LOW-TEMPERATURE GROWTH, FREEZING SURVIVAL, AND PRODUCTION OF ANTIFREEZE PROTEIN BY THE PLANT-GROWTH PROMOTING RHIZOBACTERIUM PSEUDOMONAS-PUTIDA GR12-2

The plant growth promoting rhizobacterium Pseudomonas putida GR12-2 wa s originally isolated from the rhizosphere of plants growing in the Ca nadian High Arctic. Here we report that this bacterium was able to gro w and promote root elongation of both spring and winter canola at 5 de grees C, a temperature at which only a relatively small number of bact eria are able to proliferate and function. In addition, the bacterium survived exposure to freezing temperatures,i.e., -20 and -50 degrees C . In an effort to determine the mechanistic basis for this behaviour, it was discovered that following growth at 5 degrees C, P. putida GR12 -2 synthesized and secreted to the growth medium a protein with antifr eeze activity. Analysis of the spent growth medium, following concentr ation by ultrafiltration, by SDS-polyacrylamide gel electrophoresis re vealed the presence of one major protein with a molecular mass of appr oximately 32-34 kDa and a number of minor proteins. However, at this p oint it is not known which of these proteins contains the antifreeze a ctivity.