Biodegradation of CVOCs and 1,4-Dioxane Mixtures by Engineered Microbial Communities

Dr. Shaily Mahendra | University of California, Los Angeles

ER-2713

Objective

This proof of concept research project will focus on designing anaerobic/aerobic engineered microbial communities to adapt to various redox regimes as well as simultaneously biodegrade chlorinated volatile organic compounds (CVOCs) and 1,4-dioxane in contaminated aquifers. Mixtures of CVOCs and 1,4-dioxane are commonly found as groundwater co-contaminants at many DoD sites. Biological degradation of CVOCs as well as 1,4-dioxane has been previously reported, but occurs independently in reductive and oxidative processes, respectively. Moreover, recent work indicates that certain CVOCs actually inhibit aerobic biodegradation of 1,4-dioxane.

ER-2713 Photo

Building upon the quantitative and mechanistic insights gained in SERDP project ER-2300 about how CVOC co-contaminants affect 1,4-dioxane biodegradation, microbial co-cultures will be proactively designed to overcome inhibition and biodegrade multiple contaminants. This effort would lead to cost savings and improved remedial strategies for CVOCs and 1,4-dioxane mixtures. The hypothesis is that the inhibitory effects of CVOCs on 1,4-dioxane biodegradation rates will be mitigated by designing a microbial community that mineralizes CVOCs as well as 1,4-dioxane, and this will be tested via the following objectives:

  1. Design and test microbial communities composed of anaerobic and aerobic contaminant degrading bacteria to simultaneously or sequentially degrade mixtures of trichloroethene (TCE), 1,1-dichloroethene (1,1-DCE), cis-1,2-dichloroethene (cDCE), and 1,4-dioxane;
  2. Elucidate the influence of oxygen dose and timing on the individual biodegradation rates and overall contaminant mass removal by the engineered microbial community; and
  3. Determine the population, diversity, and biodegradation activity of the engineered microbial communities in groundwater microcosms using molecular biomarkers and high throughput sequencing technologies.

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Technical Approach

In laboratory studies, the TCE dechlorinating microbial culture KB-1, containing Dehalococcoides (Dhc) as the CVOC-dechlorinating culture, and CB1190 and OB3b representing aerobic CVOC- and 1,4-dioxane-metabolizing and co-metabolizing strains, will be selected as the major components for constructing a defined anaerobic/aerobic microbial community. Growth will be determined by increases in abundance of 16S rRNA genes specific to KB-1, CB1190, and OB3b using qPCR. The viability of engineered microbial communities under various independent and transitioning redox conditions will be quantified by streak plating, ATP analysis, or PMA-qPCR, to navigate a potential go/no-go decision. The biodegradation kinetics of CVOCs and 1,4-dioxane mixtures in the engineered microbial communities will be evaluated using pure cultures as well as contaminated environmental samples. Field conditions will be simulated represented by low oxygen content to identify the minimum requirements for complete biodegradation of CVOC and 1,4-dioxane by members of the engineered microbial community. Molecular biological tools (gene abundance, gene expression, and next generation sequencing) will be applied for microbial population quantification, functional gene expression, and community structure analysis.

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Benefits

This research will support SERDP’s mission to reduce the DoD’s liabilities by developing sustainable, cost-effective technologies for expedited site cleanup and closure by in situ remediation of 1,4-dioxane and CVOC contamination in groundwater. The design of the anaerobic/aerobic microbial community will contribute to a better understanding of the microbial community’s adaptations to various redox conditions and avoid production of undesirable intermediates. Furthermore, this will serve as a guide for the optimization of bioaugmentation and biostimulation efforts thereby developing the optimum short and long-term remedial strategies for mixed contamination. Results from this project will help the DoD with the decision process of when and how to transition from active remediation to enhanced attenuation of CVOCs and 1,4-dioxane. (Anticipated Project Completion - 2018)

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Points of Contact

Principal Investigator

Dr. Shaily Mahendra

University of California, Los Angeles

Phone: 310-794-9850

Fax: 310-206-2222

Program Manager

Environmental Restoration

SERDP and ESTCP

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