A rapid throughput assay for screening (R)-2-(4-hydroxyphenoxy)propionic acid producing microbes

( R )-2-(4-hydroxyphenoxy)propionic acid (( R )-HPOPA) is an important intermediate for the synthesis of optically pure aryloxyphenoxypropionic acid herbicides. Regioselective hydroxylation of ( R )-2-phenoxypropionic acid (( R )-POPA) by microbes is one of the most useful methods for the industrial production of ( R )-HPOPA. In this study, we designed and optimized a rapid throughput assay for screening ( R )-HPOPA producing bacterial/fungal strains which can regioselectively hydroxylate ( R )-POPA. ( R )-HPOPA could react with 4-aminoantipyrine (4-AAP) in the presence of potassium hexacyanoferrate (K 3 [Fe(CN) 6 ]) to form indoxyl antipyrine, an orange-red chromophore, that can easily spectrophotometrically be determined at 550 nm. During the verification of the assay we observed an average recovery rate of between 97.3% and 104.5%. Apart from the rapid throughput, no obvious differences in detection ( R )-HPOPA in the culture broth samples were found between our rapid throughput multiplate assay and a high-performance liquid chromatography method. Our optimized assay method is simple, rapid and accurate with high repeatability. It has the potential for high throughput screening (about 3000–5000 samples/day) of the ( R )-HPOPA producing strains.