To gain insight into the pathogenesis of tuberculosis, a molecular definition of the tubercle bacillus cell envelope, which is involved in the early stages of the infection, is required. The cell-surface-exposed material of the pathogen was isolated by mechanical means and chemically analysed. It was shown by scanning electron microscopy that the method used for extracting the surfacecovering material preserves the integrity of the bacilli. Surprisingly, in view of the current opinion, only small amounts of lipids ( 1 4 % ) were present. Polysaccharides and proteins were the main components of the material. The polysaccharides were neutral and lipid-free D-glucan, D-arabino-D-mannan and D-mannan, which were eluted from gel-filtration columns in positions corresponding to molecular masses of 120,13 and 4 kDa, respectively. Based on NMR spectroscopy and conventional chemical analyses, the major structural motifs of the purified polysaccharides were established as being identical to those of the polysaccharides we previously isolated from the culture filtrate of the tubercle bacillus. lmmunocytochemical studies showed that these compounds were not only surface-located but were also present in the inner capsular compartment. The major protein constituents exhibited the same mobilities on SDS-PAGE as those of the culture filtrate of the tubercle bacillus and readily reacted with the monoclonal antibodies directed against these molecules. These proteins included the 19 and 38 kDa lipoproteins, the 30/31 kDa fibronectin-binding proteins and the 40 kDa L-alanine dehydrogenase. These findings suggest that the culture filtrate material represents part of the capsule which, in an in wivo context, could contribute to the electron transparent zone surrounding the tubercle bacillus. The 24 kDa (MPBTT64) protein was found to be a secreted protein, as it was detected almost exclusively in the culture filtrate. Taken together, the data give a new insight into the surface-exposed compounds of the tubercle bacillus and may explain part of the nature and limitation of the host immunity towards the pathogen.

Glycopeptidolipids (GPLs) are a class of species-or type-specific mycobacterial lipids and major constituents of the cell envelopes of many non-tuberculous mycobacteria. To determine the function of GPLs in the physiology of these bacteria, a mutant of Mycobacterium smegmatis in which the gene encoding a mycobacterial nonribosomal peptide synthetase has been inactivated by transposon mutagenesis was analysed. Labelling experiments indicated that half of the bacterial GPLs were located on the cell surface and represented 85 % of the surface-exposed lipids of the parent strain whereas the mutant was defective in the production of the GPLs. Compared to the parent smooth morphotype strain, the GPL-deficient mutant strain exhibited a rough colony morphology, an increase of the cell hydrophobicity and formed huge aggregates. As a consequence, the mutant cells were no longer able to bind ruthenium red, as observed by transmission electron microscopy. The altered surface properties of the mutant cells also affected the phagocytosis of individual bacilli by human monocyte-derived macrophages since mutant cells were internalized more rapidly than cells from the parent strain. Nevertheless, no specific release of surface constituents into the culture broth of the mutant was observed, indicating that the cell surface is composed of substances other than GPLs and that these are essential for maintaining the architecture of the outermost layer of the cell envelope. Importantly, the absence of these major extractable lipids of M. smegmatis from the mutant strain has a profound effect on the uptake of the hydrophobic chenodeoxycholate by cells, indicating that GPLs are involved in the cell wall permeability barrier of M. smegmatis. Altogether, these data showed that, in addition to being distinctive markers of numerous mycobacterial species, GPLs play a role in the bacterial phenotype, surface properties and cell wall permeability.

Infection by Shigella flexneri is characterized by infiltration of neutrophils in the intestinal mucosa and by a strong inflammatory reaction. Although neutrophils are constitutively programmed to die by apoptosis, we show that isolated human neutrophils undergo necrosis 2 h after infection with virulent S. flexneri strain M90T but not with the virulence plasmid-cured strain BS176. This was demonstrated by the release of azurophil granule proteins concomitant with the release of lactate dehydrogenase (LDH), disruption of the plasma membrane, and absence of DNA fragmentation. Mutants with the mxiD1 gene, coding for an essential component of the secretion type III machinery, or the genes coding for IpaB or IpaC invasins deleted were not cytotoxic. Neutrophil necrosis occurred independently of the bacterial ability to leave phagosomes, and it involved actin polymerization, as the addition of cytochalasin D after phagocytosis of Shigella inhibited the release of LDH. In conclusion, Shigella kills neutrophils by necrosis, a process characterized by the release of tissue-injurious granular proteins. This probably contributes to disruption of the epithelial barrier, leading to the dysentery observed in shigellosis and allowing Shigella to enter its host cells.

Mutations in genes encoding components of the intraflagellar transport (IFT) complexes have previously been associated with a spectrum of diseases collectively termed ciliopathies. Ciliopathies relate to defects in the formation or function of the cilium, a sensory or motile organelle present on the surface of most cell types. IFT52 is a key component of the IFT-B complex and ensures the interaction of the two subcomplexes, IFT-B1 and IFT-B2. Here, we report novel IFT52 biallelic mutations in cases with a short-rib thoracic dysplasia (SRTD) or a congenital anomaly of kidney and urinary tract (CAKUT). Combining in vitro and in vivo studies in zebrafish, we showed that SRTD-associated missense mutation impairs IFT-B complex assembly and IFT-B2 ciliary localization, resulting in decreased cilia length. In comparison, CAKUT-associated missense mutation has a mild pathogenicity, thus explaining the lack of skeletal defects in CAKUT case. In parallel, we demonstrated that the previously reported homozygous nonsense IFT52 mutation associated with Sensenbrenner syndrome [Girisha et al. (2016) A homozygous nonsense variant in IFT52 is associated with a human skeletal ciliopathy. Clin. Genet., 90, 536–539] leads to exon skipping and results in a partially functional protein. Finally, our work uncovered a novel role for IFT52 in microtubule network regulation. We showed that IFT52 interacts and partially co-localized with centrin at the distal end of centrioles where it is involved in its recruitment and/or maintenance. Alteration of this function likely contributes to centriole splitting observed in Ift52−/− cells. Altogether, our findings allow a better comprehensive genotype–phenotype correlation among IFT52-related cases and revealed a novel, extra-ciliary role for IFT52, i.e. disruption may contribute to pathophysiological mechanisms.