Occurrence and some properties of aerobic psychrophilic soil bacteria

Summary The occurrence of aerobic psychrophilic bacteria in different types of soil was studied in regard to all the bacteria present. They constitute a considerable percentage of all the bacteria present in the soils investigated and represent a constant component of the soil microflora, irrespective of the season of the year. They are almost exclusively rod-like, half Gram-negative and half Gram-positive, non-sporulating organisms. It was found, however, that their reaction to Gram-straining varies and depends on the incubation temperature. The temperature of 35°C inhibited the growth of about 40 per cent of the selected psychrophilic strains and caused the development of involutionary forms in 37 per cent of the strains grown. The psychrophilic bacteria isolated from the soils mostly showed ability to decompose urea, and were concerned with ammonification of peptones and reduction of nitrates.Due attention was also given to the problem of adequate incubation temperature in the investigations on soil microorganisms.