O.D. 600 nm readings to bacterial concentrations

Lesley Robertson l.a.robertson at stm.tudelft.nl
Thu Oct 5 05:06:05 EST 1995

dbk at aber.ac.uk (Douglas B. Kell) wrote:
>In article <44rnn6$89o at news.internetmci.com> "Gregory P. Harhay" <gpharhay at internetmci.com> writes:
>>I need to convert my O.D. 600 nm "absorption" readings of pure
>>cultures of Pseudomonas fluorescens (ATCC 13525) and 
>>Brochothrix thermosphacta  (ATCC 11509) suspended in buffer
>>to an estimate of their concentration in the buffer. Are there
>>any good references out there? ATCC is no help
>>Greg Harhay
>Just to be (not in fact) pedantic, please drop the "absorption" or
>even absorbance. OD is NOT absorbance (but scattering). Rule of
>thumb for bugs says (in the Beer-Lambert range, typically up to OD
>0.6) that 1 OD = 0.5 mg dw/ml. Every bug is different, and
>it depends on where the cuvette is in the spec and the optics 
>thereof - you have to make your own calibration curve. The ref I
>usually cite is Mallette, M.F. (1969) Evaluation of growth by 
>physical and chemical means. in Methods in Microbiology (ed. 
>JR Norris & DW Ribbons) Vol 1, 521-566. Academic Press, 

Hello Douglas!
  you forgot to mention that it also depends on the growth conditins - if 
the bacteria decide to make storage products, that increases their size 
without increasing their numbers/amount of active biomass.
Lesley Robertson

Dr. Lesley A. Robertson
Kluyver Laboratory for Biotechnology
Delft University of Technology, the Netherlands
L.A.Robertson at stm.tudelft.nl

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