Gerard Tromp tromp at sanger.med.wayne.edu
Tue Aug 18 20:49:31 EST 1998

ProteusX wrote:
> skyamsen wrote in message <6pq3s8$e43$1 at mawar.singnet.com.sg>...
> >what wavelength should one be using to detect marine bacteria?  I know
> 610nm
> >and 660nm were suggested.  why and is it correct?
> 660 nm would detect chlorophyll a
> and 610 nm would detect phycocyanin
> Both of these wavelengths would detect organisms capable of photosynthesis
> e.g.. algae, phytoplankton and seaweed.
> Check other frequencies I can not remember any off-hand.
> The only sure way is to sample, filter, stain and count.
> For the stain I would suggest Acridine orange (stains DNA green)
> Best wishes
> ProteusX
> --

	My recollection is that wavelengths in the range of 550 to 660 are used
to measure "scattering" or turbidity. They are appropriate for
microorganisms due to the refraction of light of those wavelengths
around the objects of about 1 um in size. One problem with this
technique is that it gives a representation proportional to the number
of "objects" in solution, i.e. it does not differenitate between live
and dead bacteria. To discriminate live from dead organisms, titration,
growth and colony counting is required.

	As pointed out, though, absorption can be a confounder. If the objects
both scatter and absorb, one has a problem.

Gerard Tromp, Ph.D.
CMMG, Wayne State University    vox:	313-577-8773
3116, Scott Hall		fax: 	313-577-5218
540 E Canfield Ave		e-mail: tromp at sanger.med.wayne.edu
Detroit, MI 48201                       gtromp at cmb.biosci.wayne.edu

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