Evidence for plasmid-mediated chemotaxis of Pseudomonas putida towards naphthalene and salicylate

A naphthalene (Nap) and salicylate (Sal) degrading microorganism, Pseudomon as putida RKJ1, is chemotactic towards these compounds. This strain carries a 83 kb plasmid. A 25 kb EcoRI fragment of the plasmid contains the genes responsible for Nap degradation through Sal. RKJ5, the plasmid-cured deriva tive of RKJ1, is neither capable of degradation nor is chemotactic towards Nap or Sal. The recombinant plasmid pRKJ3, which contained a 25 kb EcoRI fr agment, was transferred back into the plasmid-free wild-type strain RKJ5, a nd the transconjugant showed both degradation and chemotaxis. The recombina nt plasmid pRKJ3 was also transferred into motile, plasmid-free P. putida K T2442. The resulting transconjugant (RKJ15) showed chemotaxis towards both Nap and Sal. Two mutant strains carrying deletions in pRKJ3 (in KT2442) wit h phenotypes Nap(-) Sal(+) and Nap(-) Sal(-), were also tested for chemotax is. It was found that the Nap(-) Sal(+) mutant strain showed chemotaxis tow ards Sal only, whereas the Nap(-) Sal(-) mutant strain is non-chemotactic t owards both the compounds. These results suggest that the metabolism of Nap and Sal may be required for the chemotactic activity.