Assessing the bioavailability of organic pollutants in surfactant solutions using a novel bioluminescent biosensor

Bioavailability is often considered to be the rate limiting process in the bioremediation of sites contaminated with hydrophobic organic compounds (HOCs). In order to meet the need for a direct measurement technique for microbial bioavailability, the whole-cell bioluminescent biosensor PpF1G4 was developed. To create PpF1G4, bioluminescent reporter genes (lux) were placed under the control of the promoter region of the solvent efflux pump genes (sep) in Pseudomonas putida F1. In screening experiments, it was determined that biosensor PpF1G4 produced a bioluminescent response to a wide range of aromatic compounds.PpF1G4 was used to evaluate how three nonionic surfactants (Triton X-100, Brij 30 and Brij 35) influence the bioavailability of three different HOCs (toluene, naphthalene, and phenanthrene). Nonionic surfactants were used because they are in general less toxic to bacteria. The increased bioluminescent response of PpF1G4 in micellar solutions of Triton X-100 and Brij 35 indicated higher intra-cellular concentrations of the test compounds, toluene, naphthalene and phenanthrene, compared to control systems with no surfactants present. In contrast, Brij 30 caused a decrease in the bioluminescent response to the test compounds. The effect of the micellar solutions on the toluene biodegradation rate was consistent with the bioluminescent response. Thus, the bioluminescent response of PpF1G4 was an accurate indicator of bioavailability. The results suggest that nonionic surfactants enhance biodegradation in two ways: (1) by augmenting membrane permeability through binding of surfactant monomers; and (2) by increasing the mass flux of substrates present in the micellar pseudophase to the cells.PpF1G4 was also employed to evaluate the bioavailability of HOCs partitioned from multicomponent NAPLs (gasoline, crude oil, and creosote) into surfactant solutions. All three surfactants tested increased the bioavailability of HOCs partitioned from creosote and crude oil. None of the surfactants significantly enhanced the response to gasoline-equilibrated solutions. The suppression of bioluminescence in Brij 30 solutions containing single test compounds did not occur in Brij 30 solutions containing multiple HOCs. This research sheds some light on how certain nonionic surfactants may increase the bioavailability of HOCs and thus enhance bioremediation