A SIMPLE MOST PROBABLE NUMBER TECHNIQUE FOR THE SENSITIVE RECOVERY OF A GENETICALLY-MODIFIED PSEUDOMONAS-AUREOFACIENS FROM SOIL

A strain of Pseudomonas aureofaciens (SBW25EeZY-6KX) that was chromosomally marked with a lacZY and a km(r)-xylE cassette could be recovered from non-sterile soil by a selective Pseudomonas enrichment broth amended with 100 ppm kanamycin and 50 ppm X-gal in an MPN (most probable number) assay. The assay was sensitive and reliable, allowing detection of as few as one recombinant cell in a 1% (w/v) soil suspension. The soil used contained a large (ca 5% of total culturable bacteria) background of indigenous bacteria that were either able to utilize lactose, were resistant to kanamycin, or both.