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Toxic compounds in effluent wastewater can have a negative affect on the quality and perfommance of activated sludge systems. Monitoring the efffluent wastewaters by chemical analysis and periodic bioassays is often too slow in response to avoid problems. Detection of bioluminescence in certain bacteria with the luciferase enzyme coded by the lux gene can provide quick and early toxicity information. The bioluminescence is correlated to metabolic activity. Bacteria containing the luciferase enzyme will bioluminate under ideal conditions, and should decrease as conditions decline. This rapid response may help to overcome many of the limitations of traditional wastewater monitoring methods. A bioluminescent reporter in the bacterium Pseudomonas fluorescens (developed at the University of Tennessee, Knoxville) is being evaluated to determine if bioluminescence is a suitable indicator of toxicants in wastewater effluent. Bacteria containing the luciferase enzyme and a tetracycline resistance gene are grown in nutrient broth amended with 10 parts per million of tetracycline in batch cultures at 25 °C. After 48 hours the bacteria cultures are tested for bioluminescence using a modified fluorometer. The bioluminescent cultures are standardized to 900 fluorescence standard units and are used for dose-response bioassays. Toxins, such as sodium hypochlorite or heavy metals, are added to the cultures in known concentrations. Changes in bioluminescence are measured as a response to the toxins. Early results indicate that a 0.02 percent sodium hypochlorite solution elicits an immediate decrease in bioluminescence. Nickel (Ni2+) and lead (Pb2+) also elicit a rapid decrease in bioluminescence. However, other toxicants such as zinc (Zn2+) and sodium thiosulfate enhance bioluminescence at low concentrations (0.1 to 1.0 parts per million), but decrease in original bioluminescence by 50 percent at 100 parts per million. Organic chemicals will also eventually be tested as part of this evaluation.
U.S. Department of the Interior, U.S. Geological Survey
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