Development and characterization of a lux-modified 2,4-dichlorophenol-degrading Burkholderia sp RASC

lux-marked biosensors for assessing the toxicity and bioremediation potential of polluted environments may complement traditional chemical techniques. luxCDABE genes were introduced into the chromosome of the 2,4-dichlorophenol (2,4-DCP)-mineralizing bacterium, Burkholderia sp. RASC c2, by biparental mating using the Tn4431 system. Experiments revealed that light output was constitutive and related to cell biomass concentration during exponential growth. The transposon insertion was stable and did not interrupt 2,4-DCP-degradative genes, and expression of luxCDABE did not constitute a metabolic burden to the cell. A bioluminescence response was detectable at sublethal 2,4-DCP concentrations: at <10.26 mu g ml(-1) bioluminescence was stimulated (e.g. 218% of control), but at concentrations >60 mu g ml(-1) it declined to <1%. Investigating the effect of [C-14]-2,4-DCP concentration on the evolution of (CO2)-C-14 revealed that, for initial concentrations of 2.5-25 mu g ml(-1), approximate to 55% of the added C-14 was mineralized after 24 h compared with <1% at 50 and 100 mu g ml(-1). Inhibition of 2,4-DCP mineralization between 25 and 50 mu g ml(-1) corresponded well to the EC50 value (33.83 mu g ml(-1)) obtained from bioluminescence inhibition studies. lux-marked RASC c2 may therefore be used as a functionally (i.e. 2,4-DCP degrader) and environmentally relevant biosensor of toxicity and biodegradation inhibition.