The development and application of a bioassay using lux-marked microorganisms to assess terrestrial ecotoxicity
Bioluminescent bacteria have been shown to offer a rapid, reproducible and inexpensive basis for ecotoxicity assessment. The ability to insert lux genes, responsible for bioluminescence, into terrestrial bacteria enabled the development for a bioluminescence-based bioassay that used environmentally relevant microgranisms. The metabolic response induced by the pollutant on the organisms was measured in terms of bioluminescence change. The ecotoxicity test was optimised and made highly reproducible. An ecotoxicity assay using lux-marked constructs of Pseudomonas fluroescens (a ubiquitious rhizosphere bacterium) and Rhizobium leguminosarum biovar trifolii (an important associative nitrogen fixer) was found to be more sensitive to a range of metals in aqueous solution than conventional microbial assays. The lux-based bioassay was also found to be valid over a wide pH range and in buffered and non-buffered samples. Soil water was extracted from a range of soils and spiked with metals. The results that extracts from a range of soils differed in their capacity to change the bioavailability of metals. The lux-based bioassay was found to be very sensitive to metal pollutants in soil water. The lux-based bioassay was used to study the effect of pollutants in three contrasting environments. The first study was the examination of Cu toxicity from a whisky distillery. There was a strong correlation between the bioluminescence response of lux-marked Ps. fluorescens and Cu concentration. The second study involved an assessment of soil extracts from the Lee Valley sewage sludge experiments. The third study was carried out in the USA, testing sediment samples from the Grand Calumet and Detroit Rivers.