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Applied and Environmental Microbiology, July 2002, p. 3502-3508, Vol. 68, No. 7
0099-2240/02/$04.00+0     DOI: 10.1128/AEM.68.7.3502-3508.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Solid-Phase Contact Assay That Uses a lux-Marked Nitrosomonas europaea Reporter Strain To Estimate Toxicity of Bioavailable Linear Alkylbenzene Sulfonate in Soil

Kristian K. Brandt,* Anders Pedersen, and Jan Sørensen

Section of Genetics and Microbiology, Department of Ecology, Royal Veterinary and Agricultural University, Frederiksberg, Denmark

Received 27 November 2001/ Accepted 4 April 2002

Information about in situ toxicity of the bioavailable pools of adsorptive soil pollutants is a prerequisite for proper ecological risk assessment in contaminated soils. Such toxicity data may be obtained by assays allowing for direct exposure of introduced test microorganisms to the toxicants, as they appear in solid solution equilibria in the natural soil. We describe a novel sensitive solid-phase contact assay for in situ toxicity testing of soil pollutants based on a recombinant bioluminescent reporter strain of Nitrosomonas europaea. A slurry of the reporter strain and soil sample was shaken for 1 h, after which bioluminescence was measured either directly (soil slurry protocol) or in the supernatant obtained after centrifugation (soil extract protocol). The assay was validated for both protocols by using linear alkylbenzene sulfonate (LAS) as a toxic and adsorptive model compound in the soil samples. Interestingly, LAS showed the same toxicity to the reporter strain with either soil incubation (both protocols) or pure culture, suggesting that adsorbed LAS pools contributed to the observed toxicity. The solid-phase contact assay that used the reporter strain of lux-marked N. europaea was slightly more sensitive for the detection of LAS toxicity in soil than activity-based assays targeting indigenous nitrifiers and much more sensitive than assays targeting indigenous heterotrophic microbes. We conclude that the new solid-phase contact assay, which is based on direct interaction of the test microorganisms with bioavailable pools of the toxicants in soil, provides a most sensitive and relevant method for evaluating the in situ toxicity and assessing the risks of soil contaminants.

* Corresponding author. Present address: Center for Microbial Ecology, Michigan State University, 540 Plant and Soil Science Building, East Lansing, MI 48824. Phone: (517) 353-7858. Fax: (517) 353-2917. E-mail: kkb{at}kvl.dk.

Applied and Environmental Microbiology, July 2002, p. 3502-3508, Vol. 68, No. 7
0099-2240/02/$04.00+0     DOI: 10.1128/AEM.68.7.3502-3508.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.





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