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A bacterial consortium was enriched from a saline soil contaminated by crude oil using phenanthrene as the sole source of carbon and energy at 10% salinity.The bacterial consortium can degrade 100 mg/L of phenanthrene within 4 days.Two halotolerant catechol 2,3-dioxygenases (C23O1 and C23O2), cloned from the halophilic bacterial consortium, were firstly identified and biochemically characterized.Amino acid sequences of two catechol 2,3-dioxygenases shared the greatest homology with the known isoenzymes from Marinobacter algicola sp.DG893 HP15.C23O1, C23O2 and its similar proteins can be classified into a novel family.C23O1 and C23O2 represented a novel halotolerant member of the catechol 2,3-dioxygenase family.When the two C23Os were purified from the overexpressing transformant and characterized, they showed high C23O activity and were not inhibited by NaCl.C23Os were firstly found to maintain actively and remarkably stable in range of 0-30% salinity.The optimal temperature for C23O1 and C23O2 was 40 ℃ and 60 ℃, respectively.Both two C23O enzymes could degrade effectively 3-methylcatechol, 4-methylcatechol, and 4-chlorocatechol, except 1, 2-dihydroxnaphthalene.This is the first report describing the cloning, expression and functional characterization of C23O encoding genes from halophiles capable of degrading phenanthrene.The high activity of C23O enzymes in salty environment makes the genes attractive for developing industrial and bioremediation applications in saline environment.