ACQUISITION OF A DELIBERATELY INTRODUCED PHENOL DEGRADATION OPERON, PHEBA, BY DIFFERENT INDIGENOUS PSEUDOMONAS SPECIES

Horizontal transfer of genes of selective value in an environment 6 ye ars after their introduction into a watershed has been observed. Expre ssion of the gene pheA, which encodes phenol monooxygenase and is link ed to the pheBA operon (A. Nurk, L. Kasak, and M. Kivisaar, Gene 102:1 3-18, 1991), allows pseudomonads to use phenol as a growth substrate. Pseudomonas putida strains carrying this operon on a plasmid were used for bioremediation after an accidental fire in the Estonia oil shale mine in Estonia in 1988. The water samples used for studying the fate of the genes introduced were collected in 1994. The same gene cluster was also detected in Pseudomonas strains isolated from water samples o f a nearby watershed which has been continuously polluted with phenols due to oil shale industry leachate. Together with the more frequently existing counterparts of the dmp genes (V. Shingler, J. Powlowski, an d U. Marklund, J. Bacteriol. 174:711-724, 1992), the pheA gene was als o represented in the phenol-degrading strains. The area where the stra ins containing the pheA gene were found was restricted to the regular route of phenolic leachate to the Baltic Sea. Nine Pseudomonas strains belonging to four different species (P. corrugata, P. fragi, P. stutz eri, and P. fluorescens biotypes B, C, and F) and harboring horizontal ly transferred pheBA operons were investigated. The phe genes were clu stered in the same manner in these nine phe operons and were connected to the same promoter as in the case of the original pheBA operon. One 10.6-kb plasmid carrying a pheBA gene cluster was sequenced, and the structure of the rearranged pheBA operon was described. This data indi cates that introduced genetic material could, if it encodes a benefici al capability, enrich the natural genetic variety for biodegradation.