title: Natural attenuation is enhanced in previously contaminated and coniferous forest soils.
abstract: OBJECTIVE
  Prevalence of organic pollutants or their natural analogs in soil is often assumed to lead to adaptation in the bacterial community, which results in enhanced bioremediation if the soil is later contaminated. In this study, the effects of soil type and contamination history on diesel oil degradation and bacterial adaptation were studied.
  
  
  METHODS
  Mesocosms of mineral and organic forest soil (humus) were artificially treated with diesel oil, and oil hydrocarbon concentrations (GC-FID), bacterial community composition (denaturing gradient gel electrophoresis, DGGE), and oil hydrocarbon degraders (DGGE + sequencing of 16S rRNA genes) were monitored for 20 weeks at 16°C.
  
  
  RESULTS
  Degradation was advanced in previously contaminated soils as compared with pristine soils and in coniferous organic forest soil as compared with mineral soil. Contamination affected bacterial community composition especially in the pristine mineral soil, where diesel addition increased the number of strong bands in the DGGE gel. Sequencing of cloned 16S rRNA gene fragments and DGGE bands showed that potential oil-degrading bacteria were found in mineral and organic soils and in both pristine and previously contaminated mesocosms. Fast oil degradation was not associated with the presence of any particular bacterial strain in soil.
  
  
  CONCLUSIONS
  We demonstrate at the mesocosm scale that previously contaminated and coniferous organic soils are superior environments for fast oil degradation as compared with pristine and mineral soil environments. These results may be utilized in preventing soil pollution and planning soil remediation.
authors.affiliation: Department of Environmental Sciences, Section of Ecology, University of Helsinki, Lahti, Finland.
authors.forename: Sari
authors.initials: S
authors.lastname: Kauppi
authors.forename: Martin
authors.initials: M
authors.lastname: Romantschuk
authors.forename: Rauni
authors.initials: R
authors.lastname: Strömmer
authors.forename: Aki
authors.initials: A
authors.lastname: Sinkkonen
mesh_terms: D001673:Biodegradation, Environmental; D058645:Denaturing Gradient Gel Electrophoresis; D005742:Gasoline / Q000382:microbiology* / Q000633:toxicity; D006838:Hydrocarbons / Q000378:metabolism* / Q000633:toxicity; D008903:Minerals / Q000378:metabolism / Q000633:toxicity; D012336:RNA, Ribosomal, 16S / Q000378:metabolism; D012988:Soil Microbiology; D012989:Soil Pollutants / Q000378:metabolism* / Q000633:toxicity; D014197:Trees
chemical_list: D005742:Gasoline; D006838:Hydrocarbons; D008903:Minerals; D012336:RNA, Ribosomal, 16S; D012989:Soil Pollutants