TOXICITY OF CHLOROBENZENES TO A LUX-MARKED TERRESTRIAL BACTERIUM, PSEUDOMONAS-FLUORESCENS

Insertion of lux genes, encoding for bioluminescence in naturally biol uminescent marine bacteria, into the genome of Pseudomonas fluorescens resulted in a bioluminescent strain of this terrestrial bacterium. Th e lux-marked bacterium was used to toxicity test the chlorobenzene ser ies. By correlating chlorobenzenes 50% effective concentration (EC50) values against physiochemical parameters, the physiochemical propertie s of chlorobenzenes that elicit toxic responses were investigated. The results showed that the more chlorinated the compounds, the more toxi c they were to lux-marked P. fluorescens. Furthermore, it was shown th at the more symmetrical the compound, the greater its toxicity to P, f luorescens. In general, the toxicity of a chlorobenzene was inversely proportional to its solubility (S) and directly proportional to its li pophilicity (K-ow). By correlating lux-marked P. fluorescens EC50 valu es, determined for chlorobenzenes, with toxicity values determined usi ng Pimephales promelas (fathead minnow). Cyclotella meneghiniana (diat om), and Vibrio fischeri (marine bacterium), it was apparent that lux- marked P. fluorescens correlated well with freshwater species such as the diatoms and fathead minnow but not with the bioluminescent marine bacterium V. fischeri. The implications of these findings are that a t errestrial bacterium such as P. fluorescens should be used for toxicit y testing of soils and freshwaters rather than the marine bacterium V. fischeri.