In article <36ptvg$gd at mserv1.dl.ac.uk>, "RICHARD A. MURPHY 312-996-8630" <U14663 at UICVM.UIC.EDU> says:
>>When reading ODs of bacterial cultures with a spectrophotometer, what
>wavelength should be used and is it the same for all bacteria?.
In general, there is no particular WL for measuring the turbidity of a
bacterial culture.
However, 'in the old days' a commonly used WL was 578 nm since it was
one of the filters of the good old ZEISS photometers equipped with a
Hg lamp. Modern photometers have tungsten lamps in the VIS range,
with a continuous spectrum, and many people shifted to 600 nm
(probably because they thought 578 nm sounded too silly...?)
The sensitivity of the measurement is WL-dependent (decreasing with
increasing WL), so it is advisable to calibrate with dry weight or
protein per OD unit.
If you have small turbidity readings (little growth, or tiny cells),
you can use this phenomenon to significantly increase your instrument's
response by switching to, e.g., 450 nm.
If the cells are pigmented and want to rather see the increase in
turbidity than in pigmentation, you are free to choose the appropriate
WL as well.
I hope this was of help.
Andreas
Dr. Andreas Brune Phone: +49-7531-883282
Mikrobielle Oekologie Fax: +49-7531-882966
Universitaet Konstanz E-mail: Andreas.Brune at uni-konstanz.de
