Revised Estimates for the Number of Human and Bacteria Cells in the Body

<div><p>Reported values in the literature on the number of cells in the body differ by orders of magnitude and are very seldom supported by any measurements or calculations. Here, we integrate the most up-to-date information on the number of human and bacterial cells in the body. We estimate the total number of bacteria in the 70 kg "reference man" to be 3.8·10¹³. For human cells, we identify the dominant role of the hematopoietic lineage to the total count (≈90%) and revise past estimates to 3.0·10¹³ human cells. Our analysis also updates the widely-cited 10:1 ratio, showing that the number of bacteria in the body is actually of the same order as the number of human cells, and their total mass is about 0.2 kg.</p></div

B/H ratio for different population.

<p>See Table B in <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1002533#pbio.1002533.s001" target="_blank">S1 Appendix</a> for full references.</p

The distribution of the number of human cells by cell type.

<p>Representation as a Voronoi tree map where polygon area is proportional to the number of cells. Visualization performed using the online tool at <a href="http://bionic-vis.biologie.uni-greifswald.de/" target="_blank">http://bionic-vis.biologie.uni-greifswald.de/</a>.</p

Distribution of cell number and mass for different cell types in the human body (for a 70 kg adult man).

<p>The upper bar displays the number of cells, while the lower bar displays the contribution from each of the main cell types comprising the overall cellular body mass (not including extracellular mass that adds another ≈24 kg). For comparison, the contribution of bacteria is shown on the right, amounting to only 0.2 kg, which is about 0.3% of the body weight.</p

Bounds for bacteria number in different organs, derived from bacterial concentrations and volume.

<p>Bounds for bacteria number in different organs, derived from bacterial concentrations and volume.</p

Values of bacteria density in stool as reported in several past articles.

<p>Values of bacteria density in stool as reported in several past articles.</p

Back of the envelope estimate of the number of cells in an adult human body based on a characteristic volume and mass.

<p>Back of the envelope estimate of the number of cells in an adult human body based on a characteristic volume and mass.</p

Water-Transfer Slows Aging in <i>Saccharomyces cerevisiae</i>

<div><p>Transferring <i>Saccharomyces cerevisiae</i> cells to water is known to extend their lifespan. However, it is unclear whether this lifespan extension is due to slowing the aging process or merely keeping old yeast alive. Here we show that in water-transferred yeast, the toxicity of polyQ proteins is decreased and the aging biomarker 47Q aggregates at a reduced rate and to a lesser extent. These beneficial effects of water-transfer could not be reproduced by diluting the growth medium and depended on <i>de novo</i> protein synthesis and proteasomes levels. Interestingly, we found that upon water-transfer 27 proteins are downregulated, 4 proteins are upregulated and 81 proteins change their intracellular localization, hinting at an active genetic program enabling the lifespan extension. Furthermore, the aging-related deterioration of the heat shock response (HSR), the unfolded protein response (UPR) and the endoplasmic reticulum-associated protein degradation (ERAD), was largely prevented in water-transferred yeast, as the activities of these proteostatic network pathways remained nearly as robust as in young yeast. The characteristics of young yeast that are actively maintained upon water-transfer indicate that the extended lifespan is the outcome of slowing the rate of the aging process.</p></div

Without Rpn4, yeast survives poorly and is only partially rescued by water-transfer.

<p>BY4741 or Δ<i>rpn4</i> cells derived from them were grown in SC with 2% glucose. At 0.5–0.9 A₆₀₀ (logarithmic growth) cells were either transferred to water or maintained in SC with glucose. On the indicated days (A) 10-fold serial dilutions (starting with 7.5x10⁶ cells) were spotted on YPD plates, and (B) viability was monitored by PI staining as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0148650#pone.0148650.g001" target="_blank">Fig 1B</a>. (C) Growth curves were plotted from 3 biological replicates and technical triplicates within each biological replicate. Data are presented as mean ± SE.</p

Survival in water and its effect on aggregation require continuous protein synthesis.

<p>(A) W303-1b cells expressing the 25Q were grown in SC-Ura supplemented with 2% fructose (Fru). Galactose (4%) was added either immediately (Gal 0) or on the indicated following days (Gal 1–9). On the indicated days afterwards, cells were collected and lysed, and proteins were dot-blotted onto nitrocellulose. Levels of 25Q and actin were determined by quantitative immunoblotting using rabbit anti-GFP and mouse anti-actin antibodies, respectively, as descried in Materials and Methods. (B-D) W303-1b cells expressing the 47Q were logarithmically grown in SC-Ura under galactose induction. After 18 hours, cells were either kept in SC-Ura with galactose or in SC-Ura with galactose supplemented with CHX (20 μg/ml), or transferred to water or to water supplemented with CHX. On the indicated days, (B) Aggregation Index was calculated, (C) growth curves were plotted (mean ± SE of 2 biological replicates and technical triplicates within each biological replicate), and (D) CFU viability was tested by spotting on YPD plates. (E) W303-1b or BY4741 cells, logarithmically grown (0.5–0.9 A₆₀₀) in SC containing 2% glucose were either maintained in the same medium or transferred to water at logarithmic phase. Upon transfer (log) or on the following day (day 1), CHX (20 μg/ml) was added. Cells collected on the indicated days were tested for CFU viability on YPD plates. Shown is a representative experiment out of similar three.</p