Figure 1.

Genomic distribution of hydrogenases in human colonic microorganisms. (A) The proportion of microbial species that encode hydrogenases. This was determined using the 343 microbial species represented in the Human Microbiome Project Gastrointestinal Tract (HMP GI) genome database. (B) Distribution of human colonic hydrogenase sequences by microbial phyla and hydrogenase class. Hydrogenase sequences were obtained from human colonic microorganisms represented in the NCBI Reference Sequence database and were classified according to previously-outlined criteria.¹⁹