A qualitative and quantitative high-throughput assay for screening of gluconate high-yield strains by Aspergillus niger

•We developed a two-step selection strategy to screen large libraries of mutants.•Bromocresol green was added in media resulted in a real-time monitoring system.•Three effective mutants were screened out by high-throughput screening strategy.

A novel two-step high-throughput strategy was developed for screening of gluconate high-yield strains by Aspergillus niger. The first step was fast qualitative assay according to the indicator color change, the second step was quantitative assay according to the absorbance of chelate formed with Cu2 + at 810 nm. The accuracy of high-throughput assay was comparable to that of high-performance liquid chromatography (HPLC). The correlation coefficient between CuSO4 assay and HPLC assays was exceeding 0.99 by statistical analysis. As a result, 3 high-yield mutants were screened out from 1000 viable single colonies, the mutants II-2-A1, IV-7-C6, and V-11-C5 were further validated in 5 L of bioreactor. The average production rates were 15.5%, 32.8%, and 12.1% higher than that of the parental strain, respectively.