A vitamin B 12 transporter in Mycobacterium tuberculosis

Abstract

Vitamin B 12 -dependent enzymes function in core biochemical pathways in Mycobacterium tuberculosis , an obligate pathogen whose metabolism in vivo is poorly understood. Although M. tuberculosis can access vitamin B 12 in vitro , it is uncertain whether the organism is able to scavenge B 12 during host infection. This question is crucial to predictions of metabolic function, but its resolution is complicated by the absence in the M. tuberculosis genome of a direct homologue of BtuFCD, the only bacterial B 12 transport system described to date. We applied genome-wide transposon mutagenesis to identify M. tuberculosis mutants defective in their ability to use exogenous B 12 . A small proportion of these mapped to Rv1314c , identifying the putative PduO-type ATP : co(I)rrinoid adenosyltransferase as essential for B 12 assimilation. Most notably, however, insertions in Rv1819c dominated the mutant pool, revealing an unexpected function in B 12 acquisition for an ATP-binding cassette (ABC)-type protein previously investigated as the mycobacterial BacA homologue. Moreover, targeted deletion of Rv1819c eliminated the ability of M. tuberculosis to transport B 12 and related corrinoids in vitro . Our results establish an alternative to the canonical BtuCD-type system for B 12 uptake in M. tuberculosis , and elucidate a role in B 12 metabolism for an ABC protein implicated in chronic mycobacterial infection.