Three bacterial isolates, a Pseudomonas sp., a Bacillus sp., and an Arthrobacter sp., commonly isolated from a hummocky sedge-moss meadow at Devon Island, N.W.T., Canada, were selected for further taxonomic characterization and for a study of the effects of temperature and limiting carbon source on growth. Pseudomonas M216 resembled P. putida and Bacillus M153, B. carotarum. Arthrobacter M51 had growth-factor requirements which were more complex than those of any named species of that genus. The temperature ranges of growth indicated that Pseudomonas M216 and Arthrobacter M51 were psychrotrophic while Bacillus M153 was mesophilic. Growth in batch culture at limiting glucose concentrations enabled the calculation of Ks and Y values for each isolate. These were similar to those obtained for other organisms and Pseudomonas M216 and Bacillus M153 showed a high affinity for glucose. The nutritional versatility of Arthrobacter M51 and its ability to grow at low temperatures and the high growth rates and affinity of Pseudomonas M216 for low substrate concentrations may account for their competitive abilities in the natural environment, while the inability of Bacillus M153 to grow at low temperatures may limit its activity in tundra soils.