Two distinct roles for two functional cobaltochelatases (CbiK) in Desulfovibrio vulgaris Hildenborough

The sulfate-reducing bacterium Desulfovibrio vulgaris Hildenborough possesses a large number of porphyrin-containing proteins whose biosynthesis is poorly characterized. In this work, we have studied two putative CbiK cobaltochelatases present in the genome of D. vulgaris. The assays revealed that both enzymes insert cobalt and iron into sirohydrochlorin, with specific activities with iron lower than that measured with cobalt. Nevertheless, the two D. vulgaris chelatases complement an E. coli cysG mutant strain showing that, in vivo, they are able to load iron into sirohydrochlorin. The results showed that the functional cobaltochelatases have distinct roles with one, CbiK(C), likely to be the enzyme associated with cytoplasmic cobalamin biosynthesis, while the other, CbiK(P), is periplasmic located and possibly associated with an iron transport system. Finally, the ability of D. vulgaris to produce vitamin B-12 was also demonstrated in this work.