A Calcium- and Magnesium-Tolerant Enterobacter sp. MTT Respiratory Inhibition Assay for Rapid Screening of Mercury and Silver in Industrial River Water
DOI:
https://doi.org/10.54987/jebat.v8i2.1191Keywords:
Whole-cell bioassay, Enterobacter, Mercury, Silver, Effect-based monitoringAbstract
Rapid biological screening can complement instrumental analysis by identifying water samples that warrant priority investigation. This study developed a whole-cell respiratory inhibition assay based on the reduction of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) by a locally isolated bacterium. Enterobacter sp. strain DRY13, retained respiratory activity in the presence of Ca2+ and Mg2+ yet responded strongly to toxic metals. supported tentative placement within Enterobacter. Among 13 metals tested, Ag+ and Hg2+ produced greater than 50% inhibition at 10 mg L−1. One-phase exponential models yielded IC50 values of 0.139 mg L−1 for Ag+ (95% CI, 0.115–0.173 mg L−1) and 0.144 mg L−1 for Hg2+ (95% CI, 0.106–0.221 mg L−1), with R2 values of 0.9842 and 0.999, respectively. The reported limits of detection were 0.0033 mg L−1 for Ag+ and 0.0216 mg L−1 for Hg2+; corresponding limits of quantification were 0.0294 and 0.0386 mg L−1. Most pesticides and solvent-related xenobiotics caused little inhibition at the tested concentrations, whereas sodium dodecyl sulfate was a notable interferent. River and industrial-estate samples inhibited MTT reduction, while tap water did not. Because ICP-AES measures total recoverable metal whereas whole-cell inhibition reflects the combined bioavailable toxic fraction, the assay is best interpreted as a rapid effect-based screen rather than a metal-specific quantitative method. The platform provides a simple basis for prioritizing contaminated samples for confirmatory instrumental analysis.
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