Characterisation of a thermostable catechol-2,3-dioxygenase from phenanthrene-degrading Pseudomonas sp strain ZJF08

Four strains with high phenanthrene-degrading ability were isolated from petroleum badly polluted soil. The strain Pseudomonas sp. ZJF08 demonstrated the highest rate of degradation (138.1 mg center dot L-1 center dot day(-1)) among them and degraded 97.1% of the phenanthrene in one week. The activities of two key enzymes of ZJF08, polycyclic aromatic hydrocarbon dioxygenase and catechol-2,3-oxygenase (C230), were also assayed during the degradation of phenanthrene. Both of them reached their maximums on the 2(nd) day of degradation. The C230 gene (C7) of Pseudomonas sp. ZJF08 was cloned and expressed in Escherichia coli, and its gene product was purified by a Ni-NTA-agarose column. The optimum temperature for the purified C230 was 40 degrees C at pH 7.5 and the C230 activity could be still detected when the temperature reached 70 degrees C. The results showed that the C230 from Pseudomonas sp. strain ZJF08 exhibited better thermostability than its homologs reported.