The salicylate-derived mycobactin siderophores of Mycobacterium tuberculosis are essential for growth in macrophages

Abstract

Mycobacterium tuberculosis is an important pathogen of mammals that relies on 2-hydroxyphenyloxazoline-containing siderophore molecules called mycobactins for the acquisition of iron in the restrictive environment of the mammalian macrophage. These compounds have been proposed to be biosynthesized through the action of a cluster of genes that include both nonribosomal peptide synthase and polyketide synthase components. One of these genes encodes a protein, MbtB, that putatively couples activated salicylic acid with serine or threonine and then cyclizes this precursor to the phenyloxazoline ring system. We have used gene replacement through homologous recombination to delete the mbtB gene and replace this with a hygromycin-resistance cassette in the virulent strain of M. tuberculosis H37Rv. The resulting mutant is restricted for growth in iron-limited media but grows normally in ironreplete media. Analysis of siderophore production by this organism revealed that the biosynthesis of all salicylate-derived siderophores was interrupted. The mutant was found to be impaired for growth in macrophage-like THP-1 cells, suggesting that siderophore production is required for virulence of M. tuberculosis. These results provide conclusive evidence linking this genetic locus to siderophore production.

LspA inactivation in Mycobacterium tuberculosis results in attenuation without affecting phagosome maturation arrest

“…This suggests that LspA is required for multiplication of M. tuberculosis in early phagosomes. The early phagosome is thought to be a nutrient-restricted environment, which is important in limiting the availability of nutients to phagocytosed bacteria (De Voss et al, 2000;Wagner et al, 2005). Despite some research in this field the key elements critical for adaptation of mycobacteria to this prelysosomal environment are unknown.…”

Alternative activation deprives macrophages of a coordinated defense program to Mycobacterium tuberculosis

“…Mycobactin is an intracellular bacterial siderophore which plays a critical role in iron acquisition and transport in M. tuberculosis [50]. To monitor the status of iron starvation of M. tuberculosis within alternatively activated macrophages, expression levels of marker transcripts encoding proteins involved in mycobactin synthesis (mbtB, Rv2383c; mbtJ, Rv2385; mbtI, Rv2386c) as well as the iron storage protein bacterioferritin (bfrB, Rv3841) were determined by qPCR.…”

Mycobacterium tuberculosis acquires iron by cell-surface sequestration and internalization of human holo-transferrin

“…In addition, this pathogen also acquires iron from haem 4 ; intracellular M.tb are known to actively recruit host iron carrier proteins transferrin and lactoferrin to the phagosomal compartment [5][6][7][8] . It is reported that carboxymycobactins remove iron from transferrin in the phagosome, while mycobactins present in the bacterial membrane transport this iron into the bacterial cytoplasm 9,10 . Carboxymycobactin also delivers iron by a mycobactinindependent mechanism using the IrtAB transporter 11 .…”