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. 2014 Oct 1:71:215-222.
doi: 10.1016/j.ecoleng.2014.07.046.

Enhanced Polychlorinated Biphenyl Removal in a Switchgrass Rhizosphere by Bioaugmentation with Burkholderia xenovorans LB400

Yi Liang  1 , Richard Meggo  1 , Dingfei Hu  1 , Jerald L Schnoor  1 , Timothy E Mattes  1
Affiliations

Enhanced Polychlorinated Biphenyl Removal in a Switchgrass Rhizosphere by Bioaugmentation with Burkholderia xenovorans LB400

Yi Liang et al. Ecol Eng. .

Abstract

Phytoremediation makes use of plants and associated microorganisms to clean up soils and sediments contaminated with inorganic and organic pollutants. In this study, switchgrass (Panicum virgatum) was used to test for its efficiency in improving the removal of three specific polychlorinated biphenyl (PCB) congeners (PCB 52, 77 and 153) in soil microcosms. The congeners were chosen for their ubiquity, toxicity, and recalcitrance. After 24 weeks of incubation, loss of 39.9 ± 0.41% of total PCB molar mass was observed in switchgrass treated soil, significantly higher than in unplanted soil (29.5 ± 3.4%) (p<0.05). The improved PCB removal in switchgrass treated soils could be explained by phytoextraction processes and enhanced microbial activity in the rhizosphere. Bioaugmentation with Burkholderia xenovorans LB400 was performed to further enhance aerobic PCB degradation. The presence of LB400 was associated with improved degradation of PCB 52, but not PCB 77 or PCB 153. Increased abundances of bphA (a functional gene that codes for a subunit of PCB-degrading biphenyl dioxygenase in bacteria) and its transcript were observed after bioaugmentation. The highest total PCB removal was observed in switchgrass treated soil with LB400 bioaugmentation (47.3 ± 1.22 %), and the presence of switchgrass facilitated LB400 survival in the soil. Overall, our results suggest the combined use of phytoremediation and bioaugmentation could be an efficient and sustainable strategy to eliminate recalcitrant PCB congeners and remediate PCB-contaminated soil.

Keywords: Burkholderia xenovorans LB400; PCBs; biphenyl dioxygenase gene; phytoextraction; switchgrass.

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Figures

Figure 1
Figure 1
The percentage of initial molar concentrations for total PCB (orange), PCB 52 (green), PCB 77 (blue), and PCB 153(purple) after 12 weeks and 24 weeks incubation in unplanted soil (UP), switchgrass treated soil (SG), unplanted with bioaugmentaion soil (UP B), switchgrass treated with bioaugmentation soil (SG B), and switchgrass treated with bioaugmentation with dead LB400 soil (SG BD). Error bars indicate the standard deviation of three soil subsamples from the same reactor.
Figure 2
Figure 2
qPCR analysis of (A) bacterial 16S rRNA genes and (B) bphA abundance with time in blank (BLK), PCB spiked and unplanted soil (UP), PCB spiked and switchgrass treated soil (SG). Error bars indicate the range of two soil subsamples from the same reactor.
Figure 3
Figure 3
qPCR analysis of bacterial 16S rRNA gene (A) and bphA (B) abundance with time in switchgrass treated soil (SG), switchgrass treated soil with bioaugmentation (SG B), switchgrass treated soil with autoclaved LB400 bioaugmention (SG BD); and bacterial 16S rRNA gene (C)and bphA (D) inunplanted soil (UP), unplanted soil with LB400 bioaugmentation (UP B), switchgrass treated soil with bioaugmentation (SG B). Error bars indicate the range of two soil subsamples from the same reactor.
Figure 4
Figure 4
qPCR analysis of bphA transcripts with time in unplanted soil with bioaugmentation (UP B), and switchgrass treated soil with bioaugmention (SG B). Error bars indicate the range of two soil subsamples from the same reactor.
Figure 5
Figure 5
qPCR analysis of LB400 16S–23S ITS abundance with time in unplanted soil with bioaugmentation (UP B), and switchgrass treatedsoil with bioaugmention (SG B). Error bars indicate the range of two soil subsamples from the same reactor.
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