OVERCOMING THE METABOLIC LOAD ASSOCIATED WITH THE PRESENCE OF PLASMIDDNA IN THE PLANT-GROWTH PROMOTING RHIZOBACTERIUM PSEUDOMONAS-PUTIDA GR12-2

When the broad host range plasmid vector pGSS15 was used to geneticall y transform the plant growth promoting rhizobacterium Pseudomonas puti da GR12-2, the transformants were physiologically debilitated. It was postulated that the expression of the beta-lactamase gene of pGSS15 ca used a metabolic load resulting in the impaired functioning of the bac terium. To test this hypothesis, derivatives of pGSS15 that either lac k the beta-lactamase gene (pYH12-2) or in which a beta-glucosidase gen e was substituted for the beta-lactamase gene (pYH124) were constructe d and examined to see whether their presence also impaired the functio ning of P. putida GR12-2. On the basis of growth rates, siderophore pr oduction, and the ability to stimulate canola root elongation in steri le growth pouches, neither of the newly constructed plasmids debilitat ed P. putida GR12-2. In addition, P. putida GR12-2 transformed with pY H124 facilitated the proliferation of the bacterium in minimal medium containing cellobiose at low temperature. This latter trait may enable P. puticia GR12-2 to persist in the soil in competition with other mi croorganisms.