Deoxyribonucleic acid similarity experiments in which the S1 nuclease methodology was used were performed on strains of Pseudornonas species, including some that had not been previously subjected to similarity measurements. The results obtained with this technique confirmed and expanded previous observations on the low levels of deoxyribonucleic acid similarity among species of the genus as determined by membrane competition experiments. A general discussion of the results and nomenclatural status of some of the species is included.The genus Pseudornonas has been subdivided into five groups on the basis of ribosomal ribonucleic acid (rRNA)-deoxyribonucleic acid (DNA) hybridization experiments (23,24,27). This classification has received ample confirmation from work done in various laboratories in which a number of different experimental approaches have been used. In the years since it was first proposed, no significant changes have been required, with the exception of assignment of organisms to some of the groups of some Pseudomonas species that were not included in the original studies. Thus, in the recent rRNA-DNA hybridization study of Byng et al. (3), Pseudomonas panici, Pseudomonas synxantha, Pseudomonus angulata, and Pseiidomonas frugi were found to belong to group I; Pseudomonas pyrrocinia and Pseudomonas andropogorzis were found to belong to group 11; and Pseudomonas geniculata was found to belong to group V. In addition, Alcaligenes paradoxus was found to be related to organisms belonging to group 11, and Alcaligenes eutrophus was found to be related to group 111 organisms.The homogeneity within each Pseudomonas rRNA similarity cluster is very high, with most species having nearly 100% rRNA similarity (3, 27), although the levels of DNA similarity between species within each rRNA cluster are low (25). In contrast, we have not always found this clear clustering among groups of anaerobic bacteria (16)(17)(18). In order to confirm this rather interesting observation on the Pseudomonas groups and to extend DNA similarity measurements between additional species of the genus, the experiments described here were performed. In addition, some of the species were not included on the 1980 Approved Lists of Bacterial Names (33), and others appear to be synonyms. Nomenclatural proposals concerning some of these organisms are included below.
MATERIALS AND METHODSBacterial strains. The organisms used in this study were the same as those used in a previous rRNA similarity study (3). All were obtained from the American Type Culture Collection, Rockville, Md.DNA preparation. The organisms were grown in a medium containing 1% tryptone (BBL Microbiology Systems, Cockeysville, Md.), 0.5% yeast extract (Difco Laboratories, Detroit, Mich.), and 0.5% glucose. Erlenmeyer flasks (volume, 2 liters) containing 500 ml of medium were inoculated with 5-ml portions of broth cultures and shaken overnight at 250 rpm on a rotary shaker at 30°C. The harvested cells were suspended in a 0.15 M NaCl-0.01 M ethylenediaminetetraacetic acid sal...