Use of a lux-marked rhizobacterium as a biosensor to assess changes in rhizosphere C flow due to pollutant stress

The flow of carbon from plant roots into soil supports a range of microbial processes and is therefore critical to ecosystem function and health. Poll ution-induced stress, which influences rhizosphere C flow is of considerabl e potential importance, and therefore needs to be evaluated. This paper rep orts on a method, based on reporter gene technology, for quantifying pollut ant effects on rhizosphere C flow. The method uses the lux-marked rhizobact erium Pseudomonas fluorescens, where bioluminescence output of this biosens or is directly correlated with the metabolic activity and reports on C flow in root exudate. Plantago lanceolata was treated with paraquat (representi ng a model pollutant stress) in a simple microcosm system. The lux-biosenso r response correlated closely with C concentrations in the exudate and demo nstrated that the pollutant stress increased the C flow from the plantago r oots, 24 h after application of the herbicide, The lux-reporter system ther efore potentially offers a technique for use in assessing the impact of pol lutant stress on rhizosphere C flow through the soil microbial biomass. (C) 2000 Elsevier Science Ltd. All rights reserved.