Fig. 1

Richness and evenness of oral microbiome by alcohol drinking levels. a, b Violin plots of the number of observed species (richness) and inverse Simpson’s Index (evenness) in non-drinker, moderate drinker (MD) and heavy drinker (HD) groups. These indices were calculated for 500 iterations of rarefied OTU table with minimum sequencing depth of 1325 among all study subjects, and the average over the iterations was taken for each participant. Plotted are median, interquartile ranges, and the probability density of the indices at different values. Mean values of the richness in non-drinker, MD, and HD groups were 94.6, 100.1, and 100.3, respectively; mean values of the inverse Simpson’s Index in each group were 11.6, 12.3, and 12.1. One star (*) indicates p < 0.05 in linear regression model. c, d Rarefaction curves of number of observed species and inverse Simpson’s Index according to the number of reads per sample in non-drinkers, MD, and HD