EXCHANGE OF CHROMOSOMAL MARKERS BY NATURAL TRANSFORMATION BETWEEN THE SOIL ISOLATE, PSEUDOMONAS-STUTZERI JM300, AND THE MARINE ISOLATE, PSEUDOMONAS-STUTZERI STRAIN ZOBELL

Both the soil isolate, Pseudomonas stutzeri JM300, and the marine isolate, Pseudomonas stutzeri strain ZoBell, have been shown previously to be naturally transformable. This study reports the detection of genetic exchange by natural transformation between these two isolates. Transformation frequency was determined by filter transformation procedures. Three independent antibiotic resistance loci were used as chromosomal markers to monitor this exchange event: resistance to rifampicin, streptomycin, and nalidixic acid. The maximum frequencies of transformation were on the order of 3.1 to 3.8 x 10(-6) transformants per recipient; frequencies over an order of magnitude greater than those for spontaneous antibiotic resistance, although they are lower than those observed for soil:soil or marine:marine strain crosses. This exchange was inhibited by DNase I. Transformation was observed between soil and marine strains, both by filter transformation using purified DNA solutions and when transforming DNA was added in the form of viable donor cells. The results from this study support the close genetic relationship between P. stutzeri JM300 and P. stutzeri strain ZoBell. These results also further validate the utility of P. stutzeri as a benchmark organism for modeling gene transfer by natural transformation in both soil and marine habitats.