Dear Mark
You can probably run an isopycnic sucrose (or CsCl) density gradient,
and you do not need standards. If it is in equilibrium (which is has
to be to be usable) you simply sample the band (visualized by
lightscattering) and determine the density of it (grams/ml of e.g.
100 ul). You can also collect the whole gradient into fractions and
weigh each fraction to get a "curve", and then you measure (by
dinstance from the top or something) in which fraction the bacterium
bands.
However, in the high osmolarity of the gradient the liquid will be
sucked our of the cell and make their density higher than in water or
normal media.
For phages and viruses lots of such determinations have been done.
Martin Romantschuk
Viikki Biocenter
Dept Biosciences
U of Helsinki
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