Colwell, R. R. (University of Washington, Seattle), and J. Liston. Taxonomic relationships among the pseudomonads. J. Bacteriol. 82:1-14. 1961.-An electronic computer technique, utilizing the Adansonian principle that every feature should have equal weight, was applied in an effort to derive a taxonomy of the Pseudomonas-Achromobacter group of gram-negative, asporogenous, rodlike bacteria. The validity of the general method was tested by an analysis of 40 well defined strains, principally derived from type culture collections and representative of different genera and families of the Pseudomonadales and the Eubacteriales. The analysis clearly separated groups which are recognized to be taxonomically distinct. Aerogenic Aeromonas were most similar to the Enterobacteriaceae and taxonomically distinct from the anaerogenic Aeromonas formicans which was more similar to the Pseudomonas group. Oxidative Vibrio species grouped with Pseudomonas and probably should be renamed Pseudomonas. Fermentative Vibrio species showed affinities with A. formicans.Fifty-four Pseudomonas strains out of 58 tested in an analysis of 80 bacterial cultures, clustered into four large groups: group 1, a marine group within which appeared a psychrophilic, nonproteolytic species subgroup related to Vibrio beijerinckii and a subgeneric subgroup which included Pseudomonas elongata; group 2, a subgeneric mesophilic group including Vibrio percolans and associated with Pseudomonas fragi; group 3, a fluorescent pigment-producing group, including three subgroups, a psychrophilic aeruginosa-like species group, a mesophilic Pseudomonas aeruginosa species group, and a heterogeneous subgeneric group containing Vibrio cuneatus and related to Pseudomonas fluorescens and Pseudomonas pavonacea; group 4, a subgeneric nonpigment-producing, mesophilic group, which included Vibrio tyrogenus, Pseudomonas ovalis, and Pseudomonas denitrificans.