Microcosm Assessment of Polaromonas sp. JS666 as a Bioaugmentation Agent for Degradation of cis-1,2-dichloroethene in Aerobic,Subsurface Environments

Chlorinated ethenes such as tetrachloroethene and trichloroethene have been widely used as dry-cleaning and degreasing solvents. Under anaerobic conditions, microorganisms reduce these parent compounds to less-chlorinated daughter products such as cis-1,2-dichloroethene (cDCE), and often further to ethene. This process can be stalled at cDCE, due to insufficient supply of reductants and/or inadequate microbial-community composition. Recently, a novel bacterium, Polaromonas sp. JS666, was isolated that is able to aerobically oxidize cDCE as sole carbon and energy source. As such, it is a promising candidate for use as a subsurface, bioaugmentation agent at sites where anaerobic bioremediation is inappropriate or has stalled and cDCE has migrated to, and accumulated within, aerobic zones, or where it is practical to impose aerobic conditions. Subsurface sediments or groundwater from six such cDCE-contaminated sites were used to construct microcosms. In every sediment or groundwater inoculated with JS666, the organism was able to degrade cDCE, provided that the pH remained circum-neutral. Even when JS666 was challenged with an alternate carbon source, or in the presence of competitive/predatory microorganisms, there was a measure of success. Collectively, these microcosm studies suggest that JS666 is a viable candidate for the bioaugmentation of aerobic, cDCE-contaminated sites. A minimum inoculation level in excess of 10⁵ cells per mL is recommended for field applications. At this level of inoculation, 100 L of inoculum culture grown to an OD600 of 1.0 should be able to treat a 10-m × 30-m × 80-m (24,000-m³) plot.