Four weeks of arsenic treatment (10 ppm in the drinking water) to wild-type and IL10−/− mice (who can develop colitis depending on the resident gut microbiota) resulted in genetic-dependent gut microbiome changes with an increase in Bacteroidetes but a decrease in Firmicutes in arsenic-treated IL10−/− mice (Lu et al., 2014b). The gene discussed is IL10; the disease is colitis.