Isolation and characterization of diverse halobenzoate-degrading denitrifying bacteria from soils and sediments

Denitrifying bacteria capable of degrading halobenzoates were isolated from various geographical and ecological sites. The strains were isolated after initial enrichment on one of the monofluoro-, monochloro-, or monobromo-be nzoate isomers with nitrate as an electron acceptor, yielding a total of 33 strains isolated from the different halobenzoate-utilizing enrichment cult ures. Each isolate could grow on the selected halobenzoate with nitrate as the terminal electron acceptor. The isolates obtained on 2-fluorobenzoate c ould use 2-fluorobenzoate under both aerobic: and denitrifying conditions, but did not degrade other halobenzoates. In contrast, the 4-fluorobenzoate isolates degraded 4-fluorobenzoate under denitrifying conditions only, but utilized 2-fluorobenzoate under both aerobic and denitrifying conditions. T he strains isolated on either 3-chlorobenzoate or 3-bromobenzoate could use 3-chlorobenzoate, 3-bromobenzoate, and 2- and 4-fluorobenzoates under deni trifying conditions, The isolates were identified and classified on the bas is of 16S rRNA gene sequence analysis and their cellular fatty acid profile s. They were placed in nine genera belonging to either the alpha-, beta-, o r gamma-branch of the Proteobacteria. namely, Acidovarax, Azoarcus, Bradyrh izobium, Ochrobactrum, Paracoccus, Pseudomonas, Mesorhizabium, Ensifer, and Thauera. These results indicate that the ability to utilize different halo benzoates under denitrifying conditions is ubiquitously distributed in the Proteobacteria and that these bacteria are widely distributed in soils and sediments.