Whole-cell recombinant bacterial sensors


Many current analytical techniques used for monitoring pollutants require expensive equipment and extensive pretreatment of the environmental samples. Whole-cell biosensors offer significant advantages over conventional analytical methods providing data on the bioavailability of a pollutant as well as on its effects on living cells. Moreover, complex pretreatment of the environmental sample (typical prior chemical analysis) is usually not needed for biosensor measurements. In addition, information on bioavailability of pollutant(s) is very valuable for risk assessment purposes and for the selection of suitable remediation schemes.

The sensing principle

Whole-cell bacterial biosensors typically combine a promoter-operator, which acts as the sensing element, with reporter gene(s) coding for easily detectable proteins. Sensor element usually consists of a specific promoter fused to the reporter gene, and a gene encoding for a transcription factor that in response to certain chemical or a group of chemicals activates the promoter. Under normal conditions, this activation would lead to the synthesis of proteins, the presence or activity of which would help the cell combat the sensed hazard or adapt to it. In the recombinant strain the selected promoter drives the synthesis of the reporter protein(s).

Our sensors, cooperation and results

In our laboratory and in cooperation of Dr. Marko Virta’s group (University of Helsinki, Finland), we have developed whole cell bacterial sensors for mercury (including organic mercury), chromate, zinc and phenolic compounds. In addition we have applied biosensors for cadmium and lead.

Regulatory units used in the construction of metal-specific sensor bacteria originate from bacteria that possess natural precisely regulated resistance systems towards heavy metals (for example, znt from E. coli, mer operon from Serratia marcescens, chr operon from Ralstonia eutropha), whereas sensing element for sensor that recognises phenolic compounds originates from Pseudomonas sp. CF600 that are capable of metabolising phenols (dmp metabolic pathway). As a reporter we have employed either firefly luciferase (lucFF) or bacterial luciferase (luxCDABE operon).

As living cells are complex, and the light output of bioluminescent sensors depends not only on the chemical complexity of the sample, i.e. the type and quantity of inducers present, but also on the physiological state of the cells at the time of measurement, we have used constitutively luminescent bacteria as a control strains in parallel with sensor bacteria to obtain a relevant information about the interference on the luminescence which is not caused by the target analyte. These control bacteria are similar to sensor bacteria (same host and reporter), but lack the sensor element. All the sensors have been applied in environmental testing determining bioavailable amount of heavy metals from soils (heavily polluted soils from surroundings of metal smelters), sediments (from Baltic Sea) and wastewater samples. Phenol sensor has been applied on leachates and groundwater samples from oil shale industry region in North-East Estonia.

At the moment our interest is focused on improving the sensitivity and specificity of heavy metal sensor bacteria, especially we are interested in constructing a Pb-specific and Zn-specific biosensors.

For other bioassays, see Biotests

Our relevant publications

Ivask, A., Hakkila, K., Virta, M. (2001) Detection of organomercurials with sensor bacteria. Analytical Chemistry 73(21): 5168-5171

Ivask, A., Virta, M., Kahru, A. (2002) Construction and use of specific luminescent recombinant bacterial sensors for the assessment of bioavailable fraction of cadmium, zinc, mercury and chromium in the soil – Soil Biol. & Biochem., 34: 1439-1447.

Ivask, A., Bernaus, A. (2004) "Assessment of sorption and bioavailability of mercury compounds in soils and sediments" SENSPOL: European Network on Sensors for Monitoring Water Pollution Newsletter no. 11, p. 18-2

Hakkila, K., Green, T., Leskinen, P., Ivask, A., Marks, R., Virta, M. (2004) Detection of bioavailable heavy metals in EILATOX-Oregon samples using whole-cell luminescent bacterial sensors in suspension or immobilized onto fibre-opric tips.- J. Applied Toxicology, 24: 333-342

Anna Bernaus, Xavier Gaona, Angela Ivask, Anne Kahru, Manuel Valiente (2005) Analysis of sorption and bioavailability of different species of mercury on model soil components using XAS techniques and sensor bacteria –Analytical and Bioanalytical Chemistry,  382 (7),  p. 1541 - 1548

Pasi Peltola, Angela Ivask, Mats Åström and Marko Virta (2005) Lead and Cu in contaminated urban soils: Extraction with chemical reagents and bioluminescent bacteria and yeast. - Science of The Total Environment, In Press, Corrected Proof, Available online 23 March 2005.

Kahru, A., Ivask, A., Kasemets, A., Põllumaa, L., Kurvet, I., Francois, M., Dubourguier, HC. (2005) Biotests and biosensors in ecotoxicological risk assessment of field soils polluted with zinc, lead and cadmium – Environmental Toxicology & Chemistry, Vol. 24, No. 11, in press.

Anu Leedjärv, Angela Ivask, Anne Kahru, Marko Virta Construction and use of recombinant luminescent bacterial sensor for the analysis of bioavailable phenols from natural samples – in preparation for Environmental Toxicology

Keemilise ja Bioloogilise Füüsika Instituut


Group of Ecotoxicology* Ökotoksikoloogia grupp


Reporter protein




Reporter gene

Sensor protein

Principle of whole cell recombinant biosensors:

When analyte binds to the sensor protein a transcription of reporter gene is activated, this results in higher amount reporter protein (luciferase) and therefore luminescence increases. At higher analyte concentrations luminescence decreases due to the toxicity of analyte.

Text Box: Luminescent response