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Isolation and characterization of 14 additional genes specifying the anaerobic biosynthesis of cobalamin (vitamin B₁₂) in Propionibacterium freudenreichii (P. shermanii)

Center for Biological NMR, Department of Chemistry, Texas A&M University, College Station, TX 77843-3255, USA¹
School of Biological Sciences, Queen Mary, University of London, Mile End Road, London E1 4NS, UK²

Author for correspondence: Charles A. Roessner. Tel: +1 979 845 3243. Fax: +1 979 845 5992. e-mail: c-roessner{at}tamu.edu

A search for genes encoding enzymes involved in cobalamin (vitamin B₁₂) production in the commercially important organism Propionibacterium freudenreichii (P. shermanii) has resulted in the isolation of an additional 14 genes encoding enzymes responsible for 17 steps of the anaerobic B₁₂ pathway in this organism. All of the genes believed to be necessary for the biosynthesis of adenosylcobinamide from uroporphyrinogen III have now been isolated except two (cbiA and an as yet unidentified gene encoding cobalt reductase). Most of the genes are contained in two divergent operons, one of which, in turn, is closely linked to the operon encoding the B₁₂-dependent enzyme methylmalonyl-CoA mutase. The close linkage of the three genes encoding the subunits of transcarboxylase to the hemYHBXRL gene cluster is reported. The functions of the P. freudenreichii B₁₂ pathway genes are discussed, and a mechanism for the regulation of cobalamin and propionic acid production by oxygen in this organism is proposed.

Keywords: hem operon, methylmalonyl-CoA mutase, transcarboxylase, metabolic regulation, genetic linkage

The GenBank accession numbers for the sequences reported in this paper are AY033235, AY033236, U13043 and U51164.

^a Present address: Protein Engineering, Iogen Corp., 400 Hunt Club Road, Ontario, Ottawa, Canada K1V 1C1.

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