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One the cell surface of smooth of Yersinia enterocolitica 75 (Ye 75 S), and electron-lucent layer was identified in thin sections after incubation with Ye 75 S-antiserum. It is adjacent to the "double track" of the outer membrane. This layer does not appear on the analogously treated rough mutant (Ye 75 R), whose lipopolysaccharide (LPS) does not contain O-specific polysaccharides. It could be shown that this layer is formed by the O-specific side chains of LPS, which are unstained by routine methods. As the side chains of LPS obviosly make it difficult to visualize the LPS-strands in the outer membrane of rough strands was investigated. On Ye 75 R, the LPS-strands could be demonstrated only after treatment of cells with polymyxin B. After short time of exposure, the LPS appeared as contigous strand-like structures (diameter roughly 60 A) on the cell surface of cells which were negatively stained or dried by the critical-point-method. After prolonging polymyxin B treatment, "blebs" or "protrusions" appeared on the surface of Ye 75 cells, which were in negatively stained preparations and in thin sections identified as partly loosened LPS. The demonstration of LPS-strands in untreated cells was possible only on a "deep rough" mutant (Ye 161-45 a R), whose LPS contains only glucosamine and KDO besides lipid A. It is suggested that the LPS form a layer of contiguous strands (mid-to-distance 62 +/- 3 A) on the surface of negatively stained cells. According to this view, on the Ye 75 S, the O-specific side chains extend from this layer into the medium.

Phenol-water-extracted lipopolysaccharide (LPS) from Yersinia enterocolitica (strain 75 in smooth form; O-group I), after growth at 10 degrees C, contains approximately 40% (w/w) 6-deoxy-L-altrose. By increasing the cultivation temperature a significant decrease in the O-specific sugar is observed. LPS from cells grown at 40 degrees C contains about 12% 6-deoxy-L-altrose. Thin-section micrographs of cells grown at lower temperatures reveal a distinct layer corresponding to the O-specific side chains of LPS in contrast to cells grown at higher temperatures where a decrease in thickness is observed. It is assumed that this observation is due to the decreasing amount of the O-specific sugar at a higher cultivation temperature. The results obtained by the indirect immunoferritin test indicate that the O-specific polysaccharide layer covers the cell surface completely up to 37 degrees C. However, this layer no longer covers the entire surface of all cells as soon as an incubation temperature of 40 degrees C is applied.

A comparative study of various procedures of a lipopolysaccharide-protein complex (LPPC) from Yersinia pseudotuberculosis was carried out. The materials obtained were fractionated by molecular-sieve chromatography on Sepharose 2B resulting in highly aggregated complexes with antigen activity. LPPC aggregates dissociated in the presence of sodium dodecylsulphate (SDS) and urea. The chemical composition and serologic properties of fractions obtained are under consideration. The protein component of the complex consists of two major polypeptides (molecular weights--45,000 and 20,000) and some minor ones. The LPS component appeared to give 2--3 narrow bands in gel under conditions of SDS-polyacrylamide gel electrophoresis. It is suggested that such fractionation is caused by LPS association-dissociation in the course of electrophoresis.