bacterial cell densities

Romantschuk Martin L romantsc at biocenter.helsinki.fi
Tue Mar 2 03:22:12 EST 1999


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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