Aromatic hydrocarbon degradation patterns and catechol 2,3-dioxygenase genes in microbial cultures from deep anoxic hypersaline lakes in the eastern Mediterranean sea

Several mixed cultures able to grow on different aromatic hydrocarbons were obtained from different depths (between 3500 and 3660 m under the sea surf ace) of water/brine interfaces (1 to 5 m over the estimated brine surface) of three deep hypersaline anoxic basins (Urania, Discovery and Atalante) in the eastern Mediterranean sea. Eight strains which completely removed tolu ene from the medium in six to IO days were isolated from one of the mixed c ultures obtained from the Urania basin. The strains grew on toluene and yea st extract in the presence of NaCl concentrations of up to 50 and 100 g 1(- 1), respectively, indicating that they are halotolerant rather than halophi lic. Even though DNA fingerprinting methods showed that the strains were st rictly related, two groups could be found on the basis of the plasmid profi le. Metabolic profiling and partial sequencing (350 bp) of the 16S rDNA sho wed that the strains were related to Pseudomonas mendocina. A 320 bp fragme nt of the catechol 2,3-dioxygenase gene from all the strains was aimplified by PCR. The sequence of the fragment showed 100% identity with xylE from p WW53 of Pseudomonas putida MT53 isolated from soil. Southern hybridisation experiments showed that catechol 2,3-dioxygenase is plasmid encoded.