Catalyzes the insertion of Co(2+) into sirohydrochlorin as part of the anaerobic pathway to cobalamin biosynthesis. To a lesser extent, is also able to insert Fe(2+) into sirohydrochlorin, yielding siroheme. Co-sirohydrochlorin + 2 H(+) = Co(2+) + sirohydrochlorin 2 H(+) + siroheme = Fe(2+) + sirohydrochlorin Cofactor biosynthesis; adenosylcobalamin biosynthesis; cob(II)yrinate a,c-diamide from sirohydrochlorin (anaerobic route): step 1/10. Porphyrin-containing compound metabolism; siroheme biosynthesis; siroheme from sirohydrochlorin: step 1/1. Desulfovibrio vulgaris possesses two versions of CbiK encoded within the genome, one cytoplasmic (CbiKC) and one periplasmic (CbiKP). Belongs to the CbiK family.