The primary step of biotin synthesis in mycobacteria.

Abstract

Biotin plays an essential role in growth of mycobacteria. Synthesis of the cofactor is essential for <i>Mycobacterium tuberculosis</i> to establish and maintain chronic infections in a murine model of tuberculosis. Although the late steps of mycobacterial biotin synthesis, assembly of the heterocyclic rings, are thought to follow the canonical pathway, the mechanism of synthesis of the pimelic acid moiety that contributes most of the biotin carbon atoms is unknown. We report that the <i>Mycobacterium smegmatis</i> gene annotated as encoding Tam, an <i>O</i>-methyltransferase that monomethylates and detoxifies <i>trans</i>-aconitate, instead encodes a protein having the activity of BioC, an <i>O</i>-methyltransferase that methylates the free carboxyl of malonyl-ACP. The <i>M. smegmatis</i> Tam functionally replaced <i>Escherichia coli</i> BioC both in vivo and in vitro. Moreover, deletion of the <i>M. smegmatis tam</i> gene resulted in biotin auxotrophy, and addition of biotin to <i>M. smegmatis</i> cultures repressed <i>tam</i> gene transcription. Although its pathogenicity precluded in vivo studies, the <i>M. tuberculosis</i> Tam also replaced <i>E. coli</i> BioC both in vivo and in vitro and complemented biotin-independent growth of the <i>M. smegmatis tam</i> deletion mutant strain. Based on these data, we propose that the highly conserved mycobacteria<i>l tam</i> genes be renamed <i>bioC</i><i>M. tuberculosis</i> BioC presents a target for antituberculosis drugs which thus far have been directed at late reactions in the pathway with some success.