The organohalide-respiring bacterium Sulfurospirillum multivorans: a natural source for unusual cobamides.

Cobamides ('complete' corrinoids) are essential for organohalide-respiring bacteria because they act as cofactors of reductive dehalogenases (RDases). RDases are the key enzymes in organohalide respiration, a process relevant for environmental remediation. More than a decade ago, the unusual norpseudo-B12 was identified as cofactor of the tetrachloroethene RDase (PceA) purified from the epsilonproteobacterium Sulfurospirillum multivorans. Since then, the question was raised whether or not the production of the uncommon cobamide is a specific adaptation to the requirements of PceA. Recently, efforts were made to unravel variations in the cobamide biosynthetic pathway, which lead to the production of the structurally unique norpseudo-B12. The acquisition of genomic and proteomic data together with structural analyses of PceA provided insights into norcobamide formation and utilization. By the use of guided biosynthesis, S. multivorans was shown to be an effective cobamide producer capable of generating unusual norcobamides either functional or non-functional as cofactors of PceA. The organism turned out to be a suitable tool for testing the impact of cobamide structure on enzyme function. The results summarized here highlight S. multivorans in particular and the organohalide-respiring bacteria in general as a resource for new discoveries on cobamide diversity and utilization.