- 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, S2 describes the characteristics of the subjects.
- Core microbiota in all the subjects
With 16S rRNA 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 (Figure 2 and Table S3).
- Microbiota profiles with different puberty status
(1) OTU classification
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).
(2) Alpha- and beta-diversity
Regarding alpha-diversity, there was no significant difference of the Shannon diversity index, Observed OTUs, Faith’s phylogenetic diversity and Pielou’s evenness based on OTU distribution between non-pubertal and pubertal groups (all p >0.05, Table S4).
Beta-diversity also did not differ significantly between these two aforementioned groups after correction for multiple testing (Table S5). By Distance method Bray-Curtis and Statistical method PERMANOVA, PCoA analysis illustrated that the gut microbiota samples from the non-pubertal group could not distinguish from the pubertal group [PERMANOVA] F-value: 0.712; R-squared: 0.008; p-value < 0.735 (Figure 4A).
(3) Bacterial taxa differences in subjects with different puberty status
We used Lefse analysis to identify bacteria where the relative abundance was significantly increased or decreased in each phenotypic category. Non-pubertal subjects had members of the Non-pubertal subjects had members of the order Clostridiales, Pasteurellales, family Clostridiaceae, genus Coprobacillus and Haemophilus that were significantly more prevalent than puberty subjects. Also, the pubertal subjects had members of class Betaproteobacteria, order Burkholderiales that were significantly more prevalent than the non-pubertal subjects(Figure 5).
Spearman correlation analysis was used to detect an impact of BMI-Z on class Betaproteobacteria, order Clostridiales, Pasteurellales, Burkholderiales, family Clostridiaceae, genus Coprobacillus and Haemophilus. The results showed the relative abundance of order Pasteurellales and genus Haemophilus correlate with BMI-Z (r=0.223 and 0.222, p= 0.036 and 0.036, respectively), whereas other differential bacterial taxa had no association with BMI-Z (p>0.05).
- 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, there was no statistical difference of the Shannon diversity index, observed OTUs, Faith’s phylogenetic diversity and Pielou’s evenness based on OTU distribution (all p>0.05, Table S4).
Beta-diversity also did not differ significantly between these two groups (all p>0.05, Table S5). By Distance method Bray-Curtis and Statistical method PERMANOVA, PCoA analysis illustrated that the gut microbiota samples from the pre-pubertal group could not separate partly from the younger children group [PERMANOVA] F-value: 0.389; R-squared: 0.0096; p-value < 0.982 (Figure 4B).
Lefse analysis 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 among 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 S4).
Beta-diversity also did not differ significantly among the three subgroups after correction for multiple testing (all p> 0.05, Table S5). By Distance method Bray-Curtis and Statistical method PERMANOVA, PCoA analysis illustrated that the gut microbiota samples from the three groups could not distinguish from each other group [PERMANOVA] F-value: 0.857; R-squared: 0.0375; p-value < 0.679 (Figure 4C).
Lefse analysis found no differential bacterial taxa among early-, middle- and late- puberty group (p>0.05).
(3) Alpha-, beta-diversity in non-puberty and puberty subgroups
The Shannon diversity index, observed OTUs, Faith’s phylogenetic diversity and Pielou’s evenness based on OTU distribution did not reveal any significant difference between the pre-puberty and the early puberty groups. Comparing the younger children group and the late puberty group, the Alpha- diversity indexes did not differ, either (all p>0.05, Table S4).
Beta-diversity also did not differ significantly between the pre-puberty and the early puberty groups, or the younger children group and the late puberty group. The results were non-significant after correction for multiple testing (all p>0.05, Table S5). By Distance method Bray-Curtis and Statistical method PERMANOVA, PCoA analysis illustrated that the gut microbiota samples from the early puberty group could not distinguish from pre-puberty group [PERMANOVA] F-value: 0.70375; R-squared: 0.01729; p-value < 0.698, and the gut microbiota samples from the late puberty group could not distinguish from younger children group, either. [PERMANOVA] F-value: 0.67589; R-squared: 0.021338; p-value < 0.801 (Figure 4D, E).
- 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, Ruminococcus and Dorea was positively associated with the level of testosterone (r=0.371, 0.471 and 0.488, p=0.040, 0.007 and 0.005, respectively), and the abundance of genera Parabacteroides and Clostridium was positively associated with the level of testosterone (r=-0.424 and -0.361, p=0.017 and 0.046, respectively). There was no association between the bacterial abundance and serum estradiol (all p>0.05).