ИСТИНА

The study of chemical composition of bacterial cell envelope is of scientific and practical importance in many fields such as chemistry, biology, medicine, pharmacology, and environmental science. New data on cell wall glycopolymers in representatives of various bacterial taxa expand our notion on the diversity of natural polymers and biosynthetic potential of microorganisms. The results of comparative study of the cell wall glycopolymers in members of different species and higher taxa are of interest to microbial taxonomy. Over the years, we have been studying the structural diversity of the cell wall teichoic acids and other glycopolymers in representatives of Actinobacteria (orders Actinomycetales, Frankiales, Geodermatophilales, Kineosporiales, Micrococcales), with focus on seeking for new chemical structures of polymers and exploring the use of such polymers as chemotaxonomic markers for actinobacterial species. Here we summarize the results of studying teichoic acids from the taxonomic point of view in representatives of some genera, including Actinomadura, Agromyces, Brevibacterium, and Nocardiopsis. We also provide recent data on chemical composition and distribution of the phosphate-free glycopolymers in species of the order Micrococcales (genera Clavibacter, Curtobacterium, Promicromonospora, etc.) with special attention to various rhamnomannans and teichuronic acids revealed in members of the genus Rathayibacter (family Microbacteriaceae). The genus Rathayibacter currently comprises eight species with validly published names (R. rathayi, R. agropyri, R. caricis, R. festucae, R. iranicus, R. oskolensis, R. tritici, and R. toxicus). A few other species within this genus, including «Rathayibacter tanaceti» and «Rathayibacter acroptilonus», were revealed but have not been validly described. The species R. rathayi, R. iranicus, R. tritici, and R. toxicus are known to be plant pathogens which are transmitted to their host plants by seed gall nematodes of the genus Anguina. The Rathayibacter species exhibit high 16S rRNA gene sequence similarity (up to 99.7%) and are difficult to distinguish by conventional phenotypic properties. Species of the genus are also characterized by a similar set of cell wall sugars. All species contain mannose, rhamnose, and glucose; some include additionally galactose, xylose or fucose. We have shown that representatives of different Rathayibacter species (R. rathayi, R. festucae, R. iranicus, R. oskolensis, R. tritici, R. toxicus, «R. tanaceti», and «R. acroptilonus») possess the specific composition and chemical structures of the cell wall glycopolymers, and well distinguished from each other by this feature. All strains used in the work have structurally different rhamnormanns in their cell walls. The rhamnose and mannose residues in these polymers are linked by α-1→2 and / or α-1→3 glycosidic bonds in various combinations; some polymers have lateral branches (residues of mannose or xylose). Alongside rhamnomannans, most strains contain also teichuronic acids of different structures with monosaccharide constituents characteristic of particular Rathayibacter species. The teichuronic acids of some strains include additionally residues of pyruvic or lactic acid. It is worth noting that all glycopolymers identified in Rathayibacter spp. have been revealed in the cell wall of Gram-positives for the first time. Thus, the cell wall component, both teichoic acids and phosphate-free glycopolymers (as well as their combinations), can serve as chemotaxonomic markers of actinobacterial taxa at species and generic levels. All the above-stated evidence favors the advisability of further comparative studies of cell wall glycopolymers in actinobacteria and other Gram-positives. Of particular interest to taxonomy are the studies of polymers aiming at phenotypic characterization and differentiation of phylogenetically closely related species.