# mass of bacteria

Em ekhatipoREMOVE at midway.uchicagoREMOVE.edu
Thu Apr 4 17:03:05 EST 2002

```...or, very roughly for E.coli, the culture at OD660 ~0.5/cm contains ~10^9
cells/ml or ~1g/l of dry cell mass. Given the weight of a cell is ~50% water
(very roughly indeed), the mass of a single cell is 1*2/10^9 ~ 2ng. 10 times
difference with Graham's calculation is most probably attributed to
inaccuracies of our assumptions of 1) size, 2) cell number (in particular 2
cells can be counted as 1), 3) density of the cell, 4) content of water. Of
course both dry weight and content of water per cell can be accurately
determined using standard techniques.

Emir

"Graham Shepherd" <muhero.nospam at globalnet.co.uk> wrote in message
news:a8g9gm\$b05\$1 at helle.btinternet.com...
> Smarty <smartman at comcast.net> wrote in message
> news:3cab7bd6.18969629 at news.in.comcast.giganews.com...
> > Less than 500 milligrams
> >
>
>
> You can get an approximation by calculating the volume of the organism
from
> typical dimensions (eg for E.coli assume it's a cylinder 1 micron long
with
> a diameter of 0.5 micron) and assume that the density is the same as
water.
> (It is greater, otherwise you couldn't spin them down - but it's probably
> not much greater. You could determine the density on a gradient if it's
> critical).
>
> A rough calculation indicates that the volume is about 0.2 cubic microns.
> That's 5,000,000,000 per cubic millimeter, or 5,000,000,000,000 per cubic
> cm. Assuming 1 gram per cubic cm, one bacterium weighs about 0.2 picogram.
>
> Viruses are much more variable in size than bacteria (the biggest viruses
> are bigger than the smallest bacteria). But you could do the same
> calculation for a specific virus.
>
> GS
>
>
>
>

```