Emerging Contaminants Summit

Spring 2020

StudentCompetitionpolaskoAlexandra Polasko
Ph.D. Student
University of California Los Angeles

Alexandra Polasko is a 3rd year Ph.D. student in the Department of Civil and Environmental Engineering. She obtained her B.S. from UC Berkeley in environmental science with an emphasis in microbiology. Before entering Dr. Shaily Mahendra's lab group, Alexandra worked in Dr. Lisa Alvarez-Cohen's lab researching the effects of sulfate and sulfide on chlorinated solvent biodegradation. She recently was a finalist in the American Society of Microbiology International Agar Art contest. Her plate will be on display in the Exhibition Hall at the New Orleans Ernest N. Morial Convention Center, as well as, online and on Facebook. 


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

Authors: Alexandra Polasko, Jiahui Wang, Shu Zhang, Shaily Mahendra 

Chlorinated Volatile Organic Compounds (CVOCs) and 1,4-dioxane (dioxane) are often commingled groundwater contaminants due to improper storage, discharges, and accidental spills. Bioremediation is an effective approach for removing these pollutants. Anaerobic biological reduction is a common remediation tactic for CVOCs. Under some conditions, intermediate daughter products such as cis-1,2-dichloroethene (cDCE) and vinyl chloride (a known carcinogen) are accumulated. Aerobic biodegradation of CVOCs is challenging due to the additional amendments required by cometabolizers. Dioxane is often biodegraded aerobically, and no anaerobic biodegradation pathways have been identified yet. The opposing redox conditions favored by CVOC- and dioxane-degrading bacteria pose a difficult problem for concurrent bioremediation of both contaminants. We engineered a microbial community composed of previously identified anaerobic (KB1) and aerobic (Pseudonocardia dioxanivorans CB1190 (CB9110))  bacteria in modified medium to simultaneously or sequentially degrade CVOCs and dioxane. Results showed that the aerobic dioxane degrader, CB1190, was able to survive anaerobic incubation and reactivate the monooxygenase enzyme. After 24 hours of anaerobic incubation, CB1190 degraded dioxane at a rate of 8.661.1 mg L-1 day-1 and upregulated the dxmB and aldH genes 2-fold. The engineered anaerobic-aerobic culture was able to degrade TCE at a rate of 2208.1µg L-1hr-1 and dioxane at a rate of 31338µg L-1 hr-1. Also, the engineered mixed microbial culture was able to biodegrade dioxane at an order of magnitude higher rate than the pure aerobic culture. As a plume disperses throughout the saturated zone, the redox conditions frequently change from anaerobic (source zone) to aerobic (downgradient). The engineered microbial community can survive these changes and biodegrade both CVOCs and dioxane. This approach could reduce the cost, energy, and substrates required for in situ bioremediation for CVOCs and dioxane. 



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