Effect of Acetonitrile on RDX Biodegradation in an Unsaturated Surface Soil

摘要

In previous work, we documented the biodegradation of hexahydro-1,3, 5- trinitro-1,3,5-triazine (RDX) in an unsaturated cold-region surface soil and showed that acetonitrile (ACN) could inhibit RDX removal rates when used as a dispersant for the contaminant. Here, we document that the added ACN had an effect on microbial community development in the RDX-contaminated soil. In the absence of ACN, the soils showed a striking increase in microbial biomass and in biomarkers indicative of microfauna. A four-fold increase in the phospholipid fatty acid (PLFA) biomarkers 18:2w6 and 20:4w6 (approximately 4-16 mol %) coincided with a greater than two-fold increase in total microbial biomass (approximately 15-35 nmol g(-1) PLFA). In the presence of ACN (1% aqueous concentration), these increases were not observed. The ACN-free soils also showed a significant decrease in PLFA biomarkers for Gram-negative bacteria (i.e., approximately 15 mol% decrease in w7 monounsaturated PLFA). This decrease was not observed in soils amended with 1% ACN. We concluded that the organic solvent interfered with microbial community development, specifically the trophic interaction between free-living protozoa and Gram- negative bacteria. Since the addition of 1% ACN increased the half-life for RDX from 29 to 48 days, the trophic interaction may be a necessary component in the development of an RDX-biodegrading microbial community.