Semester of Graduation

Spring 2023

Degree

Master of Science (MS)

Department

Civil and Environmental Engineering

Document Type

Thesis

Abstract

At a Superfund site near Baton Rouge, LA, the subsurface injection of molasses has been used to stimulate anerobic reductive dechlorination of halogenated organic compounds (e.g., 1,2-dichloroethane and vinyl chloride) present in the groundwater. Following some molasses injections, temporary accumulation of toluene and p-cresol was observed in the groundwater. Accumulation of these aromatic hydrocarbons, which were not detected in the molasses, has been attributed to anaerobic biotransformation of the amino acids phenylalanine and tyrosine. Experiments reported here were conducted in support of an effort to determine if toluene biodegrading bacteria were present in the area where anaerobic toluene accumulation was reported. Enrichment cultures inoculated with site groundwater were established in anoxic freshwater medium supplemented with either nitrate or sulfate. Toluene consumption was observed in time series experiments with both terminal electron acceptors. PCR with primers targeting two genes associated with anaerobic toluene transformation were used with community DNA extracts as template. The enzymes produced by the targeted genes included benzylsuccinate synthase and 6-oxocyclohex-1-ene-1-carbonyl-coenzyme A hydrolase (6- OCH-CoA). Sequencing of PCR amplicons confirmed gene target identity. PCR amplicons were most closely related to gene sequences from Aromatoleum petrolei strain ToN1 and Desulforhabdus amnigenus strain PRTOL1. Collectively, data demonstrate that microorganisms capable of anaerobically degrading toluene are present in groundwater in the area where toluene biogenesis was observed, providing a potential mechanistic explanation for decreases in toluene concentrations at the field site following temporary increases in site groundwater.

Date

1-17-2023

Committee Chair

Moe, William

DOI

10.31390/gradschool_theses.5696

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