In vitro degradation of pyrene was studied in MSM by three bacterial strains individually, designated as BP10, NJ2 and P2. Among these strains, NJ2 was the highest degrader (60%) of pyrene, followed by BP10 (44%) and the least was P2 (42%) in MSM with pyrene (50 mu g ml(-1)) in 8 days. During pyrene degradation, catechol 1,2 dioxygenase (C12O) activity was induced by 13 folds in BP10 and 17 folds in P2 as compared to catechol 2,3 dioxygenase (C23O). However, in NJ2, C23O activity was augmented 1.3 times more than C12O. This clearly indicated that C12O played a major role in pyrene degradation by BP10 and P2, while in NJ2, C23O contributed more to degradation process than C12O. Molecular weight of highly inducible C12O was determined as similar to 64 kDa by size exclusion chromatography and as similar to 32 kDa on denaturing SDS PAGE in BP10 which indicated dimeric nature of the enzyme. 2013 Elsevier Ltd. All rights reserved.