mass of bacteria

Graham Shepherd muhero.nospam at globalnet.co.uk
Thu Apr 4 15:10:44 EST 2002


Colin A. B. Davidson <cabd2 at hermes.cam.ac.uk> wrote in message
news:a8hpei$s18$1 at pegasus.csx.cam.ac.uk...
>
> "Michael Witty" <mw132 at mole.bio.cam.ac.uk> wrote in message
> news:Pine.SGI.4.33.0204041523540.5154582-100000 at mole.bio.cam.ac.uk...
>
> > Colin,
> >      yes you are right.  Far from perfect.  But an experiment is married
> > to the real world.  Sitting in an office and making assumptions is how
to
> > get divorced from the real world!  Mike.
>
> I might also argue that sitting in a lab and devising experiments can be
> somewhat of a divorce from the real world. A balanced approach requires
> calculation, experimentation, and a little application! :-)
>

And intelligent use of readily-available and well established data, such as
the size and morphology of typical E. coli cells. If you don't like the
cylinder assumption you can add hemispherical ends and get closer to the
exact form (which is in any case variable).

I think the error in determining the cell numbers will limit the accuracy of
a straight weight determination, and you can most readily do a wet weight
determination by vacuum-filtering the suspension through a prewetted
preweighed membrane filter and weighing that. If you weigh the filter dry
beforehand and then dry the bacteria afterwards, you get a dry weight as
well. Half a dozen replicates should get you a reasonable figure.

I'll just leave this Cadbury's creme egg here for anyone who shows that the
experimental result is more than a factor of 2 away from the calculated
result, using an agreed set of published dimensions for the bug.

GS





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