Pgas, a Low-pH-Induced Promoter, as a Tool for Dynamic Control of Gene Expression for Metabolic Engineering of Aspergillus niger.

The dynamic control of gene expression is important for adjusting fluxes in order to obtain desired products and achieve appropriate cell growth, particularly when the synthesis of a desired product drains metabolites required for cell growth. For dynamic gene expression, a promoter responsive to a particular environmental stressor is vital. Here, we report a low pH-inducible promoter, P gas , which promotes minimal gene expression at pH values of greater than 5.0, but functioned efficiently at low pH values, such as pH 2.0. First, we performed a transcriptional analysis of Aspergillus niger , an excellent platform for the production of organic acids, and found that the promoter P gas may act efficiently at low pH. Then, synthetic green fluorescent protein ( sGFP ) was successfully expressed by P gas at pH 2.0, verifying the results of the transcriptional analysis. Next, P gas was used to express the cis -aconitate decarboxylase ( cad ) gene of A. terreus in A. niger , allowing the production of itaconic acid at a titer of 4.92 g/L. Finally, we found that P gas strength was independent of acid type and acid ion concentration, showing dependence on pH only. Importance: This promoter can be used for the dynamic control of gene expression in A. niger metabolic engineering to produce organic acids. This promoter may also be a candidate tool for genetic engineering.