Heterogeneity of Stop Codon Readthrough in Single Bacterial Cells and Implications for Population Fitness

Gene expression noise (heterogeneity) leads to phenotypic diversity among isogenic individual cells. Our current understanding of gene expression noise is mostly limited to transcription, as separating translational noise from transcriptional noise has been challenging. It also remains unclear how translational heterogeneity originates. Using a transcription-normalized reporter system, we discovered that stop codon readthrough is heterogeneous among single cells, and individual cells with higher UGA readthrough grow faster from stationary phase. Our work also revealed that individual cells with lower protein synthesis levels exhibited higher UGA readthrough, which was confirmed with ribosome-targeting antibiotics (e.g., chloramphenicol). Further experiments and mathematical modeling suggest that varied competition between ternary complexes and release factors perturbs the UGA readthrough level. Our results indicate that fluctuations in the concentrations of translational components lead to UGA readthrough heterogeneity among single cells, which enhances phenotypic diversity of the genetically identical population and facilitates its adaptation to changing environments. [Display omitted] •Stop codon readthrough is heterogeneous among single cells•Increased UGA readthrough promotes bacterial growth•Reducing protein synthesis levels enhances UGA readthrough•Fluctuations of translational components lead to UGA readthrough heterogeneity Protein synthesis accuracy is important for cell physiology and has been mostly studied at the population level. Fan et al. develop a dual-reporter system to quantitate protein synthesis errors in single bacterial cells and show that slowing protein synthesis increases some translational errors, namely readthrough of stop codons.