Percentage of accessory genes for 11 gut bacterial species. (a) The bars correspond to the percentage of accessory genes, which were calculated based on the asymptotic number originated from the exponential regression model. The values were estimated for the 11 gut bacterial species which are grouped according to their phyla. (b) Dot plot displays the relation between number of core genes or total number of genes and genome size. The graph shows that number of core genes also correlates with genome size; however the total number of genes grows faster with genome size than the number of core genes.