Separation of various Frankia strains in the Alnus and Elaeagnus host specificity groups using sugar analysis

Abstract

To confirm the role of glycosides in the taxonomy of Frankia, 79 strains initially isolated from Alnus spp., Myrica spp., Comptonia sp., Elaeagnus spp., Shepherdia spp., and Hippophaë sp. host plants were tested for relative sugar content after 2 and 8 weeks of growth. Gas chromatography was used to separate the trimethylsilyl derivatives of sugars present in whole-cell hydrolysates of the Frankia strains; six sugars were quantitatively analyzed including 2-O-methyl-D-mannose, a sugar ubiquitous in the genus Frankia. The separation of the Frankia strains into their appropriate host specificity group (Alnus or Elaeagnus), based only on the sugar content, was achieved using statistical analyses of observations at 2 and 8 weeks. All statistical analyses correlated together and showed a significant separation between both host specificity groups. 2-O-Methyl-D-mannose, the concentration of which varied greatly between the Alnus and Elaeagnus host specificity groups, was the most discriminant sugar. Moreover, it was constant at both ages. From discriminant analysis, the separation of the various Frankia strains tested into their respective host specificity group was more precise at 2 weeks with a classification success of 97%, as compared with 78% at 8 weeks. The Myrica gale isolates that nodulated host plants from both host specificity groups were generally intermediate in their sugar content between the Alnus and Elaeagnus host specificity groups.