Chelates cobalt to the cobalamin precursor as part of the anaerobic pathway to cobalamin biosynthesis. Co-sirohydrochlorin + 2 H(+) = Co(2+) + sirohydrochlorin Binds 1 [4Fe-4S] cluster per dimer. Cofactor biosynthesis; adenosylcobalamin biosynthesis; cob(II)yrinate a,c-diamide from sirohydrochlorin (anaerobic route): step 1/10. Homodimer. Belongs to the CbiX family. CbiXL subfamily.