Bacterial assay for quantitative measurement of nanomolar concentrations of a metabolite.

A mutant of Pseudomonas fluorescens was used to develop a radioligand, competitive binding assay to quantitatively measure gamma-aminobutyric acid. The highly reliable and reproducible assay was sensitive (nM detection), rapid, and easy to perform. Nonspecific activity and scatter were insignificant. Radiolabel was irreversibly fixed by the cells in an energy-dependent reaction. The finding that a bacterium was effective in quantitatively detecting nanomolar amounts of a metabolite suggests that other bacteria or their mutants might be used in competitive binding assays to detect and quantify amino acids or other substances occurring in trace amounts.