Extracellular and surface-exposed polysaccharides of non-tuberculous mycobacteria

Abstract

We studied the outermost constituents of the cell envelopes, which are involved in the interaction between the bacilli and the host cells, of five pathogenic and non-pathogenic mycobacterial species for comparison with those we have previously characterized from M. tuberculosis. The extracellular materials (ECMs) were isolated by ethanol precipitation and compared to the surface-exposed materials (SXMs) extracted by mechanical means. The materials from both sources were composed almost exclusively of polysaccharides and proteins. Two groups of mycobacteria were clearly distinguishable. The first group comprised the pathogenic species M. kansasii which produced large amounts of ECM, the glycosyl composition of which was similar to that of the SXM. The second group comprised M. avium and the nonpathogenic strains of M. gastri, M. phlei and M. smegmatis which produced small amounts of ECM. This latter group could be subdivided into those which produced carbohydrate-rich ECM (M. avium and M. gastrr') and those forming protein-rich ECM (M. phlei and M. smegmatis), a classification that correlated with the difference in the growth rate of the two subgroups. The glycosyl composition of the ECM of a given species was qualitatively similar to that of the SXM, except for M. avium and M. phlei whose S X M were devoid of arabinose. In addition to glucose, mannose and arabinose, xylose was detected in the hydrolysis products of the ECM and SXM of M. smegmatis, the SXM of M. phlei and the ECM of some batches of M. avium. The polysaccharide constituents of the ECM and S X M of the different mycobacteria were purified by anion-exchange and gel-filtration chromatography; all were found to be neutral compounds devoid of acyl substituents. The extracellular polysaccharides consisted of high-molecular-mass glycogen-like glucans, arabinomannans and mannans, structurally similar to the corresponding substances previously characterized from the capsule of M. tuberculosis. The same types of polysaccharides were characterized from the S X M of all the strains, except M. avium and M. phlei which were devoid of arabinomannans. This study questions the unique and universal representation of the mycobacterial cell envelope and the existence of the so-called acidic polysaccharide-rich outer layer.i

The impact of the absence of glycopeptidolipids on the ultrastructure, cell surface and cell wall properties, and phagocytosis of Mycobacterium smegmatis

“…To compare the amounts of materials released into the culture fluids, the two strains were grown in synthetic Sauton's medium. Similar amounts of carbohydrate and protein were found in the culture fluids of the two strains which exhibited the same sugar composition (data not shown) that was similar to that previously found for M. smegmatis (Lemassu et al, 1996). Thus, the absence of GPLs from the mutant strain does not induce the release of surface components into the culture fluid.…”

“…Surface-exposed material (SEM) and extracellular compounds were extracted and analysed as previously described (Lemassu et al, 1996 ;OrtaloMagne! et al 1996).…”

“…The carbohydrate and protein contents of the SEMs from the two strains were comparable. The percentages of carbohydrate in the SEMs of the parent and the mutant strains were estimated to 13n2 % and 13n8 % of the dry weight, respectively ; the sugar compositions of the SEMs from both origins were similar and consisted of arabinose, mannose, xylose and glucose (Lemassu et al, 1996). Protein represented 59n3 % and 75n4 % of the dry weight of the SEMs of the parent and mutant strains, respectively.…”

“…Protein represented 59n3 % and 75n4 % of the dry weight of the SEMs of the parent and mutant strains, respectively. Surface lipids represent a very minor fraction (0n02-0n1 % bacterial dry weight) of mycobacteria grown on synthetic Sauton's medium (Lemassu et al, 1996 ;Ortalo-Magne! et al, 1996).…”

Surface-exposed Glycopeptidolipids of Mycobacterium smegmatis Specifically Inhibit the Phagocytosis of Mycobacteria by Human Macrophages

“…Some of its components have been implicated in the interaction with macrophages (17). The major carbohydrate constituent of the capsule, a glycogen-like glucan (14), has been shown to inhibit the binding of M. tuberculosis to complement receptor type 3-expressing Chinese hamster ovary cells (18). The purified mannose-capped lipoarabinomannan (Man-LAM), a cell envelope-associated glycoconjugate, interacts with the mannose receptor of macrophages (19).…”