# mass of bacteria

Nicholas Landau njl2q at virginia.edu
Mon Apr 8 23:54:08 EST 2002

```Wet weight is well over double the dry weight.  Cells are about 70% water.  In
fact, Neidhardt et al. also list the wet weight of your average cell, at
9.5E-13 g.  Same page, same book.

--Nick

Graham Shepherd wrote:

> Nicholas Landau <njl2q at virginia.edu> wrote in message
> news:3CB11E37.D05743F9 at virginia.edu...
> >
> > For what it is worth, Neidhardt et al. do list a figure for the dry weight
> of a
> > single E. coli cell in their microbial physiology text."  The figure they
> list
> > is 2.9 E-13 g.  The do not include any citations for this figure
> specifically,
> > but they do state that it is "an average of many measurements..."
> Neidhardt,
> > F.C., J. L. Ingraham, and M. Schaecher.  1990.  Physiology of the
> Bacterial
> > Cell.  Sunderland, Mass: Sinauer Associates.
>
> So the dry weight is 0.29 picograms - if wet weight is about double the dry
> weight that makes it 0.6 picograms. My original very crude estimate was 0.2
> picograms. Do Neidhardt et al also publish average dimensions and density?
> If so, we can recalculate using a formula for a cylinder with hemispherical
> ends and see how close a derived weight is to a measured value.
>
> GS
>
> > Would you like the mailing address for that egg?
> >
> > Incidentally, who said that the largest viruses are larger than the
> smallest
> > bacteria?  I have to admit, I know little about viruses, but I can hardly
> > believe that statement is true.  What virus is as large as a bacterium?
> >
> > Em wrote:
> >
> > > ...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
> > > > >
> > > >
> > > > An unusually unhelpful response.
> > > >
> > > > 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
> > > >
> > > >
> > > >
> > > >
> >

```