Methanobrevibacter smithii is the predominant methanogen in patients with constipation-predominant IBS and methane on breath.
Kim G, Deepinder F, Morales W, Hwang L, Weitsman S, Chang C, Gunsalus R, Pimentel M. Methanobrevibacter smithii is the predominant methanogen in patients with constipation-predominant IBS and methane on breath. Dig Dis Sci. 2012 Dec; 57(12):3213-8.