THE KINETICS OF TWO HETEROTROPHIC TETRACHLOROETHENE-RESPIRING POPULATIONS AND THEIR EFFECTS ON THE SUBSTRATE INTERACTIONS WITH DEHALOCOCCOIDES STRAINS

Abstract

This study focused on evaluating how interactions between the hydrogenotroph Dehalococcoides ethenogenes strain 195, which is able to completely dechlorinate tetrachloroethene (PCE) to ethene, and the two heterotrophs Desulfuromonas michiganensis strain BB1 and Desulfitobacterium sp. strain PCE1, which dechlorinate PCE to either cis-dichloroethene (cis-DCE) or trichloroethene (TCE), on the fate of PCE under common in situ bioremediation scenarios. Meaningful kinetic parameter estimates were obtained for the heterotrophic dehalorespirers under a wide range of conditions. Batch culture assays and numerical experiments were conducted with Desulfuromonas michiganensis to evaluate the effect of the initial conditions including the ratio of the initial substrate concentration (S0) to the initial biomass concentration (X0) and the ratio of S0 to the half-saturation constant (KS) on parameter correlation. Most importantly, S0/KS, but not S0/X0, strongly influenced parameter correlation. Correlation between the Monod kinetic parameters could be minimized by maximizing S0/KS.

In the present study, dechlorination of high PCE concentrations by Desulfuromonas michiganensis and Desulfitobacterium sp. strain PCE1 was monitored. The maximum level of PCE that could be dechlorinated by each strain was not constant, and varied with X0. This phenomenon could not be described using conventional Monod kinetics; therefore, a new model that incorporated an inactivation term into the biomass growth equation was developed to describe dechlorination at high PCE concentrations.

The interactions among Dehalococcoides ethenogenes and heterotrophic dehalorespirer in continuous-flow stirred tank reactors (CSTRs) were performed under two conditions that reflect either a natural attenuation or engineered bioremediation treatment scenario. Extant kinetic estimates accurately predicted the steady-state chlorinated ethene concentrations in the CSTRs. However, intrinsic kinetic parameter estimates better described the CSTR start-up phase. The modeling and experimental results suggested that the ability of Dehalococcoides ethenogenes to utilize PCE and TCE is limited by the presence of a PCE-to-TCE/cis-DCE dehalorespirer, which forces Dehalococcoides ethenogenes to function primarily as a cis-DCE-respiring population.

This study provides insight into how the activities of different dehalorespiring cultures are interrelated and will aid in the design of engineered bioremediation approaches that optimize the potential benefits associated with different dehalorespiring populations to achieve efficient and effective clean-up of PCE- and TCE-contaminated sites.