title: Mutational and phylogenetic analyses of the mycobacterial mbt gene cluster.
abstract: The mycobactin siderophore system is present in many Mycobacterium species, including M. tuberculosis and other clinically relevant mycobacteria. This siderophore system is believed to be utilized by both pathogenic and nonpathogenic mycobacteria for iron acquisition in both in vivo and ex vivo iron-limiting environments, respectively. Several M. tuberculosis genes located in a so-called mbt gene cluster have been predicted to be required for the biosynthesis of the core scaffold of mycobactin based on sequence analysis. A systematic and controlled mutational analysis probing the hypothesized essential nature of each of these genes for mycobactin production has been lacking. The degree of conservation of mbt gene cluster orthologs remains to be investigated as well. In this study, we sought to conclusively establish whether each of nine mbt genes was required for mycobactin production and to examine the conservation of gene clusters orthologous to the M. tuberculosis mbt gene cluster in other bacteria. We report a systematic mutational analysis of the mbt gene cluster ortholog found in Mycobacterium smegmatis. This mutational analysis demonstrates that eight of the nine mbt genes investigated are essential for mycobactin production. Our genome mining and phylogenetic analyses reveal the presence of orthologous mbt gene clusters in several bacterial species. These gene clusters display significant organizational differences originating from an intricate evolutionary path that might have included horizontal gene transfers. Altogether, the findings reported herein advance our understanding of the genetic requirements for the biosynthesis of an important mycobacterial secondary metabolite with relevance to virulence.
authors.affiliation: Department of Biology, Brooklyn College-City University of New York, Brooklyn, New York 112101, USA.
authors.forename: Sivagami Sundaram
authors.initials: SS
authors.lastname: Chavadi
authors.forename: Karen L
authors.initials: KL
authors.lastname: Stirrett
authors.forename: Uthamaphani R
authors.initials: UR
authors.lastname: Edupuganti
authors.forename: Olivia
authors.initials: O
authors.lastname: Vergnolle
authors.forename: Gigani
authors.initials: G
authors.lastname: Sadhanandan
authors.forename: Emily
authors.initials: E
authors.lastname: Marchiano
authors.forename: Che
authors.initials: C
authors.lastname: Martin
authors.forename: Wei-Gang
authors.initials: WG
authors.lastname: Qiu
authors.forename: Clifford E
authors.initials: CE
authors.lastname: Soll
authors.forename: Luis E N
authors.initials: LE
authors.lastname: Quadri
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics*; D053898:Biosynthetic Pathways / Q000235:genetics*; D017124:Conserved Sequence; D004252:DNA Mutational Analysis; D023061:Gene Order; D005810:Multigene Family; D020102:Mycobacterium smegmatis / Q000235:genetics*; D010080:Oxazoles / Q000378:metabolism*; D010802:Phylogeny
chemical_list: D001426:Bacterial Proteins; D010080:Oxazoles; C018608:mycobactins