Fig. 2

Gut microbial diversity differs between healthy controls and chronic obstructive pulmonary disease (COPD) patients. a Comparison of the operational taxonomic units (OTUs) in the three subject groups. b Relative proportions of bacterial phyla in the three subject groups. c–e Comparisons of the abundance of major bacterial families in the three subject groups. The x axis denotes relative abundance (%). The values on the x-axis are expressed as delta between the median relative abundance (%) of the right-side group and the median relative abundance (%) of the group on the left. Healthy, n = 73; COPD I–II, n = 67; COPD III–IV, n = 32. Significance was determined by ANOVA and by Kruskal–Wallis test, and p values were corrected using the Bonferroni method. *p < 0.05, **p < 0.01