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. Author manuscript; available in PMC: 2022 Sep 22.
Published in final edited form as: Cell Syst. 2021 Jul 1;12(9):924–944.e2. doi: 10.1016/j.cels.2021.06.002

Figure 4. Influence of cell size and surface area to volume ratio on ATP production and inner membrane composition.

Figure 4.

(A) Scaling of ATP demand and maximum ATP production through respiration as a function of surface area to volume ratio. Cell volumes of 0.5 fL to 50 fL were considered, with the dashed ( - -) line corresponding to a sphere and the dash-dot line (−.) reflecting a rod-shaped bacterium like E. coli with a typical aspect ratio (length/width) of 4 (Shi et al., 2018). The ATP demand is calculated as 106 ATP/(μm3 s), while the maximum ATP production rate is taken to be 3 ATP / (nm2•s) (Szenk et al., 2017), with calculations of E. coli volume and surface area detailed in supplemental information section “estimation of cell size and surface area.” In this calculation, 50% of the bacterial inner membrane is assumed to be protein, with the remainder lipid.

(B) Total protein mass per μm2 calculated for proteins with inner membrane annotation (GO term: 0005886).

(C) Relative protein abundances are grouped by their COG annotations (“metabolic,” “cellular processes and signaling,” “information storage and processing,” and “poorly characterized or not annotated”) for the data from Schmidt et al. (2016). Metabolic proteins are further separated into respiration (F1-F0 ATP synthase, NADH dehydrogenase I, succinate:quinone oxidoreductase, cytochrome bo3 ubiquinol oxidase, cytochrome bd-I ubiquinol oxidase) and carbohydrate transport (GO term: GO:0008643). Note that the elongation factor EF-Tu can also associate with the inner membrane but was excluded in this analysis due to its high relative abundance (roughly identical to the summed protein shown in B).

(D) Relative cytosolic protein abundances (GO term: 0005886), grouped by their COG annotations, are plotted as a function of growth rate.

(E) The relative cytosolic protein abundances (GO term: 0005886) associated with the “information storage and processing” and “metabolic” COG categories are plotted against each other and highlight the larger mass fraction devoted to “information storage and processing” at faster growth rates.