Optimization of bacterial whole cell bioreporters for toxicity assay of environmental samples

In a study to optimize bacterial whole cell biosensors (bioreporters) for the detection of environmental contaminants, we constructed a toxicity sensing strain Acinetobacter baylyi ADP1_recA_lux. The ADP1_recA_lux is a chromosomally based bioreporter which makes the sensing system stable and negates the need for antibiotics to maintain the trait. The AOP1_recA_lux is activated to express bioluminescence when it is exposed to DNA damaging toxicants. Since the ADP1_recA_lux constantly expresses a baseline level of bioluminescence, false negative results are avoided. The host strain, A. baylyi ADP1, is an ideal model strain typical of water and soil bacteria occurring in the natural environment, and it is more robust than E. coli in terms of viability, maintenance, and storage. The expression of reporter genes - luxCDABE cloned from Photorhabdus luminescens - is robust in a broad range of temperature (10-40 degrees C). The ADP1_recA_lux was used to detect a variety of toxic or potentially toxic compounds including mitomycin C (MMC), methyl methanesulfonate, ethidium bromide, H2O2, toluene, single-wall nanocarbon tubes (SWNCT), nano Au colloids (20 nm), pyrene, beno[a]pyrene, and UV light. These exposures revealed that the ADP1_recA_lux was able to detect both genotoxicity and cytoxicity, qualitatively and quantitatively. The optimal induction time of the ADP1_recA_lux bioreporter was 3 h, and the detection limits for MMC and benezo[a]pyrene were 1.5 nM and 0.4 nM, respectively. The ADP1_recA_lux was also used to detect toxicity of groundwater contaminated by a mixture of phenolic compounds, and the bioreporter toxicity detection was in a good agreement with chemical analysis. The optimized whole cell bioreporter ADP1_recA_lux could be valuable in providing a simple, rapid, stable, quantitative, robust, and costly efficient approach for the detection of toxicity in environmental samples.