Toluene degradation pathway from Pseudomonas putida F1: substrate specificity and gene induction by 1-substituted benzenes

The metabolism of n-alkylbenzenes (C₃–C₇), biphenyl, styrene and cumene by the tod pathway from Pseudomonas putida F1 was examined in terms of catabolism by the pathway enzymes and the inducibility of the tod operon. F1 cells grown on toluene exhibited oxygen consumption in the presence of the compounds examined. Toluene dioxygenase (TDO) catalyzed the formation of monol, cis-dihydrodiol and triol metabolites from the n-alkylbenzenes tested and the triol formed from n-propylbenzene was metabolized to the derivative, 2-hydroxy-6-oxohexa-2,4-dienoate (HOHD), by subsequent enzymes in the tod pathway. Biotransformation of the tested compounds with toluene-grown F1 cells resulted in the accumulation of ring cleavage HOHD derivatives; the metabolites were inefficiently metabolized by cell extracts of toluene-grown F1 cells, indicating that 6-methyl-HOHD hydrolase encoded by todF might be a determinant for the further degradation of the selected 1-substituted benzenes. The results obtained from enzyme activity assays and reverse transcription polymerase chain reaction (RT-PCR) showed that not only growth-supporting substrates, but also n-propylbenzene, styrene and cumene act as inducers of the tod operon. Journal of Industrial Microbiology & Biotechnology (2000) 25, 163–170.