Impact of bioaccessible pyrene on the abundance of antibiotic resistance genes during Sphingobium sp.- and sophorolipid-enhanced bioremediation in soil

Soils are exposed to various types of chemical contaminants due to anthropogenic activities; however, research on persistent organic pollutants and the existence of antibiotic resistance genes (ARGs) is limited. To our knowledge, the present work for the first time focused on the bioremediation of soil co-contaminated with pyrene and tetracycline/sulfonamide-resistance genes. After 90 days of incubation, the pyrene concentration and the abundance of the four ARGs (tetW, tetM, sulI, and sun!) significantly decreased in different treatment conditions (p < 0.05). The greatest pyrene removal (47.8%) and greatest decrease in ARC abundance (from 10(-7) to 10(-8) ARC copies per 16S rRNA copy) were observed in microcosms with a combination of bacterial and sophorolipid treatment. Throughout the incubation, pyrene bioaccessibility constantly declined in the microcosm inoculated with bacteria. However, an increased pyrene bioaccessibility and ARC abundance at day 40 were observed in soil treated with sophorolipid alone. Tenax extraction methods and linear correlation analysis indicated a strong positive relationship between the rapidly desorbing fraction (F-r) of pyrene and ARC abundance. Therefore, we conclude that bioaccessible pyrene rather than total pyrene plays a major role in the maintenance and fluctuation of ARC abundance in the soil. (C) 2015 Elsevier B.V. All rights reserved.