<p>Cbi, cobinamide; Cbl, cobalamin; Ado, adenosyl; DMB, dimethylbenzimidazole; NaMN, nicotinate mononucleotide. AdoCbl and tetrahydrofolate are essential cofactors of the <i>cmu</i> pathway <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0056598#pone.0056598-Studer1" target="_blank">[6]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0056598#pone.0056598-Studer3" target="_blank">[9]</a>. Transport and enzymatic reactions are shown with dotted and full arrows, respectively. Genes indicated in bold are located on the 380 kb plasmid pCMU01. Circled gene names encode proteins more abundant in chloromethane cultures. AdoCbl can be synthesized <i>de novo</i> by an aerobic biosynthesis pathway that incorporates cobalt (diamond), or obtained from a salvage pathway after internalization of preformed Cbi or Cbl. In prokaryotes, the cobalt needed for corrin ring synthesis may be incorporated into cells using the CorA transport system <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0056598#pone.0056598-Niegowski1" target="_blank">[69]</a>, the putative transmembrane proteins CbtA and CbtB <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0056598#pone.0056598-Rodionov1" target="_blank">[14]</a>, the Resistance-Nodulation-Division (RND)-type <u>C</u>o<sup>2+</sup>/<u>Z</u>n<sup>2+</sup>/<u>C</u>d<sup>2+</sup> efflux system CzcA <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0056598#pone.0056598-Goldberg1" target="_blank">[27]</a>, or the Icu transporter <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0056598#pone.0056598-Chou1" target="_blank">[70]</a>. The TonB-dependent Btu system imports preformed corrinoid compounds <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0056598#pone.0056598-Cadieux1" target="_blank">[28]</a>. We hypothesize that BluB-related proteins link AdoCbl and H<sub>4</sub>F <i>de novo</i> synthesis.</p
