- Volume 43, Issue 2, 1966

A collection of 267 strains, representing many of the principal biotypes among aerobic pseudomonads, has been subjected to detailed study, with particular emphasis on biochemical, physiological and nutritional characters. A total of 146 different organic compounds were tested for their ability to serve as sources of carbon and energy. Other characters that were studied included : production of extracellular hydrolases; nitrogen sources and growth factor requirements H-chemolithotrophy; denitrifying ability; pigment production; ability to accumulate poly-p-hydroxybutyrate as a cellular reserve material; biochemical mechanisms of aromatic ring cleavage; and nature of the aerobic electron transport system. The resultant data have revealed many hitherto unrecognized characters of taxonomic significance. As a consequence, it has become possible to recognize among the biotypes examined a limited number of species which can be readily and clearly distinguished from one another by multiple, unrelated phenotypic differences.

The base compositions of deoxyribonucleic acids extracted from aerobic pseudomonads were determined by examination of the buoyant density of each sample in caesium chloride (CsCl) gradients. A collection of 165 strains, representing many of the principal biotypes among aerobic pseudomonads, was subjected to this examination. The similarities and differences in the base compositions of the genetic material have been compared with the taxonomic arrangements suggested by the comparison of phenotypic (largely nutritional and enzymic) features. The data on base composition of the deoxyribonucleic acids of the various cultures support, for the greater part, the conclusions of Stanier, Palleroni & Doudoroff (1966) and of Redfearn, Palleroni & Stanier (1966). Data are also presented on pseudomonads not included in the latter studies.

A comparative study of many strains of Pseudom,onas pseudomallei and Bacillus mallei has shown that these two species are very similar with respect to their nutritional and biochemical properties, thus confirming earlier claims of a relationship between them, based on such criteria as pathological and serological properties. P. pseudomallei is in all respects a typical and nutritionally highly versatile member of the genus Pseudomonas. In view of this fact we propose that B. mallei should also be placed in the genus Pseudomonas, even though it is a permanently non-motile bacterium. The ecology and possible evolutionary relationships between the two species are discussed in the light of the present findings.