A model that uses the induction phase of lux gene-dependent bioluminescence in Pseudomonas fluorescens HK44 to quantify cell density in translucent porous media

A cooled charge-coupled device (CCD) camera was used to follow the kinetics of induction of lux gene-dependent bioluminescence in Pseudomonas fluoresc ens HK44 held either in aqueous suspensions minus sand. saturated or unsatu rated translucent sand (0.348 and 0.07 cm(3) H2O/cm(3) of sand, respectivel y), and at cell densities ranging between I x 10(6) and 8.5 x 10(8) cells/m l. Before O-2 availability became a limiting factor, the rate of light emis sion (L) increased with the square of time (t) and linearly with increasing cell density (c). A nonlinear model was developed that contains a "rate of increase in light emission" constant, B', which is determined directly fro m the slope of a plot of rootL/c against t. The model predicted the behavio r of lux induction in HK44 under a variety of conditions. Similar B' values were determined [49.0-57.6 x 10(-10) light units/(cell min(2))] for cell s uspensions held in aqueous medium minus sand, in saturated or unsaturated 4 0/50 grade sand (0.36 mm grain diameter) and in two other textural classes of translucent sand. Although both the growth phase, and the presence of gl ucose during lux induction affected the first detectable time (FDT) of biol uminescence by HK44 in sand, the kinetics of induction of light emission we re similar among treatments (stationary phase cells plus glucose, B' = 61.6 +/- 3.2, log phase cells plus glucose, B' = 63.2 +/- 7.2). The potential e xists to use a combination of a CCD camera system, an inducible lux gene co ntaining bioluminescent bacterium, and a light transmission chamber to noni ntrusively visualize and quantify in real time the interactions between bac terial growth and unsaturated flow of water and solutes in porous media. (C ) 2001 Elsevier Science B.V. All rights reserved.