- Volume 88, Issue 2, 1975

SUMMARY: rRNA homologies have been determined on reference strains representing 56 species of Clostridium. Competition experiments using tritium-labelled 23 S rRNA were employed. The majority of the species had DNA with 27 to 28% guanine plus cytosine (% GC). These fell into rRNA homology groups I and II, which were well defined, and a third group which consisted of species which did not belong in groups I and II. Species whose DNA was 41 to 45% GC comprised a fourth group. Thirty species were placed into rRNA homology group I on the basis of having 50% or greater homology with Clostridium butyricum, C. perfringens, C. carnis, C. sporogenes, C. novyi or C. pasteurianum. Ten subgroups were delineated in homology group I. Species in each subgroup either had high homology with a particular reference species or a similar pattern of homologies to all of the reference organisms. The eleven species in rRNA homology group II had 69% or greater homology to C. lituseburense. Species in groups I and II had intergroup homologies of 20 to 40%. The six species in group III had very low homologies with groups I and II. Negligible homology also resulted when five of the species were tested against the sixth, C. ramosum. The five species having DNA with 41 to 45% GC were C. innocuum, C. sphenoides, C. indolis, C. barkeri and C. oroticum. Little rRNA homology was apparent between C. innocuum and the other high % GC species or with several Bacillus species having similar % GC DNA. Correlations between homology results and phenotypic characteristics are discussed.

SUMMARY: Two strains of heterotrophic, non-motile, Gram-negative extreme thermophiles have been isolated from hot tap water. These strains (NH and DI) have been characterized and compared with strains of the genus Thermus. Few of the single organic compounds tested supported growth in the presence of ammonium salts, and, like Thermus strains, growth on undefined media was restricted to dilute tryptone-yeast extract-mineral salt solutions. Nutrient agar and similar common laboratory media did not support growth. The growth rate was similar to that of Thermus strains, as was the unusual pattern of antibiotic resistance. Mean base composition of NH was 61·4% guanine plus cytosine (G + C), and of DI was 62·0 to 62·2% G + C, which are several per cent lower than the G + C contents of other strains so far described.

SUMMARY: Selected isolates of Sclerotinia sclerotiorum (Lib.) de Bary were grown together on agar, and the mycelial reactions in the regions of association studied. Three types of reaction were observed: (i) free intermingling of mycelia without antagonism and with occasional hyphal anastomoses; (ii) a white, later pigmented, incompatibility zone associated with excessive branching of hyphal tips at the margins of one or both of the colonies; (iii) a brown incompatibility zone of variable intensity, accompanied by early lysis of the tips of the peripheral hyphae of one of the colonies. Associated with reaction types (ii) and (iii) were interactions in which the hyphae of one isolate attached themselves to and grew around those of another isolate; this resulted in the lysis of the ‘attacked’ hyphae. The grouping of the selected isolates by means of reaction types and ‘predatory’ interactions gives support for the separation of S. sclerotiorum into three distinct species, S. minor, S. trifoliorum and S. sclerotiorum.