EXTRACELLULAR AND SURFACE-EXPOSED POLYSACCHARIDES OF NONTUBERCULOUS MYCOBACTERIA

We studied the outermost constituents of the cell envelopes, which are involved in the interaction between the bacilli and the host cells, o f five pathogenic and non-pathogenic mycobacterial species for compari son with those we have previously characterized from M. tuberculosis. The extracellular materials (ECMs) were isolated by ethanol precipitat ion 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 mycobacter ia were clearly distinguishable. The first group comprised the pathoge nic species M. kansasii which produced large amounts of ECM, the glyco syl composition of which was similar to that of the SXM. The second gr oup comprised M. avium and the nonpathogenic strains of M. gastri, M. phlei and M. smegmatis which produced small amounts of ECM. This latte r group could be subdivided into those which produced carbohydrate-ric h ECM (M. avium and M. gastri) and those forming protein-rich ECM (M. phlei and M. smegmatis), a classification that correlated with the dif ference in the growth rate of the two subgroups. The glycosyl composit ion of the ECM of a given species was qualitatively similar to that of the SXM, except for M. avium and M. phlei whose SXM were devoid of ar abinose. In addition to glucose, mannose and arabinose, xylose was det ected in the hydrolysis products of the ECM and SXM of M. smegmatis, t he SXM of M. phlei and the ECM of some batches of M. avium. The polysa ccharide constituents of the ECM and SXM of the different mycobacteria were purified by anion-exchange and gel-filtration chromatography; al l were found to be neutral compounds devoid of acyl substituents. The extracellular polysaccharides consisted of high-molecular-mass glycoge n-like glucans, arabinomannans and mannans, structurally similar to th e corresponding substances previously characterized from the capsule o f M. tuberculosis. The same types of polysaccharides were characterize d from the SXM of all the strains, except M. avium and M. phlei which were devoid of arabinomannans. This study questions the unique and uni versal representation of the mycobacterial cell envelope and the exist ence of the so-called acidic polysaccharide-rich outer layer.