Stimulation and Molecular Characterization of Bacterial Perchlorate Degradation by Plant-Produced Electron Donors

Abstract

Root homogenate from poplar trees (Populus deltoides x nigra DN34, Imperial Carolina) stimulated perchlorate degradation in microcosms of soil and water samples collected at a perchlorate contaminated site, the Longhorn Army Ammunition Plant (LHAAP), located outside Karnack, Texas. Direct use of root products by perchlorate-degrading bacteria was shown for the first time as six pureculture bacteria isolated from LHAAP perchlorate-degrading microcosms degraded perchlorate when given root products as the sole exogenous source of carbon and electron donor. Nonenriched environmental consortia were able to utilize root products for perchlorate degradation, regardless of prior exposure to perchlorate. Microcosms that contained perchlorate-contaminated groundwater (MW-3) or uncontaminated surface water (Harrison Bayou) as inoculum degraded approximately 240 and 160 mg L(-1) perchlorate, respectively, using root products (approximately 440 mg L(-1) as COD) over 38 days. The predominant bacterial species in these aqueous microcosms, identified by DGGE, depended only upon the source inoculum as similar sequences were obtained whether root products or lactate was the electron donor. Sequences from DGGE bands that matched species within Dechloromonas, a genus consisting of many perchlorate degraders, were identified in all perchlorate-degrading microcosms. This study demonstrates the ability of root products to drive perchlorate respiration by bacteria and the potential for successful achievement of perchlorate rhizodegradation using in situ phytoremediation.