Mobilization of vitamin B₁₂ transporters alters competitive dynamics in a human gut microbe

The functional and genomic diversity of the human gut microbiome is shaped by horizontal transfer of mobile genetic elements (MGEs). Characterized MGEs can encode genes beneficial for their host's self-defense (e.g., antibiotic resistance) or ability to compete for essential or limited resources (e.g., vitamins). Vitamin B₁₂ and related compounds (corrinoids) are critical nutrients that enable colonization by members of the common gut microbe phylum, the Bacteroidetes. Herein, we identify a distinct class of MGEs in the Bacteroidetes responsible for the mobilization and exchange of the genes required for transport of corrinoids, a group of cyclic tetrapyrrole cofactors including vitamin B₁₂ (btuGBFCD). This class includes two distinct groups of conjugative transposons (CTns) and one group of phage. Conjugative transfer and vitamin B₁₂ transport activity of two of the CTns were confirmed in vitro and in vivo, demonstrating the important role MGEs play in distribution of corrinoid transporters in the Bacteroidetes.