C-labeled ribosomal ribonucleic acids (rRNAs) were prepared from NZP 5549(T = type strain) and DSM 130, and [H]rRNAs were prepared from NZP 4009 and NZP 2037. Labeled rRNA from ICPB TT111 (a member of cluster 2) was also used. These rRNAs were hybridized under optimal conditions with filter-fixed deoxyribonucleic acids (DNAs) from 24 strains of rhizobia representing nine previously identified DNA-DNA homology groups and with DNAs from various other organisms. Each hybrid was described by the following two parameters: the temperature at which 50% of the hybrid was denatured () and percentage of rRNA binding. From rRNA similarity maps and a dendrogram the following conclusions were drawn. (i) There are at least three genetically distinct groups in the present genus Group I includes , and Group II is represented by , and group III includes rhizobia isolated from and (goatsrue.). (ii) The rRNA cistrons of group I strains resemble those of cluster 2 strains. (iii) The rRNA cistrons of resemble those of more closely than the rRNA cistrons of or cluster 2 do. (iv) The rRNA cistrons of resemble the rRNA cistrons of less than the rRNA cistrons of strains belonging to either cluster 1 or cluster 2. (v) The rRNA cistrons of rhizobia resemble the rRNA cistrons of about as much as the rRNA cistrons of cluster 1 and resemble the rRNA cistrons of less. (vi) The rRNA cistrons of and resemble one another much less than do the rRNA cistrons of and other genera presently included in the family and ). (vii) strains belonging to four DNA-DNA homology groups all contain rRNA cistrons which closely resembled the rRNA cistrons of NZP 5549. (viii) contains rRNA cistrons which have diverged from the rRNA cistrons of to about the same extent as the rRNA cistrons of group I and ; on this basis we suggest that the photosynthetic ancestor of may have been a rhodopseudomonad and that a phylogenetic classification should group these genera together. (ix) Stemnodulating strain ORS 571, from belongs to the rRNA branch; it is quite distinct from and Two representative strains which nodulate roots belong in the group containing the fast-growing rhizobia.


Article metrics loading...

Loading full text...

Full text loading...


Most cited this month Most Cited RSS feed

This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error