A novel continuous toxicity test system using a luminously modified freshwater bacterium

Abstract

An automated continuous toxicity test system was developed using a recombinant bioluminescent freshwater bacterium. The groundwater-borne bacterium, Janthinobacterium lividum YH9-RC, was modified with luxAB and optimized for toxicity tests using different kinds of organic carbon compounds and heavy metals. luxAB-marked YH9-RC cells were much more sensitive (average 7.3–8.6 times) to chemicals used for toxicity detection than marine Vibrio fischeri cells used in the Microtox ® assay. Toxicity tests for wastewater samples using the YH9-RC-based toxicity assay showed that EC 50-5 min values in an untreated raw wastewater sample (23.9 ± 12.8%) were the lowest, while those in an effluent sample (76.7 ± 14.9%) were the highest. Lyophilization conditions were optimized in 384-multiwell plates containing bioluminescent bacteria that were pre-incubated for 15 min in 0.16 M of trehalose prior to freeze–drying, increasing the recovery of bioluminescence and viability by 50%. Luminously modified cells exposed to continuous phenol or wastewater stream showed a rapid decrease in bioluminescence, which fell below detectable range within 1 min. An advanced toxicity test system, featuring automated real-time toxicity monitoring and alerting functions, was designed and finely tuned. This novel continuous toxicity test system can be used for real-time biomonitoring of water toxicity, and can potentially be used as a biological early warning system.