Rhizosphere microbial activity during phytoremediation of diesel-contaminated soil

Jaisoo Kim, Seung Hee Kang, Kyung Ah Min, Kyung Suk Cho, In Sook Lee

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30 Scopus citations

Abstract

To know microbial activity and diesel-removal efficiency influencing through plant roots, we examined the effect of the rhizosphere on phytoremediation of diesel-contaminated soils by alfalfa (Medicago sativa L.). Pots were treated with and without diesel and allowed to stabilize for 7 weeks, at which time four experimental/control groups were prepared: (1) planted diesel-contaminated soil, (2) unplanted diesel-contaminated soil, (3) planted uncontaminated soil, and (4) unplanted uncontaminated soil. Samples of rhizosphere and bulk soils were separately taken from all planted pots. After 7 weeks of alfalfa growth from seeds, the removal efficiencies in rhizosphere and bulk soil samples were 82.5% and 36.5 59.4%, respectively. The total microbial activity was highest in diesel-contaminated rhizosphere soils. Significantly more culturable soil bacteria and hydrocarbon-degraders were found in diesel-contaminated rhizosphere soil versus unplanted and uncontaminated bulk soil, with a greater increase seen in hydrocarbon-degraders (172-fold) versus general soil bacteria (14-fold). DGGE (Denaturing Gel Gradient Electrophoresis) analysis revealed that the bacterial community structure was most highly influenced by the combined presence of diesel contamination and plant roots (39.13% similarity compared to the control), but that diesel contamination alone had a higher influence (42.31% similarity compared to the control) than the rhizosphere (50.00% similarity compared to the control). Sequence analysis and BLAST searches revealed that all samples were dominated by members of α -, γ -, δ - and ε -proteobacteria, and Chloroflexi. The rhizosphere samples additionally contained novel dominant members of α -proteobacteria and Cytophaga-Flexibacter-Bacteroides, while the diesel samples contained additional dominant α -proteobacteria and the rhizosphere plus diesel samples contained other ε -proteobacteria. Collectively, these findings indicate that the presence of plant roots (i.e., a rhizosphere) had a greater effect on bacterial activity in diesel contamination than did the absence of diesel contamination, whereas diesel contamination had a greater effect on bacterial community structure. These novel findings provide new insight into the mechanisms of phytoremediation.

Original languageEnglish
Pages (from-to)2503-2516
Number of pages14
JournalJournal of Environmental Science and Health - Part A Toxic/Hazardous Substances and Environmental Engineering
Volume41
Issue number11
DOIs
StatePublished - 1 Nov 2006

Keywords

  • Alfalfa
  • Bacterial community structure
  • Bulk
  • DGGE (Denaturing Gel Gradient Electrophoresis)
  • Diesel
  • Medicago sativa L.
  • Microbial activity
  • Phytoremediation
  • Rhizosphere
  • Soil

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