Sulfolipid Deficiency Does Not Affect the Virulence ofMycobacterium tuberculosisH37Rv in Mice and Guinea Pigs

Abstract

Lipids that are found only in the cell envelope of pathogenic mycobacteria, such as those containing multiple methyl-branched fatty acids, have long been thought to play a role in pathogenesis. Among these complex lipids, sulfolipids have been the most extensively studied over the last 50 years. The numerous biological effects exhibited by purified sulfolipids on phagocytic cells led to the idea that these molecules are probably important virulence factors facilitating the intracellular survival of Mycobacterium tuberculosis. However, definitive evidence to support this concept has been lacking. The recent construction of an isogenic sulfolipid-deficient mutant of M. tuberculosis H37Rv (Sirakova et al., J. Biol. Chem. 276:16833-16839, 2001) has for the first time provided the opportunity to directly assess the contribution of these complex lipids to pathogenesis. In the present study, we show that against all expectations, sulfolipid deficiency does not significantly affect the replication, persistence, and pathogenicity of M. tuberculosis H37Rv in mice and guinea pigs or in cultured macrophages.Tuberculosis remains a major health problem worldwide (26). Mycobacterium tuberculosis, the causative agent of this disease in humans, has the capacity to infect, replicate in, and persist inside host macrophages. The virulence factors enabling M. tuberculosis to escape the bactericidal mechanisms of these cells, notably by blocking phagosome-lysosome fusion, are essentially unknown (6). A study conducted some 55 years ago by Middlebrook and collaborators (21) recognized that the curious ability of the tubercle bacillus to grow in culture as serpentine cords was relatively restricted to virulent strains. Dubos and Middlebrook (7) also observed that the virulent cord-forming strains invariably absorbed the cationic dye neutral red, while most attenuated strains of M. tuberculosis and saprophytic mycobacteria did not.In a search for the component of virulent mycobacteria that induced uptake of the dye, Middlebrook and coworkers (20) isolated sulfolipids. This family of molecules is composed of sulfated trehalose esters acylated with three to four acyl groups consisting of one short saturated fatty acid (palmitic acid or stearic acid) and different combinations of long-chain multiple methyl-branched fatty acids (the phthioceranic and hydroxyphthioceranic acids) (for a review, see references 9 and 11). Consistent with their suspected role in virulence, sulfolipids are found only in the human pathogen M. tuberculosis (9). Interestingly, sulfolipids are present in the virulent laboratory strain M. tuberculosis H37Rv but absent from the avirulent strain M. tuberculosis H37Ra (20).

Phosphorylation of PhoP Protein Plays Direct Regulatory Role in Lipid Biosynthesis of Mycobacterium tuberculosis

“…These reports coupled with recent studies show that among the reasons for the attenuation of M. tuberculosis the H37Ra strain is a single nucleotide polymorphism within the phoP gene that (a) is incapable of restoring polyketide-derived acyltrehalose synthesis in a phoP-phoR knock-out mutant of H37Rv (19) and (b) inhibits secretion of proteins that are important for virulence (18). Although these results establish a strong link between PhoP with lipid biosynthesis and virulence regulation, studies using a pks2-3/4 knockout mutant of M. tuberculosis H37Rv clearly show that not polyketide-derived acyltrehaloses but rather phthiocerol dimycocerosates, which are not regulated by PhoP, are the major contributor of virulence of the tubercle bacillus (19,43,44). However, it should be noted that proteins encoded by genes of the pks2 cluster (Rv3825c-3824c-3823c) and msl3 cluster (Rv1180-Rv1182-Rv1183) (supplemental Fig.…”

Bacterial immunostat: Mycobacterium tuberculosis lipids and their role in the host immune response

“…SL-1 also directly inhibits macrophage priming, which results in reduced superoxide anion (O 2 -) release, reduced phagocytosis, and reduced release of IL-1 75 , and affects neutrophil signal transduction pathways 76 . Nevertheless, the role of SL-1 in the virulence of M. tuberculosis remains questionable 77 . Kato and Goren 78 showed that SL-1 damages the mitochondrial structure in synergy with TDM, but no toxic effect was noted in mice injected intraperitoneally with SL-1 alone.…”

PapA1 and PapA2 are acyltransferases essential for the biosynthesis of theMycobacterium tuberculosisvirulence factor Sulfolipid-1

“…Intriguingly, the ⌬mmpL8 mutant, which lacks SL-1 but accumulates SL 1278 , shows attenuated virulence in mice (23,24). By contrast, a ⌬pks2 mutant, which lacks both SL-1 and SL 1278 , is indistinguishable from WT M. tb in mice and guinea pigs (23,26). These observations suggest that SL 1278 , and possibly other SL-1 intermediates, modulate M. tb pathogenesis.…”