Reviewer #1 (Public Review):
The research titled "Spatial and temporal distribution of ribosomes in single cells reveals aging differences between old and new daughters of Escherichia coli" by Lin Chao, Chun Kuen Chen, Chao Shi, and Camilla U. Rang addresses the asymmetric distribution of ribosomes in single E. coli cells during aging by time-lapse microscopy, as well as its correlation to protein misfolding. The presented research is an important contribution to the field of protein biosynthesis pathways and their link to aging, especially in regard to the thorough analysis of variation in cell elongation rate in old and new daughter cells derived from old and new mother cells. However, the imaging results, analysis, and methodologies require substantial elaboration, as in its current form several key characteristics remain unanswered. Furthermore, the results should be compared and discussed in regard to several other reports, which analyzed ribosome asymmetric distribution and inheritance in E.coli, see detailed comments below.
Major comments:<br />
*It is not clear from the results or the material and methods sections how the authors define and detect old vs. new mother cells up to 128 cells division, which is the limit the manuscript describes in line 574: "To avoid effects of crowding within the micro-colonies, movies were ended when micro-colonies exceeded 128 cells". The results described only refer to 3 cell divisions (Fig.1 for example). As this is the key issue the manuscript addresses this requires elaboration.
* The authors should present several representative images of the results described, including: "New daughters at birth from old mothers have more ribosomes" - this should include clear quantification, of normalized fluorescence intensity vs. normalized cell length, as well as for "Ribosomal asymmetry between daughters are spatially in place in mothers before division"(line 218) for example. This should include annotation of the exact time points in minutes. The quantification can be done and presented as in their previous work, which provides the basis for this study: (Figure 2b, for example) "Allocation of gene products to daughter cells is determined by the age of the mother in single Escherichia coli cells" Chao Shi, Lin Chao, Audrey Menegaz Proenca, Andrew Qiu, Jasper Chao and Camilla U. Rang, May 2020, https://doi.org/10.1098/rspb.2020.0569.
* Quantification of variations over generations time during the time lapse is required: the change in cell-length (y-axis, the length of full-grown cell normalized to 1) vs. ribosomes number (y-axis) relative to the generation time analysis should be presented, based on the time-lapse images. The mean from ~10 independent cells should be presented, as in many similar research, for example: "Organization of Ribosomes and Nucleoids in Escherichia coli Cells during Growth and in Quiescence" Qian Chai, Bhupender Singh, Kristin Peisker, Nicole Metzendorf, Xueliang Ge, Santanu Dasgupta, Suparna Sanyal, 2014, JBC (Figure 3b).
* The distribution of ribosomes should be compared to the nucleoid distribution, as this is a major factor in RNA and translation distribution in bacterial cells (for example Gray, W. T., Govers, S. K., Xiang, Y., Parry, B. R., Campos, M., Kim, S., & Jacobs-Wagner, C. (2019). Nucleoid size scaling and intracellular organization of translation across bacteria. Cell, 177(6), 1632-1648.e20. https://doi.org/10.1016/j.cell.2019.05.017 , as reviewed in RNA localization in prokaryotes: Where, when,how, and why, Mikel Irastortza-Olaziregi, Orna Amster-Choder, 2020). The authors should add and discuss this, or elaborate on the reasons to omit this analysis.
* The results should be compared and discussed in regard to several other reports, which analyzed ribosome asymmetric distribution and inheritance in E.coli by tagging different ribosomal proteins, as well as different methodologies, including:
Organization of Ribosomes and Nucleoids in Escherichia coli Cells during Growth and in Quiescence" Qian Chai, Bhupender Singh, Kristin Peisker, Nicole Metzendorf, Xueliang Ge, Santanu Dasgupta, Suparna Sanyal, 2014, JBC
Gray, W. T., Govers, S. K., Xiang, Y., Parry, B. R., Campos, M., Kim, S., & Jacobs-Wagner, C. (2019). Nucleoid size scaling and intracellular organization of translation across bacteria. Cell, 177(6), 1632-1648.e20. https://doi.org/10.1016/j.cell.2019.05.017
Spatiotemporal Organization of the E. coli Transcriptome: Translation Independence and Engagement in Regulation Graphical Abstract Highlights d RNAs in E. coli exhibit asymmetric distribution on a transcriptome-wide scale, Shanmugapriya Kannaiah, Jonathan Livny, Orna Amster-Choder, 2019
Several of the findings reported, including asymmetric ribosome distribution and inheritance levels seem different than the ones reported here. This should be discussed in regard to the different methodologies.