Aerobic degradation of mixtures of chlorinated aliphatics by cloned toluene-o-xylene monooxygenase and toluene o-monooxygenase in resting cells.

Abstract

Recombinant strains of Escherichia coli constitutively expressing toluene-o-xylene monooxygenase (ToMO) of Pseudomonas stutzeri OX1 and toluene o-monooxygenase (TOM) of Burkholderia cepacia G4 were investigated for their ability to oxidize trichloroethylene (TCE), 1,1-dichloroethylene (1,1-DCE), cis-1,2-dichloroethylene (cis-DCE), trans-1,2-dichloroethylene (trans-DCE), vinyl chloride (VC), and chloroform (CF), individually as well as in various mixtures. ToMO oxidized all of these individual compounds well, whereas TOM did not degrade VC significantly (16-fold less) and degraded cis-DCE and trans-DCE less well (3.7- and 2.4-fold, respectively). For mixtures of these chlorinated aliphatics, ToMO was again more robust than TOM. For example, in binary mixtures including TCE, ToMO degraded all three DCE isomers and CF, but the presence of TCE inhibited VC degradation; TOM degraded both TCE/1,1-DCE and TCE/trans-DCE, but not cis-DCE for TCE/cis-DCE, and the addition of CF or VC to TCE completely inhibited degradation of both compounds and TCE. The addition of CF or trans-DCE stimulated VC degradation in the presence of TCE for ToMO, and the addition of any of the three DCE isomers stimulated VC degradation for TOM. Significant degradation of all ternary mixtures of TCE and less chlorinated ethenes, as well as a mixture of TCE, three DCEs, and VC, was achieved with ToMO (but not TOM). In mixtures of these chlorinated compounds, degradation was found to occur simultaneously rather than sequentially, and the mineralization of many of these compounds could be confirmed through detection of chloride ions.