ACS Synth. Biol. https://doi.org/10.1021/acssynbio.0c00089 (2020)

The microbial production of certain compounds benefits from the use of specialized conditions, such as temperature and pH extremes, to which commonly used organisms such as Escherichia coli are not naturally resistant. To make E. coli acid tolerant, de Siqueira et al. drew on metagenome sequences to construct new synthetic ‘acid resistance clusters’ consisting of three genes encoding extremophile homologs of the DNA-binding protein HU, an RNA-binding protein, and the protease ClpP. Using a combinatorial approach, the authors generated a panel of synthetic operons using these genes with varied ribosome-binding sequences (RBSs) and screened for their ability to confer acid resistance in E. coli. While each gene alone improved cellular viability at pH 1.9, the three together exhibited a synergistic advantage and enhanced E. coli survival by 100-fold relative to the empty vector. Although future work is needed to construct improved strains with increasingly robust acid tolerance, this engineering effort demonstrates the potential of using synthetic operons to confer the benefit of multiple resistance genes on an industrially useful microbe.