CONDITIONED MEDIUM PROMOTES THE ATTACHMENT OF AGROBACTERIUM-TUMEFACIENS STRAIN NT1 TO CARROT CELLS

Wild-type Agrobacterium tumefaciens bind to carrot suspension culture cells. Avirulent strain NT 1 did not bind to carrot cells when they we re incubated together in Murashige and Skoog medium. Conditioned mediu m was prepared by incubating A, tumefaciens virulent strain C 58 with carrot cells and removing the bacteria and carrot cells using filter s terilization. This conditioned medium promoted the binding of NT 1 to carrot cells. Conditioned medium did not promote the nonspecific attac hment of Escherichia coli to carrot cells. These results suggest that when wild-type A. tumefaciens are incubated with plant host cells, som e substance(s) involved in bacterial attachment are released into the medium. Filter-sterilized medium from the incubation of the nonattachi ng chvB mutant A 1045 with carrot cells promoted the attachment of str ain NT 1 even though A 1045 bacteria did not bind to the carrot cells. However, filter-sterilized medium from the incubation of the nonattac hing att mutant Att-B 123 with carrot cells was unable to promote the binding of strain NT 1. This suggests that nonattaching mutants of A. tumefaciens can be divided into two groups on the basis of the propert ies of the substances released into the medium when the bacteria are i ncubated with carrot cells.