The diversity among 191 bacterial strains isolated from stem and root nodules (151 and 40 strains, respectively) of grown in different geographical areas in Senegal and in The Philippines was studied by using DNA-DNA hybridization techniques (S1 nuclease method), by determining DNA base compositions, by performing legume nodulation tests, and by determining nitrogenase activity. The following conclusions were drawn. (i) All of the strains produced stem and root nodules on . (ii) Most of the organisms (184 strains) belonged to the genus ; their guanine-plus-cytosine contents ranged from 66 to 68 mol%, they fixed N under free-living conditions, and they produced effective nodules on the stems and roots of . (iii) The seven other strains probably belonged to the genus , since guanine-plus-cytosine contents ranged from 59 to 63 mol% and they did not fix N under free-living conditions; three strains produced effective root nodules, but their stem nodules exhibited very low activity or were ineffective, and the four remaining strains produced ineffective nodules on both stems and roots. (iv) The genetic diversity among the 184 strains allowed us to divide them into two genomic species; genomic species 1 constituted the major group (175 strains) and corresponded to since all of the strains were more than 79% related to type strain ORS 571, and genomic species 2 contained nine strains that were only 44 to 53% related to type strain ORS 571 (difference between the denaturation temperatures of homologous and heterologous hybrids, more than 6°C) and more than 76% related to reference strains SD02 and SG28 (difference between the denaturation temperatures of homologous and heterologous hybrids, less than 3°C). The species that were distinct from cannot be named until they can be differentiated by phenotypic tests.


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