Revealing novel synergistic defense and acid tolerant performance of Escherichia coli in response to organic acid stimulation.

Escherichia coli is an important producer of mono- and di-acids, such as D-lactic acid, itaconic acid, and succinic acid. However, E. coli has limited acid tolerance and requires neutralizers in large-scale fermentation, which leads to increased production costs. Mutagenesis breeding has been shown to be inefficient in improving the acid tolerance of strains. Therefore, it is crucial to analyze the acid resistance mechanism of E. coli. To this end, important regulatory genes and metabolic pathways in the highly evolved acid-resistant E. coli were identified based on transcriptome sequencing. By analyzing the overlap of the genes with significantly different expression levels in the four groups, a synergistic membrane-centric defense mechanism for E. coli against organic acid stress was identified. The mechanism includes four modules: signal perception, energy countermeasures, input conditioning, and envelope reinforcement. In addition, genes related to the ABC transporter pathway, polyketide metabolism, pyrimidine metabolism, and dual-arginine translocation system pathways were found for the first time to be potentially resistant to organic acid stress after overexpression. A new antacid ingredient, RffG, increases the survival rate of E. coli by 4509.6 times. This study provides new clues for improving the performance of acid-tolerant cells and reducing the production cost of industrial organic acid fermentation. KEY POINTS: • Systematic analysis of the mechanism of membrane protein partitioning in E. coli to resist organic acids • TAT system transports correctly folded hydrogenase accessory proteins to resist D-lactic acid stress • Enhanced PG synthesis and weakened hydrolysis to reduce acid penetration into cells • Overexpression of RffG in the polyketide synthesis pathway enhances acid tolerance.