportion with non-puberty group (0.27±0.23%, 0.30±0.26%, 0.70±0.85% and 0.28±0.22%, from non-pubertal, early-pubertal, middle-pubertal to late-pubertal, respectively). The proportion of the genus Sutterella increased steadily associated with puberty stages (0.77±1.34%, 1.26±1.92%, 1.63±3.96% and 3.00±3.57%, from non-pubertal, early-pubertal, middle-pubertal to late-pubertal, respectively), and the difference among groups were statistically significant (p=0.013 and 0.039, respectively, Figure 6).
Spearman correlation analysis was used to assess the impact of BMI-Z on the genera Butyricicoccus and Sutterella. Both genus Butyricicoccus and Sutterella did not correlated with BMI-Z (r=-0.079 and -0.131, p=0.459 and 0.222, respectively).
5. Correlations Between Sex hormone and Bacterial Abundance
To evaluate correlations between bacteria and serum sex hormones (testosterone and estradiol), Spearman’s rank analysis was adopted. In the pubertal subjects, the abundance of genera Adlercreutzia and Dorea was positively associated with the level of testosterone (r=0.293 and 0.545, p=0.046 and 0.002, respectively), and the abundance of genera Parabacteroides and Clostridium was positively associated with the level of testosterone (r=-0.383 and -0.361, p=0.033 and 0.046, respectively). There was no association between the bacterial abundance and serum estradiol (all p>0.05).