Engineered global regulator H-NS improves the acid tolerance of E. coli

• Published in: Microbial cell factories Vol. 17; no. 1; p. 118
• Main Authors: Gao, Xianxing, Yang, Xiaofeng, Li, Jiahui, Zhang, Yan, Chen, Ping, Lin, Zhanglin
• Format: Journal Article
• Language: English
• Published: England BioMed Central Ltd 27.07.2018; BioMed Central; BMC
• Subjects: Acetic acid; Acid resistance; Acid tolerance; Acidification; Acidity; Bacteria; Bacterial proteins; Byproducts; Chemical properties; Comparative analysis; Denaturation; Deoxyribonucleic acid; DNA; DNA damage; E coli; Engineering; Enzymes; Error-prone PCR; Escherichia coli; Fermentation; Gene expression; Genomes; Genotype & phenotype; Global transcription machinery engineering (gTME); Glutamine; Growth rate; H-NS; Metabolism; Metabolites; Methods; Microbiological research; Microorganisms; Mutagenesis; Mutants; pH effects; Phenotypes; Proteins; Regulators; Repressors; Stress; Stress (Physiology); Stress response; Succinic acid; Transcription; Error-prone PCR; H-NS; Acid tolerance; E. coli; Global transcription machinery engineering (gTME)
• ISSN: 1475-2859; 1475-2859
• DOI: 10.1186/s12934-018-0966-z

Acid stress is often encountered during industrial fermentation as a result of the accumulation of acidic metabolites. Acid stress increases the intracellular acidity and can cause DNA damage and denaturation of essential enzymes, thus leading to a decrease of growth and fermentation yields. Although acid stress can be relieved by addition of a base to the medium, fermentations with acid-tolerant strains are generally considered much more efficient and cost-effective. In this study, the global regulator H-NS was found to have significant influence on the acid tolerance of E. coli. The final OD of strains overexpressing H-NS increased by 24% compared to control, when cultured for 24 h at pH 4.5 using HCl as an acid agent. To further improve the acid tolerance, a library of H-NS was constructed by error-prone PCR and subjected to selection. Five mutants that conferred a significant growth advantage compared to the control strain were obtained. The final OD of strains harboring the five H-NS mutants was enhanced by 26-53%, and their survival rate was increased by 10- to 100-fold at pH 2.5. Further investigation showed that the improved acid tolerance of H-NS mutants coincides with the activation of multiple acid resistance mechanisms, in particular the glutamate- and glutamine-dependent acid resistance system (AR2). The improved acid tolerance of H-NS mutants was also demonstrated in media acidified by acetic acid and succinic acid, which are common acidic fermentation by-products or products. The results obtained in this work demonstrate that the engineering of H-NS can enhance the acid tolerance of E. coli. More in general, this study shows the potential of the engineering of global regulators acting as repressors, such as H-NS, as a promising method to obtain phenotypes of interest. This approach could expand the spectrum of application of global transcription machinery engineering.