Horizontal transfer of genes of selective value in an environment 6 years after their introduction into a watershed has been observed. Expression of the gene pheA, which encodes phenol monooxygenase and is linked to the pheBA operon (A. Nurk, L. Kasak, and M. Kivisaar, Gene 102:13-18, 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 of 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, and U. Marklund, J. Bacteriol. 174:711-724, 1992), the pheA gene was also represented in the phenol-degrading strains. The area where the strains 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. stutzeri, and P. fluorescens biotypes B, C, and F) and harboring horizontally transferred pheBA operons were investigated. The phe genes were clustered 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 indicates that introduced genetic material could, if it encodes a beneficial capability, enrich the natural genetic variety for biodegradation.

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The processed oil shale (semi-coke) contains several organic and inorganic compounds (oil fractions, sulphides, phenolic compounds, polycyclic aromatic hydrocarbons) and is highly toxic. The solid waste deposit is a source of toxic phenolic leachate, which is discharged into nearby bodies of water without any treatment. Field experiments were carried out in order to test the effect of phytoremediation to enhance in-situ microbial biodegradation of pollutants in semi-coke. Four pilot test plots (50 m 2 ) were established at a semi-coke deposit in July 2001. The growth rate of plants was approximately twice higher in the case of soil amendment. The phytoremediation increased the number of biodegradative bacteria and diversity of microbial community in semi-coke. The presence and diversity of multi-component phenol hydroxylase (mPH) genes in the environment were assessed using the microbial DNA directly extracted from semi-coke. The changes in the genotypes of mPHs indicated shifts in the microbial community structure towards the more efficient degradation of pollutants due to plant treatment. Within a four-month period starting from the establishment of test plots in July, the concentration of phenolic compounds decreased three times in average and the concentration of oil products up to ten times, compared to the control plot.

Avoiding food-borne diseases by competitive exclusion agents is a proactive strategy. In the current paper, we report the use of Bacillus smithii TBMI12 spores as potential competitive exclusion agents. One group of mice was predosed for three successive days with 10(8) colony forming units of B. smithii TBMI12 spores followed by inoculation with 10(6) colony forming units of wild-type Salmonella enterica serotype Enteritidis cells. Microbial plate counts of the animals' livers and spleens showed that only 40% of the mice were infected with S. enterica serotype Enteritidis, while the control group was 100% infected. These results suggest that B. smithii TBMI12 spores may protect against infection by S. enterica serotype Enteritidis.