A study Was conducted to compare the diversity of 2-,3-,and 4-chlorobenzoate degraders in two pristine soils and one contaminated sewage sludge.These samples contained strikingly different populations of mono-chlorobenzoate degraders.Although fewer cultures were isolated in the uncontaminated soils than contaminated one,the ability of microbial populations to mineralize chlorobenzoate was widespread.The 3-and 4-chlorobenzoate degraders were more diverse than me 2-chlorobenzoate degraders.One of the strains isolated from the sewage sludge was obtained.Based on its phenotype.chemotaxonomic properties and 16S rRNA gene,the organism S-7was classified as Rhodococcus erythropolis.The strain can grow at temperature from 4 to 37℃.C.It can utilize several(halo)aromatic compounds.Moreover,strain S-7 can grow and use 3-chlorobenzoate as sole carbon source in a temperatures range of 10-30℃ with stoichiometric release of chloride ions.The psychrotolerant ability was significant for bioremediation in low temperature regions.Catechol and chlorocatechol 1,2-dioxygenase activities were present in cell free extracts of the strain,but no(chloro)catechol 2,3-dioxygenase activities was detected.Spectral conversion assays with extracts from R.erythropolis S-7 showed accumulation of a compound with a similar UV spectrum as chloro-cis,cis-muconate from 3-chlorobenzoate.On the basis of these results,we proposed that S-7 degraded 3-chlorobenzoate through the modified ortho-cleave pathway.