Luminescence-Based Bioassays. The luminescencebased bioassays consisted of two microorganisms with the
genes encoding bacterial luminescence inserted into them.
The organisms used were E. coli HB101 pUCD607 and P.
fluorescens 10586rs pUCD607. The E. coli and P. fluorescens
biosensors were resuscitated from freeze-dried vials following
the protocols of Duffy (16) and Paton et al. (11), respectively.
All bioassays consisted of adding 50 íL of the appropriate
cell suspension to 450 íL of the test solution in a cuvette at
15 s intervals. The luminescence of the cells was then
measured in a Bio-Orbit 1253 luminometer after exposure
times of 145 and 15 min for E. coli and P. fluorescens,
respectively. These exposure times were chosen because, in
preliminary studies (data not shown), they gave optimum
response from the biosensors to pollutants in soil pore water.
All bioassays were carried out in triplicate, and the luminescence was expressed as a percentage of the luminescence
measured in soil pore water from control treatments, which
received uncontaminated sludge