- Volume 133, Issue 9, 1987

SUMMARY: Resistance of Rhizobium loti strain NZP2037 to the prodelphinidin-rich flavolan (condensed tannin) present in the roots of Lotus pedunculatus was associated with the presence of a peptidoglycan-bound flavolan-binding polysaccharide (FBP) in the outer cell membrane of this bacterium. The outer cell membrane of a flavolan-sensitive strain, NZP2213, did not contain this polysaccharide. FBP was extractable in highest concentration from NZP2037 cells during exponential growth of the bacteria. This correlated with exponential-phase cells of NZP2037 showing maximum resistance to flavolan. When added to cultures of NZP2213, FBP afforded a concentration-dependent protection of this strain to the bactericidal effect of the flavolan. ELISA and immunogold labelling of Rhizobium cells using FBP-specific antibodies confirmed the presence of FBP on the outer cell surface of NZP2037 cells and its absence from NZP2213 cells. Co-inoculation of L. pedunculatus with antibiotic-resistant mutants of NZP2037 and NZP2213 resulted in the formation of N2-fixing nodules containing both strains.

SUMMARY: The phylogenetic incoherency of the genus Bacillus as presently described is demonstrated by analysis of both published and new data from comparative 16S rRNA cataloguing of nine Bacillus species and a number of related non-Bacillus taxa, i.e. Caryophanon latum, Filibacter limicola and Planococcus citreus. While the ellipsoidal-spore-forming bacilli, e.g. B. subtilis and allied species, formed a coherent cluster, the round-spore-forming bacilli showed a higher degree of relationship to the non-spore-forming organisms than these bacilli show among each other. Thus B. sphaericus clustered with C. latum, B. globisporus grouped with F. limicola, B. pasteurii with Sporosarcina ureae, and ‘B. aminovorans’ with P. citreus, respectively. These organisms formed two related subclusters which, in their phylogenetic depth, are comparable to that of the B. subtilis subline. With the exception of ‘B. aminovorans’ the 16S rRNA phylogeny was entirely consistent with the distribution of murein types. Even more distantly related to and grouping outside the main Bacillus cluster was B. stearothermophilus, which displayed a moderate relationship to Thermoactinomyces vulgaris. Taxonomic problems arising from the new insights into the intrageneric relationships of Bacillus are discussed.