Spearman’s correlations of the IBS symptoms with the copy numbers of total bacterial 16S rRNA genes and genes indicative of the different hydrogenotrophic functional groups indicated that total bacterial 16S rRNA genes and acsB were negatively correlated with the IBS symptom severity score (IBS-SSS), anxiety, and depression but positively correlated with IBS-QoL and its subindices at T1 (Fig. 2). The gene discussed is SLC27A5; the disease is major depressive disorder.