R-2-(4-Hydroxyphenoxy)propionic acid (R-HPPA) is a pivotal intermediate for the synthesis of aryloxyphenoxypropionate (APP) herbicide. To rapidly screen microbial isolates with the capacity of hydroxylating R-2-phenoxypropionic acid to R-HPPA from various environmental samples, a convenient and safe 96-well microplate assay method with sodium nitrite (NaNO₂) as chromogenic reagent was proposed and optimized. The optimum assay conditions were as follows: the detection wavelength was 420 nm, the concentration of NaNO₂ solution was 6.0 g/L, color reaction temperature was 60 °C, the pH of the NaNO₂ solution was 2.4, and the reaction time was 40 min. With the aid of this method, screening for microorganisms with C-4-specific hydroxylation activity of R-PPA was conducted. As a result, 23 strains among 3744 single colonies isolated from various samples exhibited the hydroxylation activity. Among these strains, the highest bioconversion rate was achieved by Penicillium oxalicum A5 and Aspergillus versicolor A12, respectively. After 72-h cultivation in shake flask, their conversion rates of R-HPPA from 10 g/L R-PPA reached 21.18% and 40.24%, respectively. The established method was effective in rapid screening of microbes capable of biosynthesizing R-HPPA through hydroxylation of R-PPA, and the obtained two fungi species could be potentially used for R-HPPA production.

R -2-（4-羟基苯氧基）丙酸（R -HPPA）是合成芳氧基苯氧基丙酸酯（APP）除草剂的关键中间体。为了从各种环境样品中快速筛选具有将R -2-苯氧基丙酸羟化为R -HPPA的能力的微生物分离物，提出并优化了一种方便安全的以亚硝酸钠（NaNO ₂）为生色试剂的96孔微孔板测定方法。最佳测定条件如下：检测波长为420 nm，NaNO ₂溶液浓度为6.0 g / L，显色反应温度为60°C，NaNO ₂的pH溶液为2.4，反应时间为40分钟。借助于该方法，进行了具有R -PPA的C-4特异性羟基化活性的微生物的筛选。结果，从各种样品中分离出的3744个单菌落中有23个菌株表现出羟化活性。在这些菌株中，分别通过草酸青霉A5和杂色曲霉A12实现了最高的生物转化率。在摇瓶中培养72小时后，R -HPPA从10 g / L R -PPA的转化率分别达到21.18％和40.24％。所建立的方法有效地快速筛选了能够通过羟基化合成R- HPPA的微生物。R -PPA和获得的两种真菌可能被潜在地用于R -HPPA生产。